Publications

The scanning superconducting quantum interference device (SQUID) fabricated on the tip of a sharp quartz pipette (SQUID-on-tip) has emerged as a versatile tool for the nanoscale imaging of magnetic, thermal, and transport properties of microscopic devices of quantum materials. We present the design and performance of a scanning SQUID-on-tip microscope in a top-loading probe of a cryogen-free dilution refrigerator. The microscope is enclosed in a custom-made vacuum-tight cell mounted at the bottom of the probe and is suspended by springs to suppress vibrations caused by the pulse tube cryocooler. Two capillaries allow for the in situ control of helium exchange gas pressure in the cell that is required for thermal imaging. A nanoscale heater is used to create local temperature gradients in the sample, which enables quantitative characterization of relative vibrations between the tip and the sample. The spectrum of the vibrations shows distinct resonant peaks with a maximal power density of about 27 nm/Hz1/2 in the in-plane direction. The performance of the SQUID-on-tip microscope is demonstrated by magnetic imaging of the MnBi2Te4 magnetic topological insulator, magnetization and current distribution imaging in a SrRuO3 ferromagnetic oxide thin film, and thermal imaging of dissipation in graphene.

A new method for cooling beams of any ion is introduced. The method is autoresonance acceleration of ions inside an Electrostatic Ion Beam Trap. Intrabunch collisions of trapped (molecular) ions transfer energy from the "cold" part of the population of the ion distribution to the "hot" part, which, in turn, evaporates from the bunch. As a result, bunches of ions were cooled from about 45 K to well below 1 K.

A new hybrid electrostatic ion beam trap (HEIBT) is designed and simulated for low-energy ion-ion, ion-neutral merged beam collision studies as well as ion-laser interaction experiments. The HEIBT is made possible by the design of dichroic electrostatic mirrors that reflect or transmit ion beams of different charge and energy. The experimental setup allows fragment imaging detection of the investigated reaction products ejected outside the trap.

We present the development of the End-to-End simulator for the SOXS instrument at the ESO-NTT 3.5-m telescope. SOXS will be a spectroscopic facility, made by two arms high efficiency spectrographs, able to cover the spectral range 350-2000 nm with resolving power R≈4500. The E2E model allows to simulate the propagation of photons starting from the scientific target of interest up to the detectors. The outputs of the simulator are synthetic frames, which will be mainly exploited for optimizing the pipeline development and possibly assisting for proper alignment and integration phases in laboratory and at the telescope. In this paper, we will detail the architecture of the simulator and the computational model, which are strongly characterized by modularity and flexibility. Synthetic spectral formats, related to different seeing and observing conditions, and calibration frames to be ingested by the pipeline are also presented.

Scanning nanoscale superconducting quantum interference devices (SQUIDs) are gaining interest as highly sensitive microscopic magnetic and thermal characterization tools of quantum and topological states of matter and devices. We introduce a technique of collimated differential-pressure magnetron sputtering for versatile self-aligned fabrication of SQUID-on-tip (SOT) nanodevices, which cannot be produced by conventional sputtering methods due to their diffusive, rather than the required directional point source, deposition. The technique provides access to a broad range of superconducting materials and alloys beyond the elemental superconductors employed in the existing thermal deposition methods, opening the route to greatly enhanced SOT characteristics and functionalities. Utilizing this method, we have developed molybdenum-rhenium (Mo66Re34) SOT devices with sub-50-nm diameter, magnetic flux sensitivity of 1.2 μφ0/Hz1/2 up to 3 T at 4.2 K, and thermal sensitivity better than 4 μK/Hz1/2 up to 5 T-about five times higher than any previous report-paving the way to nanoscale imaging of magnetic and spintronic phenomena and of dissipation mechanisms in previously inaccessible quantum states of matter.

A novel experiment has been commissioned at the Weizmann Institute of Science for the study of weak interactions via a high-precision measurement of the beta-neutrino angular correlation in the radioactive decay of short-lived(6)He. The facility consists of a 14 MeV d + t neutron generator to produce atomic(6)He, followed by ionization and bunching in an electron beam ion source, and injection into an electrostatic ion beam trap. This ion trap has been designed for efficient detection of the decay products from trapped light ions. The storage time in the trap for different stable ions was found to be in the range of 0.6 to 1.2 s at the chamber pressure of similar to 7 x 10(-10) mbar. We present the initial test results of the facility, and also demonstrate an important upgrade of an existing method (Stora et al., 2012) for production of light radioactive atoms, viz.He-6, for the precision measurement. The production rate of(6)He atoms in the present setup has been estimated to be similar to 1.45 x 10(-4) atoms per neutron, and the system efficiency was found to be 4.0 +/- 0.6%. An improvement to this setup is also presented for the enhanced production and diffusion of radioactive atoms for future use.

Isomerization and carbon chemistry in the gas phase are key processes in many scientific studies. Here we report on the isomerization process from linear $${{\rm C}}-{10}^ -$$ C 10 - to its monocyclic isomer. $${{\rm C}}-{10}^ -$$ C 10 - ions were trapped in an electrostatic ion beam trap and then excited with a laser pulse of precise energy. The neutral products formed upon photoexcitation were measured as a function of time after the laser pulse. It was found using a statistical model that, although the system is excited above its isomerization barrier energy, the actual isomerization from linear to monocyclic conformation takes place on a very long time scale of up to hundreds of microseconds. This finding may indicate a general phenomenon that can affect the interstellar medium chemistry of large molecule formation as well as other gas phase processes.

We present an experimental plan to study the weak interaction by measuring the electron-neutrino angular correlation from radioactive β-emitter atoms, 6He being the first case. Radioactive atoms, produced by a neutroninduced reaction, will diffuse to an electron beam ion source that ionizes, bunches and then injects them into an electrostatic ion beam trap where the angular correlation will be measured. We have tested the trap with stable ions and found the storage time to be 0.6 to 1.2 s for different ions. We have also performed the production experiment for ⁶He with a production rate of - 10⁵ atoms/s. We present the current status of this project and future plans.

SOXS (Son Of X-Shooter) is a new spectrograph for the ESO NTT telescope, currently in the final design phase. The main instrument goal is to allow the characterization of transient sources based on alerts. It will cover from near-infrared to visible bands with a spectral resolution of R 1/4 4500 using two separate, wavelength-optimized spectrographs. A visible camera, primarily intended for target acquisition and secondary guiding, will also provide a scientific "light" imaging mode. In this paper we present the current status of the design of the SOXS instrument control software, which is in charge of controlling all instrument functions and detectors, coordinating the execution of exposures, and implementing all observation, calibration and maintenance procedures. Given the extensive experience of the SOXS consortium in the development of instruments for the VLT, we decided to base the design of the Control System on the same standards, both for hardware and software control. We illustrate the control network, the instrument functions and detectors to be controlled, the overall design of SOXS Instrument Software (INS) and its main components. Then, we provide details about the control software for the most SOXS-specific features: Control of the COTS-based imaging camera, the flexures compensation system and secondary guiding.

SOXS (Son Of X-Shooter) is a unique spectroscopic facility that will operate at the ESO New Technology Telescope (NTT) in La Silla from 2021 onward. The spectrograph will be able to cover simultaneously the UV-VIS and NIR bands exploiting two different arms and a Common Path feeding system. We present the design of the SOXS instrument control electronics. The electronics controls all the movements, alarms, cabinet temperatures, and electric interlocks of the instrument. We describe the main design concept. We decided to follow the ESO electronic design guidelines to minimize project time and risks and to simplify system maintenance. The design envisages Commercial Off-The-Shelf (COTS) industrial components (e.g. Beckhoff PLC and EtherCAT fieldbus modules) to obtain a modular design and to increase the overall reliability and maintainability. Preassembled industrial motorized stages are adopted allowing for high precision assembly standards and a high reliability. The electronics is kept off-board whenever possible to reduce thermal issues and instrument weight and to increase the accessibility for maintenance purpose. The instrument project went through the Preliminary Design Review in 2017 and is currently in Final Design Phase (with FDR in July 2018). This paper outlines the status of the work and is part of a series of contributions describing the SOXS design and properties after the instrument Preliminary Design Review.

SOXS (Son Of X-Shooter) will be a spectrograph for the ESO NTT telescope capable to cover the optical and NIR bands, based on the heritage of the X-Shooter at the ESO-VLT. SOXS will be built and run by an international consortium, carrying out rapid and longer term Target of Opportunity requests on a variety of astronomical objects. SOXS will observe all kind of transient and variable sources from different surveys. These will be a mixture of fast alerts (e.g. gamma-ray bursts, gravitational waves, neutrino events), mid-term alerts (e.g. supernovae, X-ray transients), fixed time events (e.g. close-by passage of minor bodies). While the focus is on transients and variables, still there is a wide range of other astrophysical targets and science topics that will benefit from SOXS. The design foresees a spectrograph with a Resolution-Slit product ∼ 4500, capable of simultaneously observing over the entire band the complete spectral range from the U- to the H-band. The limiting magnitude of R∼20 (1 hr at S/N∼10) is suited to study transients identified from on-going imaging surveys. Light imaging capabilities in the optical band (grizy) are also envisaged to allow for multi-band photometry of the faintest transients. This paper outlines the status of the project, now in Final Design Phase.

SOXS (Son of X-Shooter) will be the new medium resolution (R∼4500 for a 1 arcsec slit), high-efficiency, wide band spectrograph for the ESO-NTT telescope on La Silla. It will be able to cover simultaneously optical and NIR bands (350-2000nm) using two different arms and a pre-slit Common Path feeding system. SOXS will provide an unique facility to follow up any kind of transient event with the best possible response time in addition to high efficiency and availability. Furthermore, a Calibration Unit and an Acquisition Camera System with all the necessary relay optics will be connected to the Common Path sub-system. The Acquisition Camera, working in optical regime, will be primarily focused on target acquisition and secondary guiding, but will also provide an imaging mode for scientific photometry. In this work we give an overview of the Acquisition Camera System for SOXS with all the different functionalities. The optical and mechanical design of the system are also presented together with the preliminary performances in terms of optical quality, throughput, magnitude limits and photometric properties.

Son Of X-Shooter (SOXS) is the new instrument for the ESO 3.5 m New Technology Telescope (NTT) in La Silla site (Chile) devised for the spectroscopic follow-up of transient sources. SOXS is composed by two medium resolution spectrographs able to cover the 350-2000 nm interval. An Acquisition Camera will provide a light imaging capability in the visible band. We present the procedure foreseen for the Assembly, Integration and Test activities (AIT) of SOXS that will be carried out at sub-systems level at various consortium partner premises and at system level both in Europe and Chile.

Son of X-Shooter (SOXS) will be a high-efficiency spectrograph with a mean Resolution-Slit product of 4500 (goal 5000) over the entire band capable of simultaneously observing the complete spectral range 350-2000 nm. It consists of three scientific arms (the UV-VIS Spectrograph, the NIR Spectrograph and the Acquisition Camera) connected by the Common Path system to the NTT and the Calibration Unit. The Common Path is the backbone of the instrument and the interface to the NTT Nasmyth focus flange. The light coming from the focus of the telescope is split by the common path optics into the two different optical paths in order to feed the two spectrographs and the acquisition camera. The instrument project went through the Preliminary Design Review in 2017 and is currently in Final Design Phase (with FDR in July 2018). This paper outlines the status of the Common Path system and is accompanied by a series of contributions describing the SOXS design and properties after the instrument Preliminary Design Review.

SOXS (Son of X-shooter) is a wide band, medium resolution spectrograph for the ESO NTT with a first light expected in early 2021. The instrument will be composed by five semi-independent subsystems: a pre-slit Common Path (CP), an Acquisition Camera (AC), a Calibration Unit (CU), the NIR spectrograph, and the UV-VIS spectrograph. In this paper, we present the mechanical design of the subsystems, the kinematic mounts developed to simplify the final integration procedure and the maintenance. The concept of the CP and NIR optomechanical mounts developed for a simple pre- alignment procedure and for the thermal compensation of reflective and refractive elements will be shown.

We present the NIR spectrograph of the Son Of XShooter (SOXS) instrument for the ESO-NTT telescope at La Silla (Chile). SOXS is a R∼4,500 mean resolution spectrograph, with a simultaneously coverage from about 0.35 to 2.00 μm. It will be mounted at the Nasmyth focus of the NTT. The two UV-VIS-NIR wavelength ranges will be covered by two separated arms. The NIR spectrograph is a fully criogenic echelle-dispersed spectrograph, working in the range 0.80- 2.00 μm, equipped with an Hawaii H2RG IR array from Teledyne, working at 40 K. The spectrograph will be cooled down to about 150 K, to lower the thermal background, and equipped with a thermal filter to block any thermal radiation above 2.0 μm. In this poster we will show the main characteristics of the instrument along with the expected performances at the telescope.

SOXS will be a unique spectroscopic facility for the ESO NTT telescope able to cover the optical and NIR bands thanks to two different arms: the UV-VIS (350-850 nm), and the NIR (800-1800 nm). In this article, we describe the design of the visible camera cryostat and the architecture of the acquisition system. The UV-VIS detector system is based on a e2v CCD 44-82, a custom detector head coupled with the ESO continuous flow cryostats (CFC) cooling system and the NGC CCD controller developed by ESO. This paper outlines the status of the system and describes the design of the different parts that made up the UV-VIS arm and is accompanied by a series of contributions describing the SOXS design solutions (Ref. 1-12).

The Son Of X-Shooter (SOXS)1 is a medium resolution spectrograph (R ∼ 4500) proposed for the ESO 3.6m NTT. We present the optical design of the UV-VIS arm of SOXS which employs high efficiency ion-etched gratings used in first order (m = 1) as the main dispersers. The spectral band is split into four channels which are directed to individual gratings, and imaged simultaneously by a single three-element catadioptric camera. The expected throughput of our design is > 60% including contingency. The SOXS collaboration expects first light in early 2021. This paper is one of several papers presented in these proceedings_2-10 describing the full SOXS instrument.

An overview of the optical design for the SOXS spectrograph is presented. SOXS (Son Of X-Shooter) is the new wideband, medium resolution (R>4500) spectrograph for the ESO 3.58m NTT telescope expected to start observations in 2021 at La Silla. The spectroscopic capabilities of SOXS are assured by two different arms. The UV-VIS (350-850 nm) arm is based on a novel concept that adopts the use of 4 ion-etched high efficiency transmission gratings. The NIR (800- 2000 nm) arm adopts the 4C' design (Collimator Correction of Camera Chromatism) successfully applied in X-Shooter. Other optical sub-systems are the imaging Acquisition Camera, the Calibration Unit and a pre-slit Common Path. We describe the optical design of the five sub-systems and report their performance in terms of spectral format, throughput and optical quality. This work is part of a series of contributions^1-9 describing the SOXS design and properties as it is about to face the Final Design Review.

The bubble-assisted Liquid Hole-Multiplier (LHM) is a recently-introduced detection concept for noble liquid time projection chambers. In this "local dual-phase" detection element, a gas bubble is supported underneath a perforated electrode (e.g., Thick Gas Electron Multiplier - THGEM, or Gas Electron Multiplier - GEM). Electrons drifting through the holes induce large electroluminescence signals as they pass into the bubble. In this work we report on recent results of THGEM and GEM electrodes coated with cesium iodide and immersed in liquid xenon, allowing - for the first time - the detection of primary VUV scintillation photons in addition to ionization electrons.

A Velocity Map Imaging (VMI) spectrometer has been designed and integrated with an electrostatic ion beam trap to study delayed electron emission from trapped polyatomic anions upon photodetachment. The VMI spectrometer is small in size and can record a wide range of photoelectron energies, with variable magnification. Delayed electron emission can be recorded in our experimental setup for any time duration after the photoexcitation of the polyatomic anions. Experiments were carried out with trapped O- and C-5(-) ions to demonstrate the capability of the spectrometer. Delayed electron emissions from C-5(-) as well as prompt photoelectrons from O- were detected by the VMI spectrometer upon photoexcitation. The design and performance of the spectrometer are presented in detail.

Among the advantages of an electrostatic ion beam trap (EIBT), which is based on purely electrostatic fields, are mass-unlimited trapping and ease of operation. We have developed a new system that couples an electrospray ion source to an EIBT. Between the source and EIBT there is a Paul trap in which the ions are accumulated before being extracted and accelerated. After the ion bunch has entered the EIBT, the ions are trapped by rapidly raising the voltages on the entrance mirror. The oscillations of the bunch are detected by amplifying the charge induced on a pickup ring in the center of the trap, the ion mass being directly proportional to the square of the oscillation period. The trapping of biomolecules in the RF-bunching mode of the EIBT is used for measurement of mass spectra and collision cross sections. Coalescence of bunches of ions of nearby mass in the self-bunching mode is also demonstrated.

Autoresonance (AR) cooling of a bunch of ions oscillating inside an electrostatic ion beam trap is demonstrated for the first time. The relatively wide initial longitudinal velocity distribution is reduced by at least an order of magnitude using AR acceleration and ramping forces. The hot ions escaping the bunch are not lost from the system but continue to oscillate in the trap outside of the bunch and may be further cooled by successive AR processes. Ion-ion collisions inside the bunch close to the turning points in the trap's mirrors contribute to the thermalization of the ions. This cooling method can be applied to any mass and any charge.

Radiative electron attachment (REA) plays an important role in forming molecular anions in various astrophysical environments. In this work, we determined the rate coefficient for the formation of C-6(-) by REA based on a detailed balance approach. C-6(-) ions are stored in an electrostatic ion beam trap and are photoexcited above their adiabatic detachment energy (4.18 eV). Due to fast internal conversion and intramolecular vibrational redistribution, photoexcitation leads to the formation of temporary negative ions (TNIs), the same as those one formed by the electron attachment. Absolute vibrational autodetachment and recurrent (or Poincare) fluorescence (RF) rate coefficients have already been reported [V. Chandrasekaran et al., J. Phys. Chem. Lett. 5, 4078 (2014)]. Knowing the branching ratios of the various competing rate coefficients is decisive to the understanding of the formation probability of anions via REA. The radiative stabilization rate of C-6(-), shown to be dominated by RF, was determined to be 5 x 10(4) s(-1) at the electron detachment energy, i.e., at least a factor of 100 faster than the stabilization by infrared transitions. The RF is found to very effectively stabilize the TNI formed by electron attachment. Using detailed balance to link the measured delayed detachment rate to the rate of electron attachment, we estimate the REA rate leading to the formation of C-6(-) to be 3 x 10(-7) cm(3) s(-1) at 300 K in agreement with theory (1.7 x 10(-7) cm(3) s(-1) [R. Terzieva and E. Herbst, Int. J. Mass Spectrom. 201, 135 (2000)]). Such a high rate for REA to C-6 indicates that REA may play a prominent role in the formation of anions in the interstellar medium.

Resistive anode multichannel plate detectors are extensively used for imaging photons, electrons and ions. We present a method to acquire position information from such detector systems by considering simple parameters of the signals produced from the resistive anode encoder. Our technique is easy to implement and computes position in real time during experiments. Position information can be obtained using our method without the need for dedicated position analyser units.

An electrostatic cryogenic storage ring, CSR, for beams of anions and cations with up to 300 keV kinetic energy per unit charge has been designed, constructed, and put into operation. With a circumference of 35 m, the ion-beam vacuum chambers and all beam optics are in a cryostat and cooled by a closed-cycle liquid helium system. At temperatures as low as (5.5 +/- 1) K inside the ring, storage time constants of several minutes up to almost an hour were observed for atomic and molecular, anion and cation beams at an energy of 60 keV. The ion-beam intensity, energy-dependent closed-orbit shifts (dispersion), and the focusing properties of the machine were studied by a system of capacitive pickups. The Schottky-noise spectrum of the stored ions revealed a broadening of the momentum distribution on a time scale of 1000 s. Photodetachment of stored anions was used in the beam lifetime measurements. The detachment rate by anion collisions with residual-gas molecules was found to be extremely low. A residual-gas density below 140 cm(-3) is derived, equivalent to a room-temperature pressure below 10(-14) mbar. Fast atomic, molecular, and cluster ion beams stored for long periods of time in a cryogenic environment will allow experiments on collision-and radiation-induced fragmentation processes of ions in known internal quantum states with merged and crossed photon and particle beams.

Ions in an ion bunch trapped inside an Electrostatic Ion Beam Trap (EIBT) exhibit collective oscillations within the bunch under the influence of an external driving force. These internal oscillations have been measured explicitly using a new method with a particle detector outside the EIBT. In this approach, the evolving ion bunch is monitored along the entire trap length, in contrast to the localized single point measurements that are often carried out in other techniques. In the present study, quadrupole oscillations have been measured for the first time in an EIBT along with the dipole oscillations that were measured previously. The frequency of the quadrupole oscillation is found to be about twice the dipole oscillation frequency. This is in agreement with the prediction of a theoretical model.

Atomically sharp oxide heterostructures exhibit a range of novel physical phenomena that are absent in the parent compounds. A prominent example is the appearance of highly conducting and superconducting states at the interface between LaAlO 3 and SrTiO 3. Here we report an emergent phenomenon at the LaMnO₃/SrTiO₃ interface where an antiferromagnetic Mott insulator abruptly transforms into a nanoscale inhomogeneous magnetic state. Upon increasing the thickness of LaMnO₃, our scanning nanoSQUID-on-tip microscopy shows spontaneous formation of isolated magnetic nanoislands, which display thermally activated moment reversals in response to an in-plane magnetic field. The observed superparamagnetic state manifests the emergence of thermodynamic electronic phase separation in which metallic ferromagnetic islands nucleate in an insulating antiferromagnetic matrix. We derive a model that captures the sharp onset and the thickness dependence of the magnetization. Our model suggests that a nearby superparamagnetic-ferromagnetic transition can be gate tuned, holding potential for applications in magnetic storage and spintronics.

Absolute photoabsorption cross sections of negatively charged tetra-atomic aluminum clusters have been measured for photon energies between 1.8 and 2.7 eV. The experiment used the depletion technique in combination with an electrostatic ion-beam trap, in which Al 4- ions produced in a sputter ion source were stored for 90 ms before being subjected to a short laser pulse. Moreover, the competition between one-atom fragmentation and electron emission of the laser-excited Al 4- has been measured. These measurements show that fragmentation dominates electron emission at all photon energies below the electron attachment energy of ~2.2 eV, even though the fragmentation energy is expected to be 10%-20% higher than the electron attachment energy. These findings, when taken together with the delayed-electron and fragmentation yields observed in a previous measurement [O. Aviv, Phys. Rev. A83, 023201 (2011)PLRAAN1050-294710.1103/PhysRevA.83.023201], can be well explained within the statistical phase-space theory for unimolecular decays assuming the Al 4- ions to be rotationally hot. The analysis permits the determination of the adiabatic electron detachment energy of Al 4- to be E ad = (2.18 +or- 0.02) eV and the one-atom fragmentation energy to be D 0 = (2.34 +or- 0.05) eV. Moreover, two direct s-wave ionization channels are observed with threshold energies of (2.18 +or- 0.02) eV and (2.45 +or- 0.02) eV.

We discuss recent advances in the development of cryogenic gaseous photomultipliers (GPM), for possible use in dark matter and other rare-event searches using noble-liquid targets. We present results from a 10 cm diameter GPM coupled to a dual-phase liquid xenon (LXe) TPC, demonstrating - for the first time - the feasibility of recording both primary (''S1'') and secondary (''S2'') scintillation signals. The detector comprised a triple Thick Gas Electron Multiplier (THGEM) structure with cesium iodide photocathode on the first element; it was shown to operate stably at 180 K with gains above 10⁵, providing high single-photon detection efficiency even in the presence of large α particle-induced S2 signals comprising thousands of photoelectrons. S1 scintillation signals were recorded with a time resolution of 1.2 ns (RMS). The energy resolution (σ/E) for S2 electroluminescence of 5.5 MeV α particles was ∼ 9%, which is comparable to that obtained in the XENON100 TPC with PMTs. The results are discussed within the context of potential GPM deployment in future multi-ton noble-liquid detectors.

Bubble formation in liquid xenon underneath a Thick Gaseous Electron Multiplier (THGEM) electrode immersed in liquid xenon was observed with a CCD camera. With voltage across the THGEM, the appearance of bubbles was correlated with that of electroluminescence signals induced by ionization electrons from alpha-particle tracks. This confirms recent indirect evidence that the observed photons are due to electroluminescence within a xenon vapor layer trapped under the electrode. The bubbles seem to emerge spontaneously due to heat flow from 300 K into the liquid, or in a controlled manner by locally boiling the liquid with resistive wires. Controlled bubble formation resulted in energy resolution of σ/E 7.5% for ∼ 6000 ionization electrons. The phenomenon could pave ways towards the conception of large-volume 'local dual-phase' noble-liquid TPCs.

We have designed a velocity map imaging (VMI) setup and integrated it with an Electrostatic Ion Beam Trap (EIBT) to study photon induced prompt and delayed electron emission from trapped cluster anions. The operational details are discussed here. The performance of the VMI is also reported for photoionization of trapped O- ions.

The dynamics of quantized magnetic vortices and their pinning by materials defects determine electromagnetic properties of superconductors, particularly their ability to carry non-dissipative currents. Despite recent advances in the understanding of the complex physics of vortex matter, the behavior of vortices driven by current through a multi-scale potential of the actual materials defects is still not well understood, mostly due to the scarcity of appropriate experimental tools capable of tracing vortex trajectories on nanometer scales. Using a novel scanning superconducting quantum interference microscope we report here an investigation of controlled dynamics of vortices in lead films with sub-Angstrom spatial resolution and unprecedented sensitivity. We measured, for the first time, the fundamental dependence of the elementary pinning force of multiple defects on the vortex displacement, revealing a far more complex behavior than has previously been recognized, including striking spring softening and broken-spring depinning, as well as spontaneous hysteretic switching between cellular vortex trajectories. Our results indicate the importance of thermal fluctuations even at 4.2K and of the vital role of ripples in the pinning potential, giving new insights into the mechanisms of magnetic relaxation and electromagnetic response of superconductors.

In this work we discuss the mechanism behind the large electroluminescence signals observed at relatively low electric fields in the holes of a Thick Gas Electron Multiplier (THGEM) electrode immersed in liquid xenon. We present strong evidence that the scintillation light is generated in xenon bubbles trapped below the THGEM holes. The process is shown to be remarkably stable over months of operation, providing - under specific thermodynamic conditions - energy resolution similar to that of present dual-phase liquid xenon experiments. The observed mechanism may serve as the basis for the development of Liquid Hole Multipliers (LHMs), capable of producing local charge-induced electroluminescence signals in large-volume single-phase noble-liquid detectors for dark matter and neutrino physics experiments.

Dual-phase noble-liquid TPCs are presently the most sensitive instruments for direct dark matter detection. Scaling up existing ton-scale designs to the multi-ton regime may prove to be technologically challenging. This includes both large-area coverage with affordable high-QE UV-photon detectors, and maintaining high precision in measuring the charge and light signals of rare events with keV-scale energy depositions. We present our recent advances in two complementary approaches to these problems: large-area cryogenic gaseous photomultipliers (GPM) for UV-photon detection, and liquid-hole multipliers (LHM) that provide electroluminescence light in response to ionization electrons and primary scintillation photons, using perforated electrodes immersed within the noble liquid. Results from a 10 cm diameter GPM coupled to a dual-phase liquid- xenon TPC demonstrate the feasibility of recording - for the first time - both primary (ldquoS1rdquo) and secondary (ldquoS2rdquo) scintillation signals, over a very broad dynamic range. The detector, comprising a triple-THGEM structure with CsI on the first element, has been operating stably at 180 K with gains larger than 10 5; it provided high single-photon detection efficiency - in the presence of massive alpha-particle induced S2 signals; S1 scintillation signals were recorded with time resolutions of 1.2 ns (RMS). Results with the LHM operated in liquid xenon yielded large photon gains, with a pulse-height resolution of 11% (RMS) for alpha-particle induced S2 signals. The detector response was stable over several months. The response of the S2 signals to rapid changes in pressure lead to the conclusion that the underlying mechanism for S2 light is electroluminescence in xenon bubbles trapped below the immersed THGEM electrode. Both studies have the potential of paving the way towards new designs of dual- and single-phase noble-liquid TPCs that could simplify the conception of future multi-ton detectors of dark matter and other rare events.

Absolute rate coefficients were determined for the recurrent fluorescence (RF) process in C₆^- anions at excitation energies above the adiabatic electron attachment energy. The RF process is an important ingredient in understanding the formation and stabilization of anions in the interstellar medium.

We determined absolute rate coefficients for the recurrent fluorescence (RF) process in C₆^- anions at excitation energies above the adiabatic electron attachment energy of 4.18 eV. The experiment was performed by extracting C6^- ions from a sputter ion source and storing them in a bent electrostatic ion beam trap. After 1 s of storage, during which the anions cooled down to temperatures close to room temperature, they were excited by a short laser pulse and the neutralization rate due to vibrational autodetachment (VAD) was measured as a function of time at several wavelengths. Due to the different energy dependence of the two competing decays via the RF and the VAD process, their contributions to the measured total decay rate coefficients could be disentangled. For excitation energies 4.6 eV, the decay is found to be dominated by the RF process with decay rate coefficients on the order of 5 × 10⁴ s^-1. The result clearly demonstrates the presence of the RF process in C6 and illustrates the importance of this process in the production and cooling of isolated molecules of astrophysical interest.

A technique for mass-selective lifetime measurements of keV ions in a linear electrostatic ion beam trap is presented. The technique is based on bunching the ions using a weak RF potential and non-destructive ion detection by a pick-up electrode. This method has no mass-limitation, possesses the advantage of inherent mass-selectivity, and offers a possibility of measuring simultaneously the lifetimes of different ion species with no need for prior mass-selection.

We present the first steps towards the realization of a novel experimental scheme to measure β-ν correlations in the β decay of ⁶He, for the purpose of Fundamental Interaction studies. Our method is based on a novel use of an ion trapping device, the Electrostatic Ion Beam Trap (EIBT) coupled to a d+t neutron generator. The EIBT which has not been previously considered for Fundamental Interaction studies, exhibits potentially very significant advantages over other state of the art experimental schemes aimed at precision measurements of the β-ν angular correlation coefficient.

We measured the effects of periodic surface holes, created using a focused ion beam, on the phase diagram of the vortex matter in high- Tc Bi2 Sr2 CaCu2 O8+δ crystals. Differential magneto-optical measurements show that the irreversibility line is shifted to higher fields and temperatures with respect to the pristine melting line. The irreversibility line displays weak field dependence between integer matching fields indicating multiple-flux-quanta pinning at holes. We find reduced equilibrium compressibility of the vortex matter at integer matching fields, which is strong evidence for the existence of thermodynamic Mott insulator phases. Shaking with a transverse ac field surprisingly reveals first-order melting that is not shifted with respect to the pristine melting line and that seems to occur within the Mott insulator regions. This melting is understood to be the first-order transition in the bulk of the crystal beneath the surface holes. The transition is visible at the surface, despite the reduced vortex compressibility in the top layer.

Optical absorption measurements are used to probe the spin polarization in the integer and fractional quantum Hall effect regimes. The system is fully spin polarized only at filling factor ν=1 and at very low temperatures (∼40mK). A small change in filling factor (δν ±0.01) leads to a significant depolarization. This suggests that the itinerant quantum Hall ferromagnet at ν=1 is surprisingly fragile against increasing temperature, or against small changes in filling factor.

In this Letter, we study the diffusion properties of photoexcited carriers in coupled quantum wells around the Mott transition. We find that the diffusion of unbound electrons and holes is ambipolar and is characterized by a large diffusion coefficient, similar to that found in p-i-n junctions. Correlation effects in the excitonic phase are found to significantly suppress the carriers' diffusion. We show that this difference in diffusion properties gives rise to the appearance of a photoluminescence ring pattern around the excitation spot at the Mott transition.

We present measurements of optical interband absorption in the fractional quantum Hall regime in a GaAs quantum well in the range 0

Disorder and porosity are parameters that strongly influence the physical behavior of materials, including their mechanical, electrical, magnetic and optical properties. Vortices in superconductors can provide important insight into the effects of disorder because their size is comparable to characteristic sizes of nanofabricated structures. Here we present experimental evidence for a novel form of vortex matter that consists of interconnected nanodroplets of vortex liquid caged in the pores of a solid vortex structure, like a liquid permeated into a nanoporous solid skeleton. Our nanoporous skeleton is formed by vortices pinned by correlated disorder created by high-energy heavy ion irradiation. By sweeping the applied magnetic field, the number of vortices in the nanodroplets is varied continuously from a few to several hundred. Upon cooling, the caged nanodroplets freeze into ordered nanocrystals through either a first-order or a continuous transition, whereas at high temperatures a uniform liquid phase is formed upon delocalization-induced melting of the solid skeleton. This new vortex nanoliquid displays unique properties and symmetries that are distinct from both solid and liquid phases.

Structure, dynamics, and thermodynamic properties of vortex matter in the presence of a low density of columnar defects (CDs) were studied in BSCCO crystals. Magnetic decorations show that when vortices outnumber CDs a heterogeneous vortex matter is formed consisting of two populations of vortices: vortices residing on CDs form a matrix of pinned vortices, whereas the interstitial vortices form ordered crystallites within the 'pores' of the matrix. Differential magneto-optical studies reveal that at elevated fields this porous phase melts in two stages, a first-order melting of the crystallites at a temperature considerably higher than the pristine melting, and a continuous melting of the matrix at still higher temperature. At low fields the two transitions occur simultaneously, giving rise to a sharp kink in the observed melting line.

A low density columnar defects (CD) to perturb the vortex liquid for the formation of an intermediate nanoliquid phase was discussed. For visualising the flow of transport current, the evidence of delocalization line was revealed within the reversible vortex region by using a differential magneto-optical technique. The CD's were created using low irradiation doses of 1 GeV Pb ions. It was found that the nanoliquid phase displayed a high correlation along the columnar defects but no transverse critical currents.

The conventional way of trapping ions is based on the uses of RF or magnetic fields, like in Paul or Penning traps. In such traps the ions are stored with approximately zero kinetic energy. In many applications a well-defined ion beam is needed especially in collision experiment, where the initial direction of a beam is critical for reaction product measurements and a well defined field free region is required at the collision place. In the last few years we have developed a new type of electrostatic ion trap for ion beams of a few keV per charge, with no mass limit. The ions are injected through a stack of electrodes, which are used as an electrostatic mirror. The ions are confined in a region of few tens of centimeters by two electrostatic mirrors, located on opposite sides. The stability criterion of such a trap can be demonstrated to be similar to the one existing for optical resonator. The dynamics of such trapped ion beam was studied for various potentials on the electrostatic mirrors. Two modes of operation where found. In the first mode a self bunching effect was observed where the ion-ion Coulomb interaction generates a single bunch with constant length along the whole trapping time. This mode of operation can be used for Fourier mass spectrometry. A second mode, where the Coulomb interaction enhances the correlation between the ion position and momentum, enables phase space manipulation of the stored ion beam.

We describe the preparation of a sealed gas-filled photomultiplier (GPMT) for the visible spectral range and present the properties of the first prototypes. They consist of a 50 mm diameter semitransparent bialkali (K-Cs-Sb) photocathode coupled to a 30 mm × 30 mm Kapton multi-gas electron multiplier (GEM). High gain of 2 × 10⁴ in two-GEM mode and a quantum efficiency of 13% at 405 nm have been reached at 700 Torr of Ar/CH ₄ (95:5). The detector structure and experimental setup are described; results are presented on the GPMT gain, ion-feedback and its suppression, stability, and other critical parameters in various gas mixtures. Hot sealing techniques with In/Sn and In/Bi solders are discussed.

When vortices outnumber CDs, heterogeneity was taken into account for a proper description of the structure and the thermodynamic behavior of the vortex matter. Evidence was found for two mechanisms: melting of superheated crystallites within the pores of a solid matrix and the destruction of the rigid matrix. The intersection point of these two independent processes resulted in a sharp kink in the observed melting line.

We describe a new mass spectrometric technique that is based on the use of a linear electrostatic ion trap and a newly discovered self-bunching phenomenon. Ions are stored in the trap and their oscillation frequencies are determined by Fourier transform of their oscillation times. Using this system, we demonstrate that it is possible to simultaneously trap several masses and obtain their mass spectra with high resolution. The instrument is compared to time-of-flight mass, as well as to ion cyclotron resonance mass spectrometers.

We present a microscopic understanding of the underlying physics that governs the photoluminescence spectrum at low electron densities. By performing near- and far-field measurements we show how the various characteristics of the spectrum (intensity, energy, width) are affected by the background electron density and the potential fluctuations due to the remote ionized donors.

Vortex matter phase transitions in the high-temperature superconductor Bi₂Sr₂CaCu₂O₈ were studied using local magnetization measurements combined with a vortex 'shaking' technique. The measurements revealed thermodynamic evidence of a first-order transition (FOT) along the second magnetization peak line, at temperatures below the apparent critical point T_cp. We found that the FOT line does not terminate at T_cp, but continues down to at least 30 K. This observation suggests that the ordered vortex lattice phase is destroyed through a unified FOT that changes its character from thermally induced melting at high temperatures to a disorder-induced transition at low temperatures. At intermediate temperatures the transition line shows an upturn, which implies that the vortex matter displays 'inverse' melting behavior.

We demonstrate that the synchronization effect observed [Pedersen et al., Phys. Rev. Lett. 87, 055001 (2001)], when a bunch of ions oscillates between two mirrors in an electrostatic ion beam trap, can be explained as a negative mass instability. We derive simple necessary conditions for the existence of a regime in which this dispersionless behavior occurs and demonstrate that in this regime, the ion trap can be used as a high resolution mass spectrometer.

Inverse melting is the process in which a crystal reversibly transforms into a liquid or amorphous phase when its temperature is decreased. Such a process is considered to be very rare¹, and the search for it is often hampered by the formation of non-equilibrium states or intermediate phases². Here we report the discovery of first-order inverse melting of the lattice formed by magnetic flux lines in a high-temperature superconductor. At low temperatures, disorder in the material pins the vortices, preventing the observation of their equilibrium properties and therefore the determination of whether a phase transition occurs. But by using a technique³ to 'dither' the vortices, we were able to equilibrate the lattice, which enabled us to obtain direct thermodynamic evidence of inverse melting of the ordered lattice into a disordered vortex phase as the temperature is decreased. The ordered lattice has larger entropy than the low-temperature disordered phase. The mechanism of the first-order phase transition changes gradually from thermally induced melting at high temperatures to a disorder-induced transition at low temperatures.

General arguments suggest that first-order phase transitions become less sharp in the presence of weak disorder, while extensive disorder can transform them into second-order transitions; but the atomic level details of this process are not clear. The vortex lattice in superconductors provides a unique system in which to study the first-order transition on an inter- particle scale, as well as over a wide range of particle densities. Here we use a differential magneto-optical technique to obtain direct experimental visualization of the melting process in a disordered superconductor. The images reveal complex behaviour in nucleation, pattern formation, and solid- liquid interface coarsening and pinning. Although the local melting is found to be first-order, a global rounding of the transition is observed; this results from a disorder-induced broad distribution of local melting temperatures, at scales down to the mesoscopic level. We also resolve local hysteretic supercooling of microscopic liquid domains, a non-equilibrium process that occurs only at selected sites where the disorder-modified melting temperature has a local maximum. By revealing the nucleation process, we are able to experimentally evaluate the solid-liquid surface tension, which we find to be extremely small.

We study the spatial distribution of the photoluminescence of a gated two-dimensional electron gas with sub-wavelength resolution. This is done by scanning a tapered optical fibre tip with an aperture of 250 nm in the near field region of the sample surface, and collecting the photoluminescence. The spectral line of the negatively charged exciton, formed by binding of a photo-excited electron-hole pair to an electron, serves as an indicator for the local presence of charge. The local luminescence intensity of this line is directly proportional to the number of electrons under the tip. We observe large spatial fluctuations in this intensity in the gate voltage range, where the electron conductivity exhibits a sharp drop. The amplitude of these fluctuations increases and the Fourier spectrum extends to lower spatial frequencies as the gate voltage becomes more negative. We show that the fluctuations are due to the statistical distribution of localised electrons in the random potential of the remote ionised donors. We use these fluctuations to image the electron and donor distribution in the plane.

A new ion trap for storing fast (keV) ion beams is presented. The trap, which is electrostatic, stores the ions between two electrostatic mirrors. Two different examples of utilization of the trap are given. The first one required the extraction of the trapped particles after storage, in order to study their collision with an external target, while the second example measured the lifetime of the mestastable He- levels. The advantage of storage using pure electrostatic fields is discussed.

The synthesis of a pure phase of very long and hollow WS₂ nanotubes from short but asymmetric oxide nanoparticles is described. In this process, the oxide nanoparticles grow along their longest axis; and subsequently their outermost layer is being sulfidized, while the growing oxide tip remains uncoated as long as the nanowhisker continues to grow. Thereafter, the sulfide cup is closed and a slow diffusion controlled sulfidization of the oxide core is completed within 60-120 min.

The first-order phase transition of the vortex-lattice in Bi2Sr2CaCu2O8 crystals is shown to transform into a continuous transition when disorder is introduced via a very low concentration of columnar defects. We demonstrate fine tuning of the disorder strength and the recovery of the first-order transition by varying the concentration of the columns, by changing the temperature along the melting line, or by tilting the magnetic field with respect to the columns.

One of the most common investigation techniques of type-II superconductors is the transport measurement, in which an electrical current is applied to a sample and the corresponding resistance is measured as a function of temperature and magnetic field, At temperatures well below the critical temperature, T-c, the resistance of a superconductor is usually immeasurably low, But at elevated temperatures and fields, in the so-called vortex liquid phase, a substantial linear resistance is observed(1). In this dissipative state, which in anisotropic high-temperature superconductors like Bi2Sr2CaCu2O8 may occupy most of the mixed-state phase diagram, the transport current is usually assumed to flow uniformly across the sample as in a normal metal. To test this assumption, we have devised a measurement approach which allows determination of the flow pattern of the transport current across the sample. The surprising result is that, in Bi2Sr2CaCu2O8 crystals, most of the current flows at the edges of the sample rather than in the bulk, even in the highly resistive state, due to the presence of strong surface barriers, This finding has significant implications for the interpretation of existing resistivity data and may be of importance for the development of high-temperature superconducting wires and tapes.

The vortex matter phase diagram of Bi₂Sr₂CaCu₂O₈ crystals is analyzed by investigating vortex penetration through the surface barrier in the presence of a transport current. The strength of the effective surface barrier and its nonlinearity and asymmetry are used to identify a possible new ordered phase above the first-order transition. This technique also allows sensitive determination of the depinning temperature. The solid phase below the first-order transition is apparently subdivided into two phases by a vertical line extending from the multicritical point.

Self-assembly (SA) of long-chain alkanethiols on copper was studied. Two factors were found to have substantial influence on the SA process: (i) the chemical reactivity of Cu toward substances present in the adsorption solution, particularly the solvent, and (ii) surface pretreatment, which influences the amount of oxide and the surface morphology. Both factors are less important in the case of SA onto gold because of its chemical inertness. Monolayers of octadecanethiol (C18SH) were adsorbed from different solvents (ethanol, toluene, and bicyclohexyl) at various thiol concentrations onto Cu surfaces pretreated in several different ways. The monolayers were characterized by contact-angle measurements, grazing-incidence Fourier transform infrared spectroscopy, and scanning force microscopy. Ethanol, the most common solvent for alkanethiol SA, is found to have a negative effect on monolayer SA apparently because of its chemical reactivity toward copper. With toluene as a solvent, better oriented and more crystalline monolayers are obtained provided that a higher thiol concentration is used to compensate for the higher solubility of thiols in toluene. Treatment of the Cu surface prior to SA is shown to significantly improve the SA by reducing the amount of surface oxide and the surface corrugation. The effect of the solvent is more critical than surface oxidation; hence, high-quality monolayers are formed in the presence of thin oxide layers on Cu surfaces. Superior C18SH monolayers, in terms of organization and crystallinity, are obtained by SA from toluene onto Cu surfaces sputtered-annealed in high vacuum, even when the Cu surface is subjected to short exposure to air before SA.

A new technique for trapping of fast (keV) ion beams is presented. The trap, which is electrostatic, works on a principle similar to that of optical resonators. The main advantages of the trap are the possibility to trap fast beams without need of deceleration, the well-defined beam direction, the easy access to the trapped beam by various probes, and the simple requirement in terms of external beam injection. Results of preliminary experiments related to the radiative cooling of molecular ions are also reported.

A technique for storage of fast-ion beams (keV) using only electrostatic fields is presented. The fast-ion trap is designed like an optical resonator, whose electrode configuration allows for a very large field-free region, easy access into the trap by various probes, a simple ion loading technique, and a broad acceptance range for the initial kinetic energies of the ions. Such a fast-ion storage device opens up many experimental possibilities, a few of which are presented.

YBa2Cu3O7 (1237) was reduced and reoxidized at room temperature (RT), by using wet electrochemistry to extract, or solid state electrochemistry to re-insert oxygen. With thin films this led to homogeneous products, as judged by X ray diffraction and temperature dependence of electrical resistivity. Because reduction leads to loss of superconductivity and re-oxidation restores it, this method allows room temperature control over superconducting properties of (parts of) films and, thus, can be used for patterning of (1237) thin films. We showed this by preparing SNS-like structures by this method. The method affords control not only over bulk properties, but also over the quality of the intergranular contact, possibly via control of oxygen concentration and ordering in the outermost layers of grains (in films and pellets). The results imply rapid, field-assisted, oxygen motion and this was confirmed by independent measurements.

YBa₂Cu₃O₇ (1237) was reduced and reoxydated quantitatively, in a controlled manner, at room temperature (RT), by way of extraction or insertion of oxygen, using an electrochemical set-up. RT reduction and reoxygenation of thin films, which led to homogeneous products, as judged by X ray diffraction. Since reduction leads to loss of superconductivity and re-oxidation restores it, this method allows room temperature control over superconducting properties of (parts of) films. This permits patterning of (1237) thin films. SNS-like structures were already prepared by this method. The method affords control not only over n(E_F) via [oxygen]_bulk, but also over the quality of the intergranular contact, possibly via control of [oxygen] in the outermost layers of grains (in films and pellets).

The oxygen content of polycrystalline samples of YBa₂Cu₃O_{7 – x} can be reduced quantitatively, in a controlled fashion, by electrochemical techniques at room temperature in propylene carbonate. Upon reduction, the propylene carbonate undergoes an unusual reaction at the YBa₂Cu₃O_{7 – x} cathode to produce propanal, apparently because of the production of an active oxygen species on the surface. The reduced materials have been characterized by X-ray powder diffraction, electrical resistivity and magnetic susceptibility. The large-grained, reduced pellets are found to be inhomogeneous with respect to x. The reduced materials exhibit a broadened transition to the superconducting state. This effect is ascribed to the formation of metastable phases formed during reduction. After a low-temperature anneal, 80, 60 and 20 K transition temperatures are observed. These results indicate that T_c is a continuous function of oxygen content, but a discontinuous function of oxygen ordering.

The oxygen content of YBa₂Cu₃O₇-x can be reduced at room temperature using a liquid electrolyte. The degree of reduction can be controlled by coulometry. The products have been characterized structurally, magnetically and electrically. Reduction broadens the transition to the superconducting state. Two distinct superconducting phases are observed only upon annealing at 300°C. Thus while reduction alone affects the T_c, the distinct lower T_c phase is a result of ordering on the oxygen sublattice.

The oxygen content of YBa₂Cu₃O_7-xcan be reduced electrochemically in a non-aqueous electrolyte at room temperature. The products are characterized by X-ray powder diffraction, magnetic susceptibility and electrical conductivity. The transition to the superconducting state is broadened upon reduction. Subsequent annealing of the reduced samples yields materials with distinct 90, 60 and 20 K transitions. These results indicate that the oxygen content is the primary factor in controlling T_c.