Research
Introduction
After
spending a few years at Princeton
University, where I have been a Ph.D. student and a postdoc in Prof.
Dan Tsui's lab,
I am very excited about starting our experimental effort here at the
Weizmann Institute.
As I have joined an ongoing effort, my landing has been be softer than
usual, and I am already deeply involved in research.
My main experience is in low-temperature
transport experiments. The facilities in my lab include a top-loading,
Oxford-made, dilution refrigerator
allowing us to experiment down to 10 mK (!). It is equipped with superconducting
magnets capable of 14 Tesla. I put a strong emphasis on hands-on experience
for the students, so all the maintenance and support is done by us.
I am looking for Ph.D. and Master
students student to join our effort at the Weizmann Institute. There
are many possibilities for research in our field and I will not restrict
the students to any particular agenda. However, to get started it is
sometimes helpful to keep a particular project in mind (at least until
it becomes clear that it leads nowhere...). Below I list three such
projects.
1. Mesoscopic
Transport Near The Critical Point of Quantum Phase Transitions:
This project will mainly deal with
mesoscopic effects near the critical point of quantum phase transitions
(QPT's). Mesoscopic effects were used extensively in the past
as a diagnostic tool to provide information on quantum-transport characteristics.
The project at hand will utilize this aspect of mesoscopics to directly
probe quantum-coherence near a QPT.
We will study two kinds of transitions
that complement each other in a surprising and puzzling manner.
The first is the quantum Hall-to-Insulator
transition, which is observed in two-dimensional electron systems
at high magnetic fields. This transition has attained the status
of `system of choice' for studying QPT's, and continues to supply new
and interesting results. In parallel, we will study the superconductor-insulator
transition. The material we chose, amorphous InO, was used in
both disorder-driven and magnetic field-driven transitions. We
will prepare small, mesoscopic, samples out of both InO films and semiconductor
materials to conduct size-dependent studies. In addition, we will
fabricate Aharonov-Bohm rings to study interference effects which is
the standard tool for investigating quantum-coherent transport.
Last, but not least, we will perform low-frequency noise measurements
in mesoscopic, as well as macroscopic, samples near a QPT.
A complementary study of mesoscopic
effects near a QPT in the two types of transitions will address a central
issue pertinent to our understanding of QPT's: Whether transport in
their vicinity can, in realistic samples and measurement conditions,
be described as a quantum-mechanical, phase-coherent process or, as
suggested by recent theories (and perhaps even by recent experiments),
electron-electron interactions inevitably lead to diminished coherence
near the critical point. At any rate, the proposed experiments are interesting
in their own right and do not hinge upon embracing a particular theoretical
framework.
2. Superconductor-Insulator
in Two-Dimensions
3. Mesoscopics
of Highly Interacting Systems
One way the theorists find out of
their possibly erroneous conviction that there should be no metals in
2D is that their arguments were based on a single-electron, non-interacting
picture. Now, surprisingly enough, the non-interacting picture works
very well for metals. This is because in metals, the fermi energy (Ef)
is very high relative to the strength of the electron-electron interaction
energy (Ec). However, in modern semiconductor devices, it is possible
to go to the other extreme, where Ec>Ef. Then it is expected that
interactions will dominate the physics (strong interactions is one of
the common features of the family of samples that exhibit the metal-insulator
transition in 2D). I am glad to announce that the samples that are grown
here at the center (by Hadas Shtrikman) hold the world record in the
Ec/Ef ratio in 2D semiconductors. We will use these samples to fabricate
mesoscopic structures such as quantum dots and Aharonov-Bohm rings.
Working in this new regime we expect different physics from what was
previously seen in standard mesoscopic structures.
Previous
projects:
This project
was initiated by Yael
Hanein here at the center. Using a newly developed ISIS
semiconductor structure, it is possible to control the carrier density
in the two-dimensional (2D) layer over a very wide range. With this
flexibility we can transform the low-temperature behavior from a conductor
to an insulator. It would not be very exciting but for the fact that
for nearly 2 decades it was held very strongly by theorists (headed
by Phil
Anderson) that a two-dimensional system cannot be metallic. The
initial discovery , in Si-MOSFET's, of a metallic-like phase in a 2D
system was accepted with a lot of skepticism by the community. Yael's
observation of a similar behavior in high-quality GaAs helped making
this effect mainstream.