Publications

1998

1. Direct observation of a fractional charge

   de-Picciotto R., Reznikov M., Heiblum M., Umansky V. Y., Bunin G. & Mahalu D. (1998) Physica B. 251, p. 395-400  Abstract

   The charge of quasi-particles in the fractional quantum Hall regime was determined via quantum shot noise measurements. The noise is generated by a current flow through a partially transmitting quantum point contact in a two dimensional electron gas and is directly proportional to the charge of the quasi-particles. We measured quantum shot noise at a filling factor of 1/3 and found that the charge of the quasi-particles is e/3 as predicted by Laughlin. (C) 1998 Elsevier Science B.V. All rights reserved.

   Arxiv: 9707289
2. Dephasing in electron interference by a 'which-path' detector

   Buks E., Schuster R., Heiblum M., Mahalu D. & Umansky V. Y. (1998) Nature. 391, 6670, p. 871-874  Abstract

   Wave-particle duality, as manifest in the two-slit experiment, provides perhaps the most vivid illustration of Bohr's complementarity principle: wave-like behaviour (interference) occurs only when the different possible paths a particle can take are indistinguishable, even in principle. The introduction of a which-path (welcher Weg) detector for determining the actual path taken by the particle inevitably involved coupling the particle to a measuring environment, which in turn results in dephasing (suppression of interference). In other words, simultaneous observations of wave and particle behaviour is prohibited. Such a manifestation of the complementarity principle was demonstrated recently using a pair of correlated photons, with measurement of one photon being used to determine the path taken by the other and so prevent single-photon interference. Here we report the dephasing effects of a which path detector on electrons traversing a double-path interferometer. We find that by varying the sensitivity of the detector we can affect the visibility of the oscillatory interference signal, thereby verifying the complementarity principle for fermions.

3. From the kondo regime to the mixed-valence regime in a single-electron transistor

   Goldhaber-Gordon D., Gores J., Kastner M., Shtrikman H., Mahalu D. & Meirav U. (1998) Physical review letters. 81, 23, p. 5225-5228  Abstract

   We demonstrate that the conductance through a single-electron transistor at low temperature is in quantitative agreement with predictions of the equilibrium Anderson model. The Kondo effect is observed when an unpaired electron is localized within the transistor. Tuning the unpaired electrons energy toward the Fermi level in nearby leads produces a crossover between the Kondo and mixed-valence regimes of the Anderson model.

4. Kondo effect in a single-electron transistor

   Goldhaber-Gordon D., Shtrikman H., Mahalu D., Abusch-Magder D., Meirav U. & Kastner M. (1998) Nature. 391, 6663, p. 156-159  Abstract

   How localized electrons interact with delocalized electrons is a central question to many problems in solid-state physics. The simplest manifestation of this situation is the Kondo effect, which occurs when an impurity atom with an unpaired is placed in a metal. At low temperatures a spin singlet state is formed between the unpaired localized electrons at the Fermi energy. Theories predict that a Kondo singlet should form in a single-electron transistor (SET), which contains a confirmed 'droplet' of electrons coupled by quantum-mechanical tunnelling to the delocalized electrons in the transistor's leads. If this is so, a SET could provide a means of investigating aspects of the Kondo effect under controlled circumstances that are not accessible in conventional systems: the number of electron can be changed from odd to even, the difference in energy between the localized state and the Fermi level can be turned, the coupling to the leads can be adjusted, voltage differences can be applied to reveal non-equilibrium Kondo phenomena, and a single localized state can be studied rather than a statistical distribution. But for SETs fabricated previously, the binding energy of the spin singlet has been too small to observe Kondo phenomena. Ralph and Buhrman have observed the Kondo singlet at a single accidental impurity in a metal point contact, but with only two electrodes and without control over the structure they were not able to observe all of the features predicted. Here we report measurements on SETs smaller than those made previously, which exhibit all of the predicted aspects of the Kondo effect in such a system.