arXiv subjects

Yuval Gefen

Publications and source records attributed to Yuval Gefen.

193 records · Page 11Linked to original sources

arXiv1998

Level statistics of quantum dots coupled to reservoirs

We study the effect of electron tunneling on the level statistics of quantum dots. While the coupling between individual levels and the electron reservoir leads predominantly to the expected level broadening, the indirect coupling of adjacent levels via the reservoir results in a new asymptotic level statistics and broadening. These features, which are attributed to renormalized spectral weights rather than renormalized eigenvalues of the Hamiltonian, are observable in the asymptotic frequency dependence in an absorption experiment.

cond-mat.mes-hall↗

arXiv1997

Charge Fluctuations in a Quantum Dot with a Dissipative Environment

We consider a multiple tunneling process into a quantum dot capacitively coupled to a dissipative environment. The problem is mapped onto an anisotropic Kondo model in its Coulomb gas representation. The tunneling barrier resistance and the dissipative resistance of the environment correspond to the transverse and the longitudinal Kondo couplings respectively. We thus identify a line in the parameter space of the problem which corresponds to a zero-temperature Berezinskii-Kosterlitz-Thouless like phase transition. The physics of coupling to the environment is elucidated and experimental consequences of the predicted transition are discussed.

cond-mat.mes-hall↗

arXiv1997

Statistical Ensembles and Spectral Correlations in Mesoscopic Systems

Employing different statistical ensembles may lead to qualitatively different results concerning averages of physical observables on the mesoscopic scale. Here we discuss differences between the canonical and the grandcanonical ensembles due to both quenched disorder and thermodynamical effects. We show how these differences are related to spectral correlations of the system at hand, and evaluate the conditions (temperature, system's size) when the thermodynamic limit is achieved. We demonstrate our approach by evaluating the heat capacity, persistent currents and the occupation probability of single electron states, employing a systematic diagrammatic approach.

cond-mat.mes-hall↗

arXiv1996

Differences between Statistical Mechanics and Thermodynamics on the Mesoscopic Scale

We present a systematic expansion in the ratio between the level spacing and temperature and employ it to evaluate differences between statistical mechanics and thermodynamics in finite disordered systems. These differences are related to spectral correlations in those systems. They are fairly robust and are suppressed at temperatures much higher than the level spacing.

cond-mat↗

arXiv1996

Electron Scattering Through a Quantum Dot: A Phase Lapse Mechanism

The scattering phase shift of an electron transferred through a quantum dot is studied within a model Hamiltonian, accounting for both the electron--electron interaction in the dot and a finite temperature. It is shown that, unlike in an independent electron picture, this phase may exhibit a phase lapse of $ π$ {\em between } consecutive resonances under generic circumstances.

cond-mat↗

arXiv1996

Zero--Bias Anomaly in Finite Size Systems

The small energy anomaly in the single particle density of states of disordered interacting systems is studied for the zero dimensional case. This anomaly interpolates between the non--perturbative Coulomb blockade and the perturbative limit, the latter being an extension of the Altshuler--Aronov zero bias anomaly at d=0. Coupling of the zero dimensional system to a dissipative environment leads to an effective screening of the interaction and a modification of the density of states.

cond-mat↗

arXiv1995

What is the Thouless Energy for Ballistic Systems?

The Thouless energy, $\Ec$ characterizes numerous quantities associated with sensitivity to boundary conditions in diffusive mesoscopic conductors. What happens to these quantities if the disorder strength is decreased and a transition to the ballistic regime takes place? In the present analysis we refute the intuitively plausible assumption that $\Ec$ loses its meaning as an inverse diffusion time through the system at hand, and generally disorder independent scales take over. Instead we find that a variety of (thermodynamic) observables are still characterized by the Thouless energy.

cond-mat↗

arXiv1995

From the Zero--bias Anomaly to the Coulomb Blockade: an Exactly Solvable Model.

A microscopic theory of zero wavelength (q=0) interaction in finite--size systems is proposed. Its exact solution interpolates between the Coulomb blockade and the perturbative Altshuler--Aronov theory, in the strong and weak interaction limits respectively. The tunneling density of states and the quasiparticle life--time are calculated. The physical nature of the q=0 component of the interaction is discussed.

cond-mat↗

arXiv1994

Universal Conductance Distribution in the Quantum Size Regime

We study the conductance (g) distribution function of an ensemble of isolated conducting rings, with an Aharonov--Bohm flux. This is done in the discrete spectrum limit, i.e., when the inelastic rate, frequency and temperature are all smaller than the mean level spacing. Over a wide range of g the distribution function exhibits universal behavior P(g)\sim g^{-(4+β)/3}, where β=1 (2) for systems with (without) a time reversal symmetry. The nonuniversal large g tail of this distribution determines the values of high moments.

cond-mat↗

arXiv1994

Magnetization of Disordered Ballistic Quantum Billards

We study the magnetic response of mesoscopic quantum dots in the ballistic regime where the mean free path $l_e$ is larger that the size $L$ of the sample, yet smaller than $L (k_F L)^{d-1}$. In this regime, disorder plays an important role. Employing a semiclassical picture we calculate the contribution of long trajectories which are strongly affected by static disorder and which differ sharply from those of clean systems. In the case of a magnetic field, they give rise to a large linear paramagnetic susceptibility (which is disorder independent), whose magnitude is in agreement with recent experimental results. In the case of a Aharonov-Bohm flux, the susceptibility is disorder dependent and is proportional to the mean free path as in the diffusive regime. We also discuss the corresponding non--linear susceptibilities.

cond-mat↗

arXiv1994

Magnetic Response of Disordered Ballistic Quantum Dots

The weak field average magnetic susceptibility of square shaped mesoscopic conductors is studied within a semiclassical framework. Long semiclassical trajectories are strongly affected by static disorder and differ sharply from those of clean systems. They give rise to a large linear paramagnetic susceptibility which is disorder independent and in agreement with recent experiments. The crossover field to a nonlinear susceptibility is discussed.

cond-mat↗

arXiv1993

Conductance of Aharonov--Bohm Rings: From the Discrete to the Continuous Spectrum Limit

The dissipative conductance of an array of mesoscopic rings, subject to an a.c. magnetic flux is investigated. The magneto--conductance may change sign between canonical and grand-canonical statistical ensembles, as function of the inelastic level broadening and as function of the temperature. Differences between canonical and grand-canonical ensembles persist up to temperature of the order of the Thouless energy.

cond-mat↗

arXiv1993

Phi_0 - Periodic Aharonov-Bohm Oscillations Survive Ensemble Averaging

We have demonstrated that Phi_0 periodic Aharonov--Bohm oscillations measured in a ensemble of rings may survive after ensemble averaging procedure. The central point is the difference between the preparation stage of the ensemble and the subsequent measurement stage. The robustness of the effect under finite temperature and non--zero charging energy of rings is discussed.

cond-mat↗