arXiv subjects

Efrat Shimshoni

Publications and source records attributed to Efrat Shimshoni.

60 records · Page 4Linked to original sources

arXiv1998

Edge States on a Quantum Hall Liquid--Solid Interface

We study the edge--states excitations of a droplet of quantum Hall liquid embedded in an electron (Wigner) solid. The presence of strong correlations between the liquid and solid sectors in the ground state is shown to be reflected in the density of states $D(E)$, associated with the excitations of the liquid--solid interface. We find that the prominent effect of these correlations is a suppression of $D(E)$ with respect to its value ($D_0(E)$) in the absence of the Wigner solid environment: $D(E) \sim e^{-α|E|}D_0(E)$. The coefficient $α$ (which is shown to vanish for a perfectly regular distribution of electron sites in the solid), is evaluated for two different realizations of an irregular distribution. We conclude that probing this effect (e.g. in a tunneling experiment), can provide evidence for correlated liquid--solid mixture states in quantum dots, or disordered samples, in very strong magnetic fields.

cond-mat.mes-hall↗

arXiv1997

Transport Through Quantum Melts

We discuss superconductor to insulator and quantum Hall transitions which are first order in the clean limit. Disorder creates a nearly percolating network of the minority phase. Electrical transport is dominated by tunneling or activation through the saddle point junctions, whose typical resistance is calculated as a function of magnetic field. In the Boltzmann regime, this approach yields resistivity laws which agree with recent experiments in both classes of systems. We discuss the origin of dissipation at zero temperature.

cond-mat.mes-hall↗

arXiv1997

Coulomb Drag at the Onset of Anderson Insulators

It is shown that the Coulomb drag between two identical layers in the Anderson insulting state indicates a striking difference between the Mott and Efros-Shklovskii (ES) insulators. In the former, the trans-resistance $ρ_t$ is monotonically increasing with the localization length $ξ$; in the latter, the presence of a Coulomb gap leads to an opposite result: $ρ_t$ is enhanced with a decreasing $ξ$, with the same exponential factor as the single layer resistivity. This distinction reflects the relatively pronounced role of excited density fluctuations in the ES state, implied by the enhancement in the rate of hopping processes at low frequencies. The magnitude of drag is estimated for typical experimental parameters in the different cases. It is concluded that a measurement of drag can be used to distinguish between interacting and non-interacting insulating state.

cond-mat↗

arXiv1996

The Quantized Hall Insulator

We model the insulator neighboring the 1/k quantum Hall phase by a random network of puddles of filling fraction 1/k. The puddles are coupled by weak tunnel barriers. Using Kirchoff's laws we prove that the macroscopic Hall resistivity is quantized at $k h/ e^2$ and independent of magnetic field and current bias -- in agreement with recent experimental observations. In addition, for k>1 this theory predicts non linear longitudinal response $V\sim I^α$ at zero temperature, and $V/I\sim T^{1-{1\over α}}$ at low bias. $α$ is determined using Renn and Arovas' theory for the single junction response, and is related to the Luttinger liquid spectra of the edge states straddling the typical tunnel barrier. The dependence of $V(I)$ on the magnetic field is related to the typical puddle size. Deviations of $V(I)$ from a pure power law are estimated using a series/parallel approximation for the two dimensional random nonlinear resistor network. We check the validity of this approximation by numerically solving for a finite square lattice network.

cond-mat↗

arXiv1995

The Role of Vortices in the Mutual Coupling of Superconducting and Normal-Metal Films

I propose a possible explanation to a recently observed ``cross-talk'' effect in metal-insulator-metal trilayers, indicating a sharp peak near a superconducting transition in one of the metal films. Coulomb interactions are excluded as a dominant coupling mechanism, and an alternative is suggested, based on the local fluctuating electric field induced by mobile vortices in the superconducting layer. This scenario is compatible with the magnitude of the peak signal and its shape; most importantly, it addresses the {\it non-reciprocity} of the effect in exchanging the roles of the films.

cond-mat↗

arXiv1993

The Quantum Hall Effect in Drag: Inter-layer Friction in Strong Magnetic Fields

We study the Coulomb drag between two spatially separated electron systems in a strong magnetic field, one of which exhibits the quantum Hall effect. At a fixed temperature, the drag mimics the behavior of $σ_{xx}$ in the quantum Hall system, in that it is sharply peaked near the transitions between neighboring plateaux. We assess the impact of critical fluctuations near the transitions, and find that the low temperature behavior of the drag measures an exponent $η$ that characterizes anomalous low frequency dissipation; the latter is believed to be present following the work of Chalker.

cond-mat↗