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Yuval Gefen

Publications and source records attributed to Yuval Gefen.

6 recordsLinked to original sources
PubMed2006

Interplay of spin and charge channels in zero-dimensional systems.

We study the interplay of charge and spin (zero-mode) channels in quantum dots. The latter affects the former in the form of a distinct signature on the differential conductance. We also obtain both longitudinal and transverse spin susceptibilities. All these observables, underlain by spin fluctuations, become accentuated as one approaches the Stoner instability. The nonperturbative effects of zero-mode interaction are described in terms of the propagation of gauge bosons associated with charge [U(1)] and spin [SU(2)] fluctuations in the dot, while transverse spin fluctuations are analyzed perturbatively.

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PubMed2005

Quasiparticle tunneling through a barrier in the fractional quantum hall regime.

Tunneling of fractionally charged quasiparticles (QPs) through a barrier is considered in the context of a multiply connected geometry. In this geometry global constraints do not prohibit such a tunneling process. The tunneling amplitude is evaluated and the crossover from mesoscopic QP-dominated to electron-dominated tunneling as the system's size is increased is found. The presence of disorder enhances both electron and QP-tunneling rates.

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PubMed2005

Geometric nature of the environment-induced Berry phase and geometric dephasing.

We investigate the geometric phase or Berry phase acquired by a spin half which is both subject to a slowly varying magnetic field and weakly coupled to a dissipative environment (either quantum or classical). We study how this phase is modified by the environment and find that the modification is of a geometric nature. While the original Berry phase (for an isolated system) is the flux of a monopole field through the loop traversed by the magnetic field, the environment-induced modification of the phase is the flux of a quadrupolelike field. We find that the environment-induced phase is complex, and its imaginary part is a geometric contribution to dephasing. Its sign depends on the direction of the loop. Unlike the Berry phase, this geometric dephasing is gauge invariant for open paths of the magnetic field.

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PubMed2005

Theory of charge sensing in quantum-dot structures.

Charge sensing in quantum-dot structures is studied by an exactly solvable reduced model and numerical density-matrix renormalization-group methods. Charge sensing is characterized by repeated cycling of the occupation of current-carrying states due to the capacitive coupling to trap states. In agreement with recent experiments, it results in characteristic asymmetric Coulomb-blockade peaks as well as sawtooth and domelike structures. Temperature introduces asymmetric smearing of these features and correlations in the conductance provide a fingerprint of charge sensing.

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PubMed2003

Berry phase in a nonisolated system.

We investigate the effect of the environment on a Berry phase measurement involving a spin-half. We model the spin + environment using a biased spin-boson Hamiltonian with a time-dependent magnetic field. We find that, contrary to naive expectations, the Berry phase acquired by the spin can be observed, but only on time scales which are neither too short nor very long. However this Berry phase is not the same as for the isolated spin-half. It does not have a simple geometric interpretation in terms of the adiabatic evolution of either bare spin states or the dressed spin resonances. This result is crucial for proposed Berry phase measurements in superconducting nanocircuits.

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