12 research outputs found
Phase Relaxation of Electrons in Disordered Conductors
Conduction electrons in disordered metals and heavily doped semiconductors at
low temperatures preserve their phase coherence for a long time: phase
relaxation time can be orders of magnitude longer than the momentum
relaxation time. The large difference in these time scales gives rise to well
known effects of weak localization, such as anomalous magnetoresistance. Among
other interesting characteristics, study of these effects provide quantitative
information on the dephasing rate . This parameter is of
fundamental interest: the relation between and the
temperature (a typical energy scale of an electron) determines how well a
single electron state is defined. We will discuss the basic physical meaning of
in different situations and its difference from the energy
relaxation rate. At low temperatures, the phase relaxation rate is governed by
collisions between electrons. We will review existing theories of dephasing by
these collisions or (which is the same) by electric noise inside the sample. We
also discuss recent experiments on the magnetoresistance of 1D systems: some of
them show saturation of at low temperatures, the other do not. To
resolve this contradiction we discuss dephasing by an external microwave field
and by nonequilibrium electric noise.Comment: Order of figures and references corrected; one reference added; 15
pages, 2 figures, lecture given on 10th International Winterschool on New
Developments in Solid State Physics, Mauterndorf, Salzburg, Austria; 23-27
Feb. 199
Shot noise in normal metal-d-wave superconducting junctions
We present theoretical calculations and predictions for the shot noise in
voltage biased junctions of superconductors and normal metal
counter-electrodes. In the clean limit for the d-wave superconductor the shot
noise vanishes at zero voltage because of resonant Andreev reflection by
zero-energy surface bound states. We examine the sensitivity of this resonance
to impurity scattering. We report theoretical results for the magnetic field
dependence of the shot noise, as well the fingerprints of subdominant - and
pairing channels.Comment: 15 pages, 8 figures and 3 tables embedde
Dimensional Crossover of Localisation and Delocalisation in a Quantum Hall Bar
The 2-- to 1--dimensional crossover of the localisation length of electrons
confined to a disordered quantum wire of finite width is studied in a
model of electrons moving in the potential of uncorrelated impurities. An
analytical formula for the localisation length is derived, describing the
dimensional crossover as function of width , conductance and
perpendicular magnetic field . On the basis of these results, the scaling
analysis of the quantum Hall effect in high Landau levels, and the
delocalisation transition in a quantum Hall wire are reconsidered.Comment: 12 pages, 7 figure