Microscopic Features of Bosonic Quantum Transport and Entropy Production

The microscopic features of bosonic quantum transport in a nonequilibrium steady state, which breaks time reversal invariance spontaneously, are investigated. The analysis is based on the probability distributions, generated by the correlation functions of the particle current and the entropy production operator. The general approach is applied to an exactly solvable model with a point‐like interaction driving the system away from equilibrium. The quantum fluctuations of the particle current and the entropy production are explicitly evaluated in the zero frequency limit. It is shown that all moments of the entropy production distribution are non‐negative, which provides a microscopic version of the second law of thermodynamics. On this basis a concept of efficiency, taking into account all quantum fluctuations, is proposed and analyzed. The role of the quantum statistics in this context is also discussed.     

Correlated electron states at level crossings of bilayer two-dimensional electron systems in tilted magnetic fields

We have measured the energy-level structure of high mobility, strongly coupled bilayer two-dimensional electron systems in tilted magnetic fields by means of magnetotransport experiments. At tilt angles where single-particle levels with opposite spin and symmetry cross, we observe a surprising sudden broadening of the quantum Hall plateaus and a deepening of the Shubnikov–de Haas minima. This observation is explained by an interaction-induced rearrangement of the energy level structure which strongly increases the energetic splitting of two (anti-)crossing levels.     

Super-Toda theories and W-algebras from superspace Wess-Zumino-Witten models

Using a superspace approach, it is proved that aN=1 Super-Toda theory can be seen as a constrained WZW model based on a supergroup. The gauge transformations which survive the constraints are then usedà la Drinfeld Sokolov to determine explicity the super-W algebra underlying this theory. The conformal spin content of any such super-Walgebra is provided in the general case.URA 14-36 du CNRS, associée à l'E.N.S. de Lyon, et au L.A.P.P.     

Structure of basic Lie superalgebras and of their affine extensions

We generalize to the case of superalgebras several properties of simple Lie algebras involving the use of Dynkin diagrams. If to a simple Lie algebra can be associated one Dynkin diagram, it is a finite set of nonequivalent ones which can be constructed for a basic superalgebra (or B.S.A.). The knowledge of these diagrams, which can be obtained for each B.S.A. in a systematic way, allows us to deduce the regular subsuperalgebras of a B.S.A. The symmetries of the Dynkin diagrams are related to outer automorphisms of B.S.A. and lead to some singular subsuperalgebras. Finally we consider the extended Dynkin diagrams in order to classify the affine B.S.A. and use their symmetries to construct the twisted basic superalgebras.     

Hydrogen chemisorption on cleavage faces of III–V compounds

In this paper a number of experimental results dealing with the study of the electronic properties of H-exposed III–V semiconductor cleavage surfaces will be reviewed. The principal aim of the paper is to show how surface sensitive spectroscopies like electron energy loss spectroscopy (EELS) and ultraviolet photoemission spectroscopy (UPS) can be used to investigate these systems. The paper is focused on GaAs(1 1 0):H. GaAs(1 1 0) is one of the most widely investigated and better known semiconductor surfaces: this system can be taken as a case study for the interaction of H with III–V semiconductor cleavage surfaces. The paper is divided into two parts. In the first part EELS and UPS are used and combined to get information about the surface valence states. In the second part core level (CL) photoemission results are presented and discussed.

Combining theory with the above results, a unified picture of the H interaction with the (1 1 0) surface of GaAs comes out. H atoms chemisorb at the early stages along the dangling bond directions of the ideal not relaxed surface, removing the surface relaxation and introducing at the same time defects at the surface.

At the same time the interaction with H produces a Ga enrichment at the surface ascribed to As desorption.     

Connected subgroups of the poincare group II

The determination, up to a conjugation of connected subgroups of the Poincaré group P, begun in a previous paper, is completed. Several tables are given where the sub-algebras of dimension two to six are classified up to a conjugation and up to an isomorphism. In our method, a great use is made of tensor calculus, whose main results are recalled or stated in the beginning of the paper.     

Andreev reflection at the edge of a two-dimensional electron system with strong spin-orbit coupling

We experimentally investigate transport properties of a single planar junction between the niobium superconductor and the edge of a two-dimensional electron system in a narrow In_0.75Ga_0.25As quantum well with strong Rashba-type spin-orbit coupling. We experimentally demonstrate suppression of Andreev reflection at low biases at ultralow temperatures. From the analysis of temperature and magnetic field behavior, we interpret the observed suppression as a result of a spin-orbit coupling. There is also an experimental sign of the topological superconductivity realization in the present structure.