Magnetotransport in the presence of a longitudinal barrier: multiple quantum interference of edge states

Transport in a two-dimensional electron gas subject to an external magnetic field is analyzed in the presence of a \textit{longitudinal barrier.} We show that \textit{quantum interference of the edge states} bound by the longitudinal barrier results in a drastic change of the electron motion: the degenerate discrete Landau levels are transformed into an alternating sequence of energy bands and energy gaps. These features of the electron spectrum should result in a high sensitivity of thermodynamic and transport properties of the 2D electron gas to external fields. In particular, we predict giant oscillations of the ballistic conductance and discuss nonlinear current-voltage characteristics, coherent Bloch oscillations and effects of impuritiesComment: 4 pages, 3 figure

Magnetic breakdown induced Peierls transition

We predict the new type of phase transition in quasi one-dimensional system of interacting electrons at high magnetic fields, the stabilization of a density wave which transforms a two dimensional open Fermi surface into a periodic chain of large pockets with small distances between them. We show that quantum tunneling of electrons between the neighboring closed orbits enveloping these pockets transforms the electron spectrum into a set of extremely narrow energy bands and gaps that decreases the total electron energy, thus leading to a \emph{magnetic breakdown induced density wave} ground state analogous to the well-known instability of Peierls type.Comment: 4 pages, 4 figures; accepted for publication in Phys. Rev. Letter

Coulomb Ordering in Anderson-Localized Electron Systems

We consider an electron system under conditions of strong Anderson localization, taking into account interelectron long-range Coulomb repulsion. We have established that with the electron density going to zero the Coulomb interaction brings the arrangement of the Anderson localized electrons closer and closer to an ideal (Wigner) crystal lattice, provided the temperature is sufficiently low and the dimension of the system is > 1. The ordering occurs despite the fact that a random spread of the energy levels of the localized one-electron states, exceeding the mean Coulomb energy per electron, renders it impossible the electrons to be self-localized due to their mutual Coulomb repulsion This differs principally the Coulomb ordered Anderson localized electron system (COALES) from Wigner crystal, Wigner glass, and any other ordered electron or hole system that results from the Coulomb self-localization of electrons/holes. The residual disorder inherent to COALES is found to bring about a multi-valley ground-state degeneration akin to that in spin glass. With the electron density increasing, COALES is revealed to turn into Wigner glass or a glassy state of a Fermi-glass type depending on the width of the random spread of the electron levels.Comment: 4 pages, LaTeX 2.09, To appear in Phys.Rev B Rapid Communications, The abstract and the Introduction have been written anew to stress a principal difference between a new macroscopical state predicted in the paper and Wigner crystal or Wigner glass, some notations have been change

Non-Makovian decoherence of a two-level system weakly coupled to a bosonic bath

Bloch-Redfield equation is a common tool for studying evolution of qubit systems weakly coupled to environment. We investigate the accuracy of the Born approximation underlying this equation. We find that the high order terms in the perturbative expansion contain accumulating divergences that make straightforward Born approximation inappropriate. We develop diagrammatic technique to formulate, and solve the improved self-consistent Born approximation. This more accurate treatment reveals an exponential time dependent prefactor in the non-Markovian contribution dominating the qubit long-time relaxation found in Phys. Rev. B 71, 035318 (2005). At the same time, the associated dephasing is not affected and is described by the Born-Markov approximation.Comment: To appear in EuroPhys. Let

Giant oscillations of the current in a dirty 2D electron system flowing perpendicular to a lateral barrier under magnetic field

The charge transport in a dirty 2-dimensional electron system biased in the presence of a lateral potential barrier under magnetic field is theoretically studied. The quantum tunneling across the barrier provides the quantum interference of the edge states localized on its both sides that results in giant oscillations of the charge current flowing perpendicular to the lateral junction. Our theoretical analysis is in a good agreement with the experimental observations presented in Ref.8. In particular, positions of the conductance maxima coincide with the Landau levels while the conductance itself is essentially suppressed even at the energies at which the resonant tunneling occurs and hence these puzzling observations can be resolved without taking into account the electron-electron interaction.Comment: 6 pages, 4 figure

Wigner-like crystallization of Anderson-localized electron systems with low electron densities

We consider an electron system under conditions of strong Anderson localization, taking into account interelectron long-range Coulomb repulsion. We establish that at sufficiently low electron densities and sufficiently low temperatures the Coulomb electron interaction brings about ordering of the Anderson-localized electrons into a structure that is close to an ideal (Wigner) crystal lattice, provided the dimension of the system is >1. This Anderson-Wigner glass (AWG) is a new macroscopic electron state that, on the one hand, is beyond the conventional Fermi glass concept, and on the other hand, qualitatively differs from the known "plain" Wigner glass (inherent in self-localized electron systems) in that the random slight electron displacements from the ideal crystal sites depend essentially on the electron density. With increasing electron density the AWG is found to turn into the plain Wigner glass or Fermi glass, depending on the width of the random spread of the electron levels. It is shown that the residual disorder of the AWG is characterized by a multivalley ground-state degeneracy akin to that in a spin glass. Some general features of the AWG are discussed, and a new conduction mechanism of a creep type is predicted. (C) 2002 American Institute of Physics

The Ground State of the ``Frozen'' Electron Phase in Two-Dimensional Narrow-Band Conductors with a Long-Range Interelectron Repulsion. Stripe Formation and Effective Lowering of Dimension

In narrow-band conductors a weakly screened Coulomb interelectron repulsion can supress narrow-band electrons' hopping, resulting in formation of a ``frozen'' electron phase which differs principally from any known macroscopic self-localized electron state including the Wigner crystal. In a zero-bandwidth limit the ``frozen'' electron phase is a classical lattice system with a long-range interparticle repulsion. The ground state of such systems has been considered in the case of two dimensions for an isotropic pair potential of the mutual particle repulsion. It has been shown that particle ordering into stripes and effective lowering of dimension universally resides in the ground state for any physically reasonable pair potential and for any geometry of the conductor lattice. On the basis of this fact a rigorous general procedure to fully describe the ground state has been formulated. Arguments have been adduced that charge ordering in High-T_c superconductors testifies to presence of a ``frozen'' electron phase in these systems.Comment: 5 pages, LaTeX 2.09, 1 figure in external PostScript files. To appear in Phys.Rev B Rapid Communication

Damping of field-induced chemical potential oscillations in ideal two-band compensated metals

The field and temperature dependence of the de Haas-van Alphen oscillations spectrum is studied for an ideal two-dimensional compensated metal. It is shown that the chemical potential oscillations, involved in the frequency combinations observed in the case of uncompensated orbits, are strongly damped and can even be suppressed when the effective masses of the electron- and hole-type orbits are the same. When magnetic breakdown between bands occurs, this damping is even more pronounced and the Lifshits-Kosevich formalism accounts for the data in a wide field range.Comment: 11 pages, 10 figures, to appear in PR

Recent developments in the determination of the amplitude and phase of quantum oscillations for the linear chain of coupled orbits

De Haas-van Alphen oscillations are studied for Fermi surfaces (FS) illustrating the model proposed by Pippard in the early sixties, namely the linear chain of orbits coupled by magnetic breakdown. This FS topology is relevant for many multiband quasi-two dimensional (q-2D) organic metals such as $\kappa$-(BEDT-TTF)$_2$Cu(NCS)$_2$ and $\theta$-(BEDT-TTF)$_4$CoBr$_4$(C$_6$H$_4$Cl$_2$) which are considered in detail. Whereas the Lifshits-Kosevich model only involves a first order development of field- and temperature-dependent damping factors, second order terms may have significant contribution on the Fourier components amplitude for such q-2D systems at high magnetic field and low temperature. The strength of these second order terms depends on the relative value of the involved damping factors, which are in turns strongly dependent on parameters such as the magnetic breakdown field, effective masses and, most of all, effective Land\'{e} factors. In addition, the influence of field-dependent Onsager phase factors on the oscillation spectra is considered.Comment: arXiv admin note: text overlap with arXiv:1304.665