40 research outputs found
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
-(BEDT-TTF)Cu(NCS) and
-(BEDT-TTF)CoBr(CHCl) 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