19 research outputs found
Conductance of a Mott Quantum Wire
We consider transport through a one-dimensional conductor subject to an
external periodic potential and connected to non-interacting leads (a "Mott
quantum wire"). For the case of a strong periodic potential, the conductance is
shown to jump from zero, for the chemical potential lying within the
Mott-Hubbard gap, to the non-interacting value of 2e^2/h, as soon as the
chemical potential crosses the gap edge. This behavior is strikingly different
from that of an optical conductivity, which varies continuously with the
carrier concentration. For the case of a weak potential, the perturbative
correction to the conductance due to Umklapp scattering is absent away from
half-filling.Comment: 4 pages, RevTex, 1 ps figure included; published versio
Quasi-Andreev reflection in inhomogeneous Luttinger liquids
Reflection of charge excitations at the step in the interaction strength in a
Luttinger liquid can be of the Andreev type, even if the interactions are
purely repulsive. The region with stronger repulsion plays the role of a normal
metal in a normal-metal /superconductor junction, whereas the region with
weaker repulsion plays the role of a superconductor. It is shown that this
quasi-Andreev reflection leads to a number of proximity-like effects, including
the local enhancement (suppression) of superconducting fluctuations on the
quasi-normal (quasi-superconducting) side of the step, significant modification
of the local density of states, as well as others. The observable consequences
of these proximity effects are analyzed for the case of single- and
two-particle tunneling from a normal-metal or superconducting tip into an
inhomogeneous Luttinger-liquid wire.Comment: 5 pages, 2 figures (eps
Neuronavigation in the Percutaneous Treatment of Trigeminal Neuralgia: Technical note
Objective: To describe neuronavigation-guided percutaneous radiofrequency thermocoagulation in the treatment of trigeminal neuralgia.Methods: Neuronavigation guided percutaneous radiofrequency thermocoagulation of the Gasser ganglion was used in nine patients with trigeminal neuralgia who developed resistance to drugs used in the treatment of TN or have had adverse effects due to drug toxicity. The age of the patients was between 62 and 78 years. Results: All patients had immediate pain relief after thermocoagulation guided by neuronavigation. Neuronavigation allowed visualization of instrument position in relation to target and the related anatomical structures. The technique helped preoperative planning of the optimal trajectory for needle insertion. There were no complications of the procedure.Conclusion: Image guided percutaneous thermocoagulation in the treatment of trigeminal neuralgia is a safe and promising procedure. The technique has reduced the risk of postoperative complications caused by “hunting” of the foramen ovale. 
Anomalous Thermal Transport in Quantum Wires
We study thermal transport in a one-dimensional quantum wire, connected to
reservoirs. Despite of the absence of electron backscattering, interactions in
the wire strongly influence thermal transport. Electrons propagate with unitary
transmission through the wire and electric conductance is not affected. Energy,
however, is carried by bosonic excitations (plasmons) which suffer from
scattering even on scales much larger than the Fermi wavelength. If the
electron density varies randomly, plasmons are localized and {\em charge-energy
separation} occurs. We also discuss the effect of plasmon-plasmon interaction
using Levinson's theory of nonlocal heat transport.Comment: replaced with published versio
Short--range impurity in the vicinity of a saddle point and the levitation of the 2D delocalized states in a magnetic field
The effect of a short--range impurity on the transmission through a
saddle--point potential for an electron, moving in a strong magnetic field, is
studied. It is demonstrated that for a random position of an impurity and
random sign of its potential the impurity--induced mixing of the Landau levels
diminishes {\em on average} the transmission coefficient. This results in an
upward shift (levitation) of the energy position of the delocalized state in a
smooth potential. The magnitude of the shift is estimated. It increases with
decreasing magnetic field as .Comment: LaTeX, 20 page
Topological Phase Diagram of a Two-Subband Electron System
We present a phase diagram for a two-dimensional electron system with two
populated subbands. Using a gated GaAs/AlGaAs single quantum well, we have
mapped out the phases of various quantum Hall states in the density-magnetic
filed plane. The experimental phase diagram shows a very different topology
from the conventional Landau fan diagram. We find regions of negative
differential Hall resistance which are interpreted as preliminary evidence of
the long sought reentrant quantum Hall transitions. We discuss the origins of
the anomalous topology and the negative differential Hall resistance in terms
of the Landau level and subband mixing.Comment: 4 pages, 4 figure
Quantifying the levitation picture of extended states in lattice models
The behavior of extended states is quantitatively analyzed for two
dimensional lattice models. A levitation picture is established for both
white-noise and correlated disorder potentials. In a continuum limit window of
the lattice models we find simple quantitative expressions for the extended
states levitation, suggesting an underlying universal behavior. On the other
hand, these results point out that the Quantum Hall phase diagrams may be
disorder dependent.Comment: 5 pages, submitted to PR
Levitation of quantum Hall critical states in a lattice model with spatially correlated disorder
The fate of the current carrying states of a quantum Hall system is
considered in the situation when the disorder strength is increased and the
transition from the quantum Hall liquid to the Hall insulator takes place. We
investigate a two-dimensional lattice model with spatially correlated disorder
potentials and calculate the density of states and the localization length
either by using a recursive Green function method or by direct diagonalization
in connection with the procedure of level statistics. From the knowledge of the
energy and disorder dependence of the localization length and the density of
states (DOS) of the corresponding Landau bands, the movement of the current
carrying states in the disorder--energy and disorder--filling-factor plane can
be traced by tuning the disorder strength.
We show results for all sub-bands, particularly the traces of the Chern and
anti-Chern states as well as the peak positions of the DOS. For small disorder
strength we recover the well known weak levitation of the critical states,
but we also reveal, for larger , the strong levitation of these states
across the Landau gaps without merging. We find the behavior to be similar for
exponentially, Gaussian, and Lorentzian correlated disorder potentials. Our
study resolves the discrepancies of previously published work in demonstrating
the conflicting results to be only special cases of a general lattice model
with spatially correlated disorder potentials.
To test whether the mixing between consecutive Landau bands is the origin of
the observed floating, we truncate the Hilbert space of our model Hamiltonian
and calculate the behavior of the current carrying states under these
restricted conditions.Comment: 10 pages, incl. 13 figures, accepted for publication in PR
Quantum Hall - insulator transitions in lattice models with strong disorder
We report results of numerical studies of the integer quantum Hall effect in
a tight binding model on a two-dimensional square lattice with non-interacting
electrons, in the presence of a random potential as well as a uniform magnetic
field applied perpendicular to the lattice. We consider field magnitudes such
that the area per flux quantum is commensurate with the lattice structure.
Topological properties of the single electron wave functions are used to
identify current carrying states that are responsible for the quantized Hall
conductance. We study the interplay between the magnetic field and the
disorder, and find a universal pattern with which the current carrying states
are destroyed by increasing disorder strength, and the system driven into an
insulating state. We also discuss how to interpolate results of lattice models
to the continuum limit. The relationship to previous theoretical and
experimental studies of quantum Hall-insulator transitions in strongly
disordered systems at low magnetic fields is discussed.Comment: 20 pages, 6 figure