1,683 research outputs found
Influence of trigonal warping on interference effects in bilayer graphene
Bilayer graphene (two coupled graphitic monolayers arranged according to Bernal stacking) is a two-dimensional gapless semiconductor with a peculiar electronic spectrum different from the Dirac spectrum in the monolayer material. In particular, the electronic Fermi line in each of its valleys has a strong p -> -p asymmetry due to trigonal warping, which suppresses the weak localization effect. We show that weak localization in bilayer graphene may be present only in devices with pronounced intervalley scattering, and we evaluate the corresponding magnetoresistance
Anderson-Hubbard model with box disorder: Statistical dynamical mean-field theory investigation
Strongly correlated electrons with box disorder in high-dimensional lattices
are investigated. We apply the statistical dynamical mean-field theory, which
treats local correlations non-perturbatively. The incorporation of a finite
lattice connectivity allows for the detection of disorder-induced localization
via the probability distribution function of the local density of states. We
obtain a complete paramagnetic ground state phase diagram and find
correlation-induced as well as disorder-induced metal-insulator transitions.
Our results qualitatively confirm predictions obtained by typical medium
theory. Moreover, we find that the probability distribution function of the
local density of states in the metallic phase strongly deviates from a
log-normal distribution as found for the non-interacting case.Comment: 13 pages, 15 figures, published versio
Many-Impurity Effects in Fourier Transform Scanning Tunneling Spectroscopy
Fourier transform scanning tunneling spectroscopy (FTSTS) is a useful
technique for extracting details of the momentum-resolved electronic band
structure from inhomogeneities in the local density of states due to
disorder-related quasiparticle scattering. To a large extent, current
understanding of FTSTS is based on models of Friedel oscillations near isolated
impurities. Here, a framework for understanding many-impurity effects is
developed based on a systematic treatment of the variance Delta rho^2(q,omega)
of the Fourier transformed local density of states rho(q,\omega). One important
consequence of this work is a demonstration that the poor signal-to-noise ratio
inherent in rho(q,omega) due to randomness in impurity positions can be
eliminated by configuration averaging Delta rho^2(q,omega). Furthermore, we
develop a diagrammatic perturbation theory for Delta rho^2(q,omega) and show
that an important bulk quantity, the mean-free-path, can be extracted from
FTSTS experiments.Comment: 7 pages, 5 figures. A version of the paper with high resolution,
colour figures is available at
http://www.trentu.ca/physics/batkinson/FTSTS.ps.gz minor revisions in
response to refree report + figure 5 is modifie
Absence of weak antilocalization in ferromagnetic films
We present magnetoresistance measurements performed on ultrathin films of
amorphous Ni and Fe. In these films the Curie temperature drops to zero at
small thickness, making it possible to study the effect of ferromagnetism on
localization. We find that non-ferromagnetic films are characterized by
positive magnetoresistance. This is interpreted as resulting from weak
antilocalization due to strong Bychkov-Rashba spin orbit scattering. As the
films become ferromagnetic the magnetoresistance changes sign and becomes
negative. We analyze our data to identify the individual contributions of weak
localization, weak antilocalization and anisotropic magnetoresistance and
conclude that the magnetic order suppresses the influence of spin-orbit effects
on localization phenomena in agreement with theoretical predictions.Comment: 6 pages, 6 figure
Critical level statistics and anomalously localized states at the Anderson transition
We study the level-spacing distribution function at the Anderson
transition by paying attention to anomalously localized states (ALS) which
contribute to statistical properties at the critical point. It is found that
the distribution for level pairs of ALS coincides with that for pairs of
typical multifractal states. This implies that ALS do not affect the shape of
the critical level-spacing distribution function. We also show that the
insensitivity of to ALS is a consequence of multifractality in tail
structures of ALS.Comment: 8 pages, 5 figure
Weak-localization corrections to the conductivity of double quantum wells
The weak-localization contribution \delta\sigma(B) to the conductivity of a
tunnel-coupled double-layer electron system is evaluated and its behavior in
weak magnetic fields B perpendicular or parallel to the layers is examined. In
a perpendicular field B, \delta \sigma(B) increases and remains dependent on
tunneling as long as the magnetic field is smaller than \hbar/e D \tau_t, where
D is the in-plane diffusion coefficient and \tau_t the interlayer tunneling
time. If \tau_t is smaller than the inelastic scattering time, a parallel
magnetic field also leads to a considerable increase of the concuctivity
starting with a B**2 law and saturating at fields higher than \hbar/e Z (D
\tau_t)**(1/2), where Z is the interlayer distance. In the limit of coherent
tunneling, when \tau_t is comparable to elastic scattering time, \delta
\sigma(B) differs from that of a single-layer system due to ensuing
modifications of the diffusion coefficient. A possibility to probe the
weak-localization effect in double-layer systems by the dependence of the
conductivity on the gate-controlled level splitting is discussed.Comment: Text 18 pages in Latex/Revtex format, 4 Postscript figures. J. Phys.:
CM,in pres
Conductance fluctuations in a quantum dot under almost periodic ac pumping
It is shown that the variance of the linear dc conductance fluctuations in an
open quantum dot under a high-frequency ac pumping depends significantly on the
spectral content of the ac field. For a sufficiently strong ac field
, where is the dephasing rate induced by
ac noise and is the electron escape rate, the dc conductance
fluctuations are much stronger for the harmonic pumping than in the case of the
noise ac field of the same intensity. The reduction factor in a static
magnetic field takes the universal value of 2 only for the white--noise
pumping. For the strictly harmonic pumping of
sufficiently large intensity the variance is almost insensitive to the static
magnetic field . For the quasi-periodic ac
field of the form with
and we predict the novel
effect of enchancement of conductance fluctuations at commensurate frequencies
.Comment: 4 pages RevTex, 4 eps figures; the final version to appear in
Phys.Rev.
Long-Range Spatial Correlations of Eigenfunctions in Quantum Disordered Systems
This paper is devoted to the statistics of the quantum eigenfunctions in an
ensemble of finite disordered systems (metallic grains). We focus on moments of
inverse participation ratio. In the universal random matrix limit that
corresponds to the infinite conductance of the grains, these moments are
self-averaging quantities. At large but finite conductance the moments do
fluctuate due to the long range correlations in the eigenfunctions. We evaluate
the distributions of fluctuations at given conductance and geometry of the
grains and express them through the spectrum of the diffusion operator in the
grain.Comment: RevTeX, 4 pages, no figur
Localization of correlated fermions in optical lattices with speckle disorder
Strongly correlated fermions in three- and two-dimensional optical lattices
with experimentally realistic speckle disorder are investigated. We extend and
apply the statistical dynamical mean-field theory, which treats local
correlations non-perturbatively, to incorporate on-site and hopping-type
randomness on equal footing. Localization due to disorder is detected via the
probability distribution function of the local density of states. We obtain a
complete paramagnetic ground state phase diagram for experimentally realistic
parameters and find a strong suppression of the correlation-induced metal
insulator transition due to disorder. Our results indicate that the
Anderson-Mott and the Mott insulator are not continuously connected due to the
specific character of speckle disorder. Furthermore, we discuss the effect of
finite temperature on the single-particle spectral function.Comment: 12 pages, 16 figures, published versio
Magnetic-field-dependent zero-bias diffusive anomaly in Pb oxide-n-InAs structures: Coexistence of two- and three-dimensional states
The results of experimental and theoretical studies of zero-bias anomaly
(ZBA) in the Pb-oxide-n-InAs tunnel structures in magnetic field up to 6T are
presented. A specific feature of the structures is a coexistence of the 2D and
3D states at the Fermi energy near the semiconductor surface. The dependence of
the measured ZBA amplitude on the strength and orientation of the applied
magnetic field is in agreement with the proposed theoretical model. According
to this model, electrons tunnel into 2D states, and move diffusively in the 2D
layer, whereas the main contribution to the screening comes from 3D electrons.Comment: 8 double-column pages, REVTeX, 9 eps figures embedded with epsf,
published versio
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