204 research outputs found
The Hofstadter Energy Spectrum for an Interacting 2DEG
We study the effects of the Coulomb interactions between electrons on the
Hofstadter butterfly, which characterizes the subband structure of the Landau
levels of a two-dimensional electron gas in a perpendicular homogeneous
magnetic field and a periodic lateral superlattice potential. The interactions
essentially preserve the intricate gap structure of the Hofstadter spectra, but
with a lower symmetry that depends on the filling of the Landau bands. For
short enough periods and strong enough modulation the miniband structure can be
resolved in the thermodynamic density of states.Comment: LaTeX 4 pages with 3 PostScript figures, Contribution to EP2DSXI
Nottingham August 95 to appear in Surface Scienc
Regarding the editorial by Sau and Ng. 'Hypertrophic cardiomyopathy risk stratification based on clinical or dynamic electrophysiological features: two sides of the same coin'
This Letter to the Editor refers to article ‘Hypertrophic cardiomyopathy risk stratification based on clinical or dynamic electrophysiological features: two sides of the same coin’ by Sau A, Ng, FS https://doi.org/10.1093/europace/euad072. ‘Response to the letter to the editor EUPC-D-23-00362 of Richard Saumarez’, by Arunashis Sau and Fu Siong Ng, https://doi.org/10.1093/europace/euad174
Phase--coherence Effects in Antidot Lattices: A Semiclassical Approach to Bulk Conductivity
We derive semiclassical expressions for the Kubo conductivity tensor. Within
our approach the oscillatory parts of the diagonal and Hall conductivity are
given as sums over contributions from classical periodic orbits in close
relation to Gutzwiller's trace formula for the density of states. Taking into
account the effects of weak disorder and temperature we reproduce recently
observed anomalous phase coherence oscillations in the conductivity of large
antidot arrays.Comment: 11 pages, 2 figures available under request, RevTe
Manifestation of the Hofstadter butterfly in far-infrared absorption
The far-infrared absorption of a two-dimensional electron gas with a
square-lattice modulation in a perpendicular constant magnetic field is
calculated self-consistently within the Hartree approximation. For strong
modulation and short period we obtain intra- and intersubband magnetoplasmon
modes reflecting the subbands of the Hofstadter butterfly in two or more Landau
bands. The character of the absorption and the correlation of the peaks to the
number of flux quanta through each unit cell of the periodic potential depends
strongly on the location of the chemical potential with respect to the
subbands, or what is the same, on the density of electrons in the system.Comment: RevTeX file + 4 postscript figures, to be published Phys. Rev. B
Rapid Com
Duality Relation among Periodic Potential Problems in the Lowest Landau Level
Using a momentum representation of a magnetic von Neumann lattice, we study a
two-dimensional electron in a uniform magnetic field and obtain one-particle
spectra of various periodic short-range potential problems in the lowest Landau
level.We find that the energy spectra satisfy a duality relation between a
period of the potential and a magnetic length. The energy spectra consist of
the Hofstadter-type bands and flat bands. We also study the connection between
a periodic short-range potential problem and a tight-binding model.Comment: 6 pages, 3 figures, final version to appear in PR
Magnetization in short-period mesoscopic electron systems
We calculate the magnetization of the two-dimensional electron gas in a
short-period lateral superlattice, with the Coulomb interaction included in
Hartree and Hartree-Fock approximations. We compare the results for a finite,
mesoscopic system modulated by a periodic potential, with the results for the
infinite periodic system. In addition to the expected strong exchange effects,
the size of the system, the type and the strength of the lateral modulation
leave their fingerprints on the magnetization.Comment: RevTeX4, 10 pages with 14 included postscript figures To be published
in PRB. Replaced to repair figure
Bloch Electrons in a Magnetic Field - Why Does Chaos Send Electrons the Hard Way?
We find that a 2D periodic potential with different modulation amplitudes in
x- and y-direction and a perpendicular magnetic field may lead to a transition
to electron transport along the direction of stronger modulation and to
localization in the direction of weaker modulation. In the experimentally
accessible regime we relate this new quantum transport phenomenon to avoided
band crossing due to classical chaos.Comment: 4 pages, 3 figures, minor modifications, PRL to appea
Hall conductance of Bloch electrons in a magnetic field
We study the energy spectrum and the quantized Hall conductance of electrons
in a two-dimensional periodic potential with perpendicular magnetic field
WITHOUT neglecting the coupling of the Landau bands. Remarkably, even for weak
Landau band coupling significant changes in the Hall conductance compared to
the one-band approximation of Hofstadter's butterfly are found. The principal
deviations are the rearrangement of subbands and unexpected subband
contributions to the Hall conductance.Comment: to appear in PRB; Revtex, 9 pages, 5 postscript figures; figures with
better resolution may be obtained from http://www.chaos.gwdg.d
Signature of Chaotic Diffusion in Band Spectra
We investigate the two-point correlations in the band spectra of spatially
periodic systems that exhibit chaotic diffusion in the classical limit. By
including level pairs pertaining to non-identical quasimomenta, we define form
factors with the winding number as a spatial argument. For times smaller than
the Heisenberg time, they are related to the full space-time dependence of the
classical diffusion propagator. They approach constant asymptotes via a regime,
reflecting quantal ballistic motion, where they decay by a factor proportional
to the number of unit cells. We derive a universal scaling function for the
long-time behaviour. Our results are substantiated by a numerical study of the
kicked rotor on a torus and a quasi-one-dimensional billiard chain.Comment: 8 pages, REVTeX, 5 figures (eps
Should lethal arrhythmias in hypertrophic cardiomyopathy be predicted using non-electrophysiological methods?
While sudden cardiac death (SCD) in hypertrophic cardiomyopathy (HCM) is due to arrhythmias, the guidelines for prediction of SCD are based solely on non-electrophysiological methods. This study aims to stimulate thinking about whether the interests of patients with HCM are better served by using current, 'risk factor', methods of prediction or by further development of electrophysiological methods to determine arrhythmic risk. Five published predictive studies of SCD in HCM, which contain sufficient data to permit analysis, were analysed to compute receiver operating characteristics together with their confidence bounds to compare their formal prediction either by bootstrapping or Monte Carlo analysis. Four are based on clinical risk factors, one with additional MRI analysis, and were regarded as exemplars of the risk factor approach. The other used an electrophysiological method and directly compared this method to risk factors in the same patients. Prediction methods that use conventional clinical risk factors and MRI have low predictive capacities that will only detect 50-60% of patients at risk with a 15-30% false positive rate [area under the curve (AUC) = ∼0.7], while the electrophysiological method detects 90% of events with a 20% false positive rate (AUC = ∼0.89). Given improved understanding of complex arrhythmogenesis, arrhythmic SCD is likely to be more accurately predictable using electrophysiologically based approaches as opposed to current guidelines and should drive further development of electrophysiologically based methods
- …