21,829 research outputs found
Haldane Sashes in Quantum Hall Spectra
We show that the low-temperature sash features in the lowest Landau-level
(LLL) tunneling density-of-states (TDOS) recently discovered by Dial and
Ashoori are intimately related to the discrete Haldane-pseudopotential
interaction energy scales that govern fractional quantum Hall physics. Our
analysis is based on expressions for the tunneling density-of-states which
become exact at filling factors close to and , where the sash
structure is most prominent. We comment on other aspects of LLL correlation
physics that can be revealed by accurate temperature-dependent tunneling data.Comment: Added referenc
Asymptotically exact trial wave functions for yrast states of rotating Bose gases
We revisit the composite fermion (CF) construction of the lowest angular
momentum yrast states of rotating Bose gases with weak short range interaction.
For angular momenta at and below the single vortex, , the overlaps
between these trial wave functions and the corresponding exact solutions {\it
increase} with increasing system size and appear to approach unity in the
thermodynamic limit. In the special case , this remarkable behaviour was
previously observed numerically. Here we present methods to address this point
analytically, and find strongly suggestive evidence in favour of similar
behaviour for all . While not constituting a fully conclusive proof
of the converging overlaps, our results do demonstrate a striking similarity
between the analytic structure of the exact ground state wave functions at , and that of their CF counterparts. Results are given for two different
projection methods commonly used in the CF approach
Edge State Tunneling in a Split Hall Bar Model
In this paper we introduce and study the correlation functions of a chiral
one-dimensional electron model intended to qualitatively represent narrow Hall
bars separated into left and right sections by a penetrable barrier. The model
has two parameters representing respectively interactions between top and
bottom edges of the Hall bar and interactions between the edges on opposite
sides of the barrier. We show that the scaling dimensions of tunneling
processes depend on the relative strengths of the interactions, with repulsive
interactions across the Hall bar tending to make breaks in the barrier
irrelevant. The model can be solved analytically and is characterized by a
difference between the dynamics of even and odd Fourier components. We address
its experimental relevance by comparing its predictions with those of a more
geometrically realistic model that must be solved numerically.Comment: 13 pages, including 4 figures,final version as publishe
Angular Momentum Distribution Function of the Laughlin Droplet
We have evaluated the angular-momentum distribution functions for finite
numbers of electrons in Laughlin states. For very small numbers of electrons
the angular-momentum state occupation numbers have been evaluated exactly while
for larger numbers of electrons they have been obtained from Monte-Carlo
estimates of the one-particle density matrix. An exact relationship, valid for
any number of electrons, has been derived for the ratio of the occupation
numbers of the two outermost orbitals of the Laughlin droplet and is used to
test the accuracy of the MC calculations. We compare the occupation numbers
near the outer edges of the droplets with predictions based on the chiral
Luttinger liquid picture of Laughlin state edges and discuss the surprisingly
large oscillations in occupation numbers which occur for angular momenta far
from the edge.Comment: 11 pages of RevTeX, 2 figures available on request. IUCM93-00
Numerical Tests of the Chiral Luttinger Liquid Theory for Fractional Hall Edges
We report on microscopic numerical studies which support the chiral Luttinger
liquid theory of the fractional Hall edge proposed by Wen. Our calculations are
based in part on newly proposed and accurate many-body trial wavefunctions for
the low-energy edge excitations of fractional incompressible states.Comment: 12 pages + 1 figure, Revte
Interaction-Enhanced Coherence Between Two-Dimensional Dirac Layers
We estimate the strength of interaction-enhanced coherence between two
graphene or topological insulator surface-state layers by solving
imaginary-axis gap equations in the random phase approximation. Using a
self-consistent treatment of dynamic screening of Coulomb interactions in the
gapped phase, we show that the excitonic gap can reach values on the order of
the Fermi energy at strong interactions. The gap is discontinuous as a function
of interlayer separation and effective fine structure constant, revealing a
first order phase transition between effectively incoherent and interlayer
coherent phases. To achieve the regime of strong coherence the interlayer
separation must be smaller than the Fermi wavelength, and the extrinsic
screening of the medium embedding the Dirac layers must be negligible. In the
case of a graphene double-layer we comment on the supportive role of the remote
-bands neglected in the two-band Dirac model.Comment: 14 pages, 9 figure
Collective excitations in double-layer quantum Hall systems
We study the collective excitation spectra of double-layer quantum-Hall
systems using the single mode approximation. The double-layer in-phase density
excitations are similar to those of a single-layer system. For out-of-phase
density excitations, however, both inter-Landau-level and intra-Landau-level
double-layer modes have finite dipole oscillator strengths. The oscillator
strengths at long wavelengths for the latter transitions are shifted upward by
interactions by identical amounts proportional to the interlayer Coulomb
coupling. The intra-Landau-level out-of-phase mode has a gap when the ground
state is incompressible except in the presence of spontaneous inter-layer
coherence. We compare our results with predictions based on the
Chern-Simons-Landau-Ginzburg theory for double-layer quantum Hall systems.Comment: RevTeX, 21 page
Valley-Hall Kink and Edge States in Multilayer Graphene
We report on a theoretical study of one-dimensional (1D) states localized at
few-layer graphene system ribbon edges, and at interfaces between few-layer
graphene systems with different valley Hall conductivities. These 1D states are
topologically protected when valley mixing is neglected. We address the
influence on their properties of stacking arrangement, interface structure, and
external electric field perpendicular to the layers. We find that 1D states are
generally absent at multilayer ribbon armchair direction edges, but present
irrespective of crystallographic orientation at any internal valley-Hall
interface of an ABC stacked multilayer.Comment: 5 pages, 3 figure
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