1,508 research outputs found
Low-energy excitations in the magnetized state of the bond-alternating quantum S=1 chain system NTENP
High intensity inelastic neutron scattering experiments on the S=1
quasi-one-dimensional bond-alternating antiferromagnet Ni(C9D24N4)(NO2)ClO4
(NTENP) are performed in magnetic fields of up to 14.8~T. Excitation in the
high field magnetized quantum spin solid (ordered) phase are investigated. In
addition to the previously observed coherent long-lived gap excitation [M.
Hagiwara et al., Phys. Rev. Lett 94, 177202 (2005)], a broad continuum is
detected at lower energies. This observation is consistent with recent
numerical studies, and helps explain the suppression of the lowest-energy gap
mode in the magnetized state of NTENP. Yet another new feature of the
excitation spectrum is found at slightly higher energies, and appears to be
some kind of multi-magnon state.Comment: 5 pages, 4 fugure
Analysis of a SU(4) generalization of Halperin's wave function as an approach towards a SU(4) fractional quantum Hall effect in graphene sheets
Inspired by the four-fold spin-valley symmetry of relativistic electrons in
graphene, we investigate a possible SU(4) fractional quantum Hall effect, which
may also arise in bilayer semiconductor quantum Hall systems with small Zeeman
gap. SU(4) generalizations of Halperin's wave functions [Helv. Phys. Acta 56,
75 (1983)], which may break differently the original SU(4) symmetry, are
studied analytically and compared, at nu=2/3, to exact-diagonalization studies.Comment: 4+epsilon pages, 4 figures; published version with minor correction
Characterizing the many-body localization transition through the entanglement spectrum
We numerically explore the many body localization (MBL) transition through
the lens of the {\it entanglement spectrum}. While a direct transition from
localization to thermalization is believed to obtain in the thermodynamic limit
(the exact details of which remain an open problem), in finite system sizes
there exists an intermediate `quantum critical' regime. Previous numerical
investigations have explored the crossover from thermalization to criticality,
and have used this to place a numerical {\it lower} bound on the critical
disorder strength for MBL. A careful analysis of the {\it high energy} part of
the entanglement spectrum (which contains universal information about the
critical point) allows us to make the first ever observation in exact numerics
of the crossover from criticality to MBL and hence to place a numerical {\it
upper bound} on the critical disorder strength for MBL.Comment: 4 pages+appendi
Haldane Statistics in the Finite Size Entanglement Spectra of Laughlin States
We conjecture that the counting of the levels in the orbital entanglement
spectra (OES) of finite-sized Laughlin Fractional Quantum Hall (FQH) droplets
at filling is described by the Haldane statistics of particles in a
box of finite size. This principle explains the observed deviations of the OES
counting from the edge-mode conformal field theory counting and directly
provides us with a topological number of the FQH states inaccessible in the
thermodynamic limit- the boson compactification radius. It also suggests that
the entanglement gap in the Coulomb spectrum in the conformal limit protects a
universal quantity- the statistics of the state. We support our conjecture with
ample numerical checks.Comment: 4.1 pages, published versio
Numerical investigation of gapped edge states in fractional quantum Hall-superconductor heterostructures
Fractional quantum Hall-superconductor heterostructures may provide a
platform towards non-abelian topological modes beyond Majoranas. However their
quantitative theoretical study remains extremely challenging. We propose and
implement a numerical setup for studying edge states of fractional quantum Hall
droplets with a superconducting instability. The fully gapped edges carry a
topological degree of freedom that can encode quantum information protected
against local perturbations. We simulate such a system numerically using exact
diagonalization by restricting the calculation to the quasihole-subspace of a
(time-reversal symmetric) bilayer fractional quantum Hall system of Laughlin
states. We show that the edge ground states are permuted by
spin-dependent flux insertion and demonstrate their fractional Josephson
effect, evidencing their topological nature and the Cooper pairing of
fractionalized quasiparticles.Comment: 12 pages, 9 figure
Atypical Fractional Quantum Hall Effect in Graphene at Filling Factor 1/3
We study the recently observed graphene fractional quantum Hall state at a
filling factor using a four-component trial wave function and exact
diagonalization calculations. Although it is adiabatically connected to a 1/3
Laughlin state in the upper spin branch, with SU(2) valley-isospin
ferromagnetic ordering and a completely filled lower spin branch, it reveals
physical properties beyond such a state that is the natural ground state for a
large Zeeman effect. Most saliently, it possesses at experimentally relevant
values of the Zeeman gap low-energy spin-flip excitations that may be unveiled
in inelastic light-scattering experiments.Comment: 4 pages, 3 figures; slightly modified published versio
Bulk-Edge Correspondence in the Entanglement Spectra
Li and Haldane conjectured and numerically substantiated that the
entanglement spectrum of the reduced density matrix of ground-states of
time-reversal breaking topological phases (fractional quantum Hall states)
contains information about the counting of their edge modes when the
ground-state is cut in two spatially distinct regions and one of the regions is
traced out. We analytically substantiate this conjecture for a series of FQH
states defined as unique zero modes of pseudopotential Hamiltonians by finding
a one to one map between the thermodynamic limit counting of two different
entanglement spectra: the particle entanglement spectrum, whose counting of
eigenvalues for each good quantum number is identical (up to accidental
degeneracies) to the counting of bulk quasiholes, and the orbital entanglement
spectrum (the Li-Haldane spectrum). As the particle entanglement spectrum is
related to bulk quasihole physics and the orbital entanglement spectrum is
related to edge physics, our map can be thought of as a mathematically sound
microscopic description of bulk-edge correspondence in entanglement spectra. By
using a set of clustering operators which have their origin in conformal field
theory (CFT) operator expansions, we show that the counting of the orbital
entanglement spectrum eigenvalues in the thermodynamic limit must be identical
to the counting of quasiholes in the bulk. The latter equals the counting of
edge modes at a hard-wall boundary placed on the sample. Moreover, we show this
to be true even for CFT states which are likely bulk gapless, such as the
Gaffnian wavefunction.Comment: 20 pages, 6 figure
Bridge between Abelian and Non-Abelian Fractional Quantum Hall States
We propose a scheme to construct the most prominent Abelian and non-Abelian
fractional quantum Hall states from K-component Halperin wave functions. In
order to account for a one-component quantum Hall system, these SU(K) colors
are distributed over all particles by an appropriate symmetrization. Numerical
calculations corroborate the picture that the proposed scheme allows for a
unification of both Abelian and non-Abelian trial wave functions in the study
of one-component quantum Hall systems.Comment: 4 pages, 2 figures; revised version, published in Phys. Rev. Let
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