111 research outputs found
Magnetization process from Chern-Simons theory and its application to SrCu(BO)
URL: http://www-spht.cea.fr/articles/T02/081 16th Nishinomiya-Yukawa Memorial Symposium, Nishinomiya, Japan, November 2001 http://fr.arxiv.org/abs/cond-mat/0204161In two-dimensional systems, it is possible transmute bosons into fermions by use of a Chern-Simons gauge field. Such a mapping is used to compute magnetization processes of two-dimensional magnets. The calculation of the magnetization curve then involves the structure of the Hofstadter problem for the lattice under consideration. Certain features of the Hofstadter butterfly are shown to imply the appearance of magnetization plateaus. While not always successfull, this approach leads to interesting results when applied to the 2D AF magnet \SrCu
Disorder and interactions in quantum Hall ferromagnets: effects of disorder in Skyrmion physics
We present a Hartree-Fock study of the competition between disorder and
interactions in quantum Hall ferromagnets near . We find that the ground
state at evolves with increasing interaction strength from a
quasi-metallic paramagnet, to a partially spin-polarized ferromagnetic Anderson
insulator, and to a fully spin-polarized ferromagnet with a charge gap. Away
from , the ground state evolves from a conventional Anderson insulator,
to a conventional quasiparticle glass, and finally to a ferromagnetic Skyrmion
quasiparticle glass. These different regimes can be measured in low-temperature
transport and NMR experiments. We present calculations for the NMR spectra in
different disorder regimes.Comment: 3 pages, 3 figures, proceedings for EP2DS-14, Prague 200
Exotic Quantum Order in Low-Dimensional Systems
Strongly correlated quantum systems in low dimensions often exhibit novel
quantum ordering. This ordering is sometimes hidden and can be revealed only by
examining new `dual' types of correlations. Such ordering leads to novel
collective modes and fractional quantum numbers. Examples will be presented
from quantum spin chains and the quantum Hall effect.Comment: To appear in Solid State Communications, Proceedings of Symposium on
the Advancing Frontiers in Condensed Matter Science. 12pages +6 PS figure
Properties of the Soliton-Lattice State in Double-Layer Quantum Hall Systems
Application of a sufficiently strong parallel magnetic field produces a soliton-lattice (SL) ground state in a double-layer quantum
Hall system. We calculate the ground-state properties of the SL state as a
function of for total filling factor , and obtain the
total energy, anisotropic SL stiffness, Kosterlitz-Thouless melting
temperature, and SL magnetization. The SL magnetization might be experimentally
measurable, and the magnetic susceptibility diverges as .Comment: 4 pages LaTeX, 1 EPS figure. Proceedings of the 12th International
Conference on the Electronic Properties of Two-Dimensional Electron Systems
(EP2DS-12), to be published in Physica B (1998
Formation of an Edge Striped Phase in Fractional Quantum Hall Systems
We have performed an exact diagonalization study of up to N=12 interacting
electrons on a disk at filling for both Coulomb and
short-range interaction for which Laughlin wave function is the exact solution.
For Coulomb interaction and we find persistent radial oscillations
in electron density, which are not captured by the Laughlin wave function. Our
results srongly suggest formation of a chiral edge striped phase in quantum
Hall systems. The amplitude of the charge density oscillations decays slowly,
perhaps as a square root of the distance from the edge; thus the spectrum of
edge excitations is likely to be affected.Comment: 4 pages, 3 Figs. include
Soluble `Supersymmetric' Quantum XY Model
We present a `supersymmetric' modification of the -dimensional quantum
rotor model whose ground state is exactly soluble. The model undergoes a
vortex-binding transition from insulator to metal as the rotor coupling is
varied. The Hamiltonian contains three-site terms which are relevant: they
change the universality class of the transition from that of the ()--- to
the -dimensional classical XY model. The metallic phase has algebraic ODLRO
but the superfluid density is identically zero. Variational wave functions for
single-particle and collective excitations are presented.Comment: 12 pages, REVTEX 3.0, IUCM93-00
A Quantum Hall Fluid of Vortices
In this note we demonstrate that vortices in a non-relativistic Chern-Simons
theory form a quantum Hall fluid. We show that the vortex dynamics is
controlled by the matrix mechanics previously proposed by Polychronakos as a
description of the quantum Hall droplet. As the number of vortices becomes
large, they fill the plane and a hydrodynamic treatment becomes possible,
resulting in the non-commutative theory of Susskind. Key to the story is the
recent D-brane realisation of vortices and their moduli spaces.Comment: 10 pages. v2(3): (More) References adde
Phase transition and spin-wave dispersion in quantum Hall bilayers at filling factor nu=1
We present an effective Hamiltonian for a bilayer quantum Hall system at
filling factor neglecting charge fluctuations. Our model is formulated
in terms of spin and pseudospin operators and is an exact representation of the
system within the above approximation. We analyze its low-lying excitations in
terms of spin-wave theory. Moreover we add to previous first-principle
exact-diagonalization studies concentrating on the quantum phase transition
seen in this system.Comment: Four pages, proceedings for EP2DS-14, Prague 200
Liouvillian Approach to the Integer Quantum Hall Effect Transition
We present a novel approach to the localization-delocalization transition in
the integer quantum Hall effect. The Hamiltonian projected onto the lowest
Landau level can be written in terms of the projected density operators alone.
This and the closed set of commutation relations between the projected
densities leads to simple equations for the time evolution of the density
operators. These equations can be used to map the problem of calculating the
disorder averaged and energetically unconstrained density-density correlation
function to the problem of calculating the one-particle density of states of a
dynamical system with a novel action. At the self-consistent mean-field level,
this approach yields normal diffusion and a finite longitudinal conductivity.
While we have not been able to go beyond the saddle point approximation
analytically, we show numerically that the critical localization exponent can
be extracted from the energetically integrated correlation function yielding
in excellent agreement with previous finite-size scaling
studies.Comment: 9 pages, submitted to PR
Magnetoroton instabilities and static susceptibilities in higher Landau levels
We present analytical results concerning the magneto-roton instability in
higher Landau levels evaluated in the single mode approximation. The roton gap
appears at a finite wave vector, which is approximately independent of the LL
index n, in agreement with numerical calculations in the composite-fermion
picture. However, a large maximum in the static susceptibility indicates a
charge density modulation with wave vectors , as
expected from Hartree-Fock predictions. We thus obtain a unified description of
the leading charge instabilities in all LLs.Comment: 4 pages, 5 figure
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