598 research outputs found
Dynamics of one-dimensional Bose liquids: Andreev-like reflection at Y-junctions and absence of the Aharonov-Bohm effect
We study one dimensional Bose liquids of interacting ultracold atoms in the
Y-shaped potential when each branch is filled with atoms. We find that the
excitation packet incident on a single Y-junction should experience a negative
density reflection analogous to the Andreev reflection at normal-superconductor
interfaces, although the present system does not contain fermions. In a ring
interferometer type configuration, we find that the transport is completely
insensitive to the (effective) flux contained in the ring, in contrast to the
Aharonov-Bohm effect of a single particle in the same geometry.Comment: 4 pages, 2 figures, final versio
Quantum phase transitions in three-leg spin tubes
We investigate the properties of a three-leg quantum spin tube using several
techniques such as the density matrix renormalization group method, strong
coupling approaches and the non linear sigma model. For integer spins S, the
model proves to exhibit a particularly rich phase diagram consisting of an
ensemble of 2S phase transitions. They can be accurately identified by the
behavior of a non local string order parameter associated to the breaking of a
hidden symmetry in the Hamiltonian. The nature of these transitions are further
elucidated within the different approaches. We carry a detailed DMRG analysis
in the specific cases S = 1. The numerical data confirm the existence of two
Haldane phases with broken hidden symmetry separated by a trivial singlet
state. The study of the gap and of the von Neumann entropy suggest a first
order phase transition but at the close proximity of a tricritical point
separating a gapless and a first order transition line in the phase diagram of
the quantum spin tube.Comment: 20 pages, 18 figure
Fractional statistics and duality: strong tunneling behavior of edge states of quantum Hall liquids in the Jain sequence
While the values for the fractional charge and fractional statistics coincide
for fractional Hall (FQH) states in the Laughlin sequence, they do not for more
general FQH states, such as those in the Jain sequence. This mismatch leads to
additional phase factors in the weak coupling expansion for tunneling between
edge states which alter the nature of the strong tunneling limit. We show here
how to construct a weak-strong coupling duality for generalized FQH states with
simple unreconstructed edges. The correct dualization of quasiparticles into
integer charged fermions is a consistency requirement for a theory of FQH edge
states with a simple edge. We show that this duality also applies for weakly
reconstructed edges.Comment: 4+epsilon page
Haldane Gap and Hidden Order in the S=2 Antiferromagnetic Quantum Spin Chain
We have investigated Haldane's conjecture for the S=2 isotropic
antiferromagnetic quantum spin chain with nearest-neighbor exchange J. Using a
density matrix renormalization group algorithm for chains up to L=350 spins, we
find in the thermodynamic limit a finite spin gap of Delta = 0.085(5)J and a
finite spin-spin correlation length xi = 49(1) lattice spacings. We establish
the ground state energy per bond to be E_0=-4.761248(1)J. We show that the
ground state has a hidden topological order that is revealed in a nonlocal
string correlation function. This means that the physics of the S=2 chain can
be captured by a valence-bond solid description. We also observe effective free
spin-1 states at the ends of an open S=2 chain.Comment: 6 pages, LaTeX 2.09, 3 PostScript figure
Coupled Heisenberg antiferromagnetic chains in an effective staggered field
We present a systematic study of coupled Heisenberg antiferromagnetic
chains in an effective staggered field. We investigate several effects of the
staggered field in the {\em higher} ({\em two or three}) {\em dimensional} spin
system analytically. In particular, in the case where the staggered field and
the inter-chain interaction compete with each other, we predict, using
mean-field theory, a characteristic phase transition. The spin-wave theory
predicts that the behavior of the gaps induced by the staggered field is
different between the competitive case and the non-competitive case. When the
inter-chain interactions are sufficiently weak, we can improve the mean-field
phase diagram by using chain mean-field theory and the analytical results of
field theories. The ordered phase region predicted by the chain mean-field
theory is substantially smaller than that by the mean-field theory.Comment: 13pages, 12figures, to be published in PR
Symmetry protection of topological order in one-dimensional quantum spin systems
We discuss the characterization and stability of the Haldane phase in integer
spin chains on the basis of simple, physical arguments. We find that an odd-
Haldane phase is a topologically non-trivial phase which is protected by any
one of the following three global symmetries: (i) the dihedral group of
-rotations about and axes; (ii) time-reversal symmetry
; (iii) link inversion symmetry (reflection
about a bond center), consistently with previous results [Phys. Rev. B
\textbf{81}, 064439 (2010)]. On the other hand, an even- Haldane phase is
not topologically protected (i.e., it is indistinct from a trivial,
site-factorizable phase). We show some numerical evidence that supports these
claims, using concrete examples.Comment: 9 pages, 6 figures, extended version: several new examples and
numerical results added. Journal reference adde
Universal temperature dependence of the magnetization of gapped spin chains
Temperature dependence of the magnetization of the Haldane spin chain at
finite magnetic field is analyzed systematically. Quantum Monte Carlo data
indicates a clear minimum of magnetization as a function of temperature in the
gapless regime. On the basis of the Tomonaga-Luttinger liquid theory, we argue
that this minimum is rather universal and can be observed for general axially
symmetric quasi-one-dimensional spin systems. Our argument is confirmed by the
magnetic-field dependence of the spin-wave velocity obtained numerically. One
can estimate a magnitude of the gap of any such systems by fitting the
experimental data with the magnetization minimum.Comment: 9 pages, 7 figure
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