45 research outputs found
Symmetry Breaking on the Three-Dimensional Hyperkagome Lattice of Na_4Ir_3O_8
We study the antiferromagnetic spin-1/2 Heisenberg model on the highly
frustrated, three-dimensional, hyperkagome lattice of Na_4Ir_3O_8 using a
series expansion method. We propose a valence bond crystal with a 72 site unit
cell as a ground state that supports many, very low lying, singlet excitations.
Low energy spinons and triplons are confined to emergent lower-dimensional
motifs. Here, and for analogous kagome and pyrochlore states, we suggest finite
temperature signatures, including an Ising transition, in the magnetic specific
heat due to a multistep breaking of discrete symmetries.Comment: 4 pages, 3 figure
Frustrated three-leg spin tubes: from spin 1/2 with chirality to spin 3/2
Motivated by the recent discovery of the spin tube
[(CuCltachH)Cl]Cl, we investigate the properties of a frustrated
three-leg spin tube with antiferromagnetic intra-ring and inter-ring couplings.
We pay special attention to the evolution of the properties from weak to strong
inter-ring coupling and show on the basis of extensive density matrix
renormalization group and exact diagonalization calculations that the system
undergoes a first-order phase transition between a dimerized gapped phase at
weak coupling that can be described by the usual spin-chirality model and a
gapless critical phase at strong coupling that can be described by an effective
spin-3/2 model. We also show that there is a magnetization plateau at 1/3 in
the gapped phase and slightly beyond. The implications for
[(CuCltachH)Cl]Cl are discussed, with the conclusion that this
system behaves essentially as a spin-3/2 chain.Comment: 8 pages, 9 figures, revised versio
Competition between two- and three-sublattice ordering for S=1 spins on the square lattice
We provide strong evidence that the S=1 bilinear-biquadratic Heisenberg model
with nearest-neighbor interactions on the square lattice possesses an extended
three-sublattice phase induced by quantum fluctuations for sufficiently large
biquadratic interactions, in spite of the bipartite nature of the lattice. The
argumentation relies on exact diagonalizations of finite clusters and on a
semiclassical treatment of quantum fluctuations within linear flavor-wave
theory. In zero field, this three-sublattice phase is purely quadrupolar, and
upon increasing the field it replaces most of the plateau at 1/2 that is
predicted by the classical theory.Comment: 5 pages, 6 figures, minor changes, references adde
Quantum Many-Body Dynamics of Coupled Double-Well Superlattices
We propose a method for controllable generation of non-local entangled pairs
using spinor atoms loaded in an optical superlattice. Our scheme iteratively
increases the distance between entangled atoms by controlling the coupling
between the double wells. When implemented in a finite linear chain of 2N
atoms, it creates a triplet valence bond state with large persistency of
entanglement (of the order of N). We also study the non-equilibrium dynamics of
the one-dimensional ferromagnetic Heisenberg Hamiltonian and show that the time
evolution of a state of decoupled triplets on each double well leads to the
formation of a highly entangled state where short-distance antiferromagnetic
correlations coexist with longer-distance ferromagnetic ones. We present
methods for detection and characterization of the various dynamically generated
states. These ideas are a step forward towards the use of atoms trapped by
light as quantum information processors and quantum simulators.Comment: 13 pages, 10 figures, references adde
Quantum Quenches in Integrable Field Theories
We study the non equilibrium time evolution of an integrable field theory in
1+1 dimensions after a sudden variation of a global parameter of the
Hamiltonian. For a class of quenches defined in the text, we compute the long
times limit of the one point function of a local operator as a series of form
factors. Even if some subtleties force us to handle this result with care,
there is a strong evidence that for long times the expectation value of any
local operator can be described by a generalized Gibbs ensemble with a
different effective temperature for each eigenmode
The ALPS project: open source software for strongly correlated systems
We present the ALPS (Algorithms and Libraries for Physics Simulations)
project, an international open source software project to develop libraries and
application programs for the simulation of strongly correlated quantum lattice
models such as quantum magnets, lattice bosons, and strongly correlated fermion
systems. Development is centered on common XML and binary data formats, on
libraries to simplify and speed up code development, and on full-featured
simulation programs. The programs enable non-experts to start carrying out
numerical simulations by providing basic implementations of the important
algorithms for quantum lattice models: classical and quantum Monte Carlo (QMC)
using non-local updates, extended ensemble simulations, exact and full
diagonalization (ED), as well as the density matrix renormalization group
(DMRG). The software is available from our web server at
http://alps.comp-phys.org.Comment: For full software and introductory turorials see
http://alps.comp-phys.or
Entanglement entropy of integer Quantum Hall states in polygonal domains
The entanglement entropy of the integer Quantum Hall states satisfies the
area law for smooth domains with a vanishing topological term. In this paper we
consider polygonal domains for which the area law acquires a constant term that
only depends on the angles of the vertices and we give a general expression for
it. We study also the dependence of the entanglement spectrum on the geometry
and give it a simple physical interpretation.Comment: 8 pages, 6 figure
Fate of Quasiparticle at Mott Transition and Interplay with Lifshitz Transition Studied by Correlator Projection Method
Filling-control metal-insulator transition on the two-dimensional Hubbard
model is investigated by using the correlator projection method, which takes
into account momentum dependence of the free energy beyond the dynamical
mean-field theory. The phase diagram of metals and Mott insulators is analyzed.
Lifshitz transitions occur simultaneously with metal-insulator transitions at
large Coulomb repulsion. On the other hand, they are separated each other for
lower Coulomb repulsion, where the phase sandwiched by the Lifshitz and
metal-insulator transitions appears to show violation of the Luttinger sum
rule. Through the metal-insulator transition, quasiparticles retain nonzero
renormalization factor and finite quasi-particle weight in the both sides of
the transition. This supports that the metal-insulator transition is caused not
by the vanishing renormalization factor but by the relative shift of the Fermi
level into the Mott gap away from the quasiparticle band, in sharp contrast
with the original dynamical mean-field theory. Charge compressibility diverges
at the critical end point of the first-order Lifshitz transition at finite
temperatures. The origin of the divergence is ascribed to singular momentum
dependence of the quasiparticle dispersion.Comment: 24 pages including 10 figure
Can we always get the entanglement entropy from the Kadanoff-Baym equations? The case of the T-matrix approximation
We study the time-dependent transmission of entanglement entropy through an
out-of-equilibrium model interacting device in a quantum transport set-up. The
dynamics is performed via the Kadanoff-Baym equations within many-body
perturbation theory. The double occupancy , needed to determine the entanglement entropy, is obtained from
the equations of motion of the single-particle Green's function. A remarkable
result of our calculations is that can become negative, thus not permitting to evaluate the
entanglement entropy. This is a shortcoming of approximate, and yet conserving,
many-body self-energies. Among the tested perturbation schemes, the -matrix
approximation stands out for two reasons: it compares well to exact results in
the low density regime and it always provides a non-negative . For the second part of this statement, we
give an analytical proof. Finally, the transmission of entanglement across the
device is diminished by interactions but can be amplified by a current flowing
through the system.Comment: 6 pages, 6 figure