14 research outputs found
Uniform and staggered magnetizations induced by Dzyaloshinskii-Moriya interactions in isolated and coupled spin 1/2 dimers in a magnetic field
We investigate the interplay of Dzyaloshinskii-Moriya interactions and an
external field in spin 1/2 dimers. For isolated dimers and at low field, we
derive simple expressions for the staggered and uniform magnetizations which
show that the orientation of the uniform magnetization can deviate
significantly from that of the external field. In fact, in the limit where the
vector of the Dzyaloshinskii-Moriya interaction is parallel to the
external field, the uniform magnetization actually becomes {\it perpendicular}
to the field. For larger fields, we show that the staggered magnetization of an
isolated dimer has a maximum close to one-half the polarization, with a large
maximal value of in the limit of very small Dzyaloshinskii-Moriya
interaction. We investigate the effect of inter-dimer coupling in the context
of ladders with Density Matrix Renormalization Group (DMRG) calculations and
show that, as long as the values of the Dzyaloshinskii-Moriya and of the
exchange interaction are compatible with respect to the development of a
staggered magnetization, the simple picture that emerges for isolated dimers is
also valid for weakly coupled dimers with minor modifications. The results are
compared with torque measurements on
Cu(CHN)Cl.Comment: 8 pages, 9 figure
Topological invariants and interacting one-dimensional fermionic systems
We study one-dimensional, interacting, gapped fermionic systems described by
variants of the Peierls-Hubbard model and characterize their phases via a
topological invariant constructed out of their Green's functions. We
demonstrate that the existence of topologically protected, zero-energy states
at the boundaries of these systems can be tied to the values of their
topological invariant, just like when working with the conventional,
noninteracting topological insulators. We use a combination of analytical
methods and the numerical density matrix renormalization group method to
calculate the values of the topological invariant throughout the phase diagrams
of these systems, thus deducing when topologically protected boundary states
are present. We are also able to study topological states in spin systems
because, deep in the Mott insulating regime, these fermionic systems reduce to
spin chains. In this way, we associate the zero-energy states at the end of an
antiferromagnetic spin-one Heisenberg chain with the topological invariant 2.Comment: 15 pages, 11 figures, Final Version as published in PR
Time evolution of Matrix Product States
In this work we develop several new simulation algorithms for 1D many-body
quantum mechanical systems combining the Matrix Product State variational
ansatz with Taylor, Pade and Arnoldi approximations to the evolution operator.
By comparing all methods with previous techniques based on Trotter
decompositions we demonstrate that the Arnoldi method is the best one, reaching
extremely good accuracy with moderate resources. Finally we apply this
algorithm to studying the formation of molecules in an optical lattices when
crossing a Feschbach resonance with a cloud of two-species hard-core bosons.Comment: More extensive comparison with all nearest-neighbor spin s=1/2
models. The results in this manuscript have been superseded by a more
complete work in cond-mat/061021
Coherent matter waves emerging from Mott-insulators
We study the formation of (quasi-)coherent matter waves emerging from a Mott
insulator for strongly interacting bosons on a one-dimensional lattice. It has
been shown previously that a quasi-condensate emerges at momentum k=\pi/2a,
where a is the lattice constant, in the limit of infinitely strong repulsion
(hard-core bosons). Here we show that this phenomenon persists for all values
of the repulsive interaction that lead to a Mott insulator at a commensurate
filling. The non-equilibrium dynamics of hard-core bosons is treated exactly by
means of a Jordan-Wigner transformation, and the generic case is studied using
a time-dependent density matrix renormalization group technique. Different
methods for controlling the emerging matter wave are discussed.Comment: 20 pages, 11 figures. Published versio
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
Tracking spin and charge with spectroscopy in spin-polarised 1D systems
We calculate the spectral function of a one-dimensional strongly interacting
chain of fermions, where the response can be well understood in terms of spinon
and holon excitations. Upon increasing the spin imbalance between the spin
species, we observe the single-electron response of the fully polarised system
to emanate from the holon peak while the spinon response vanishes. For
experimental setups that probe one-dimensional properties, we propose this
method as an additional generic tool to aid the identification of spectral
structures, e.g. in ARPES measurements. We show that this applies even to
trapped systems having cold atomic gas experiments in mind.Comment: 5 pages, 4 figure
Dynamical Transition in the Open-boundary Totally Asymmetric Exclusion Process
We revisit the totally asymmetric simple exclusion process with open
boundaries (TASEP), focussing on the recent discovery by de Gier and Essler
that the model has a dynamical transition along a nontrivial line in the phase
diagram. This line coincides neither with any change in the steady-state
properties of the TASEP, nor the corresponding line predicted by domain wall
theory. We provide numerical evidence that the TASEP indeed has a dynamical
transition along the de Gier-Essler line, finding that the most convincing
evidence was obtained from Density Matrix Renormalisation Group (DMRG)
calculations. By contrast, we find that the dynamical transition is rather hard
to see in direct Monte Carlo simulations of the TASEP. We furthermore discuss
in general terms scenarios that admit a distinction between static and dynamic
phase behaviour.Comment: 27 pages, 18 figures. v2 to appear in J Phys A features minor
corrections and better-quality figure