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ABSTRACT: We present Quantum Monte-Carlo simulations of an exchange-anisotropic
spin-1/2 Heisenberg model on a square lattice with nearest and next-nearest
neighbor interactions. The ground state phase diagram shows two classical
magnetically ordered phases for dominating antiferromagnetic S^z-interactions
and for large quantum fluctuations a ferromagnetic order in the x-y plane. In
between a finite region is detected where neither classical nor quantum
mechanical order, e.g. long-ranged dimer correlations, are found.
Journal of Physics Conference Series 01/2012; 391:012156.
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ABSTRACT: We investigate the phase diagram of hard-core bosons on a square lattice with
competing interactions. The hard-core bosons can be represented also by
spin-1/2 operators and the model can therefore be mapped onto an anisotropic
$J_1$-$J_2$-Heisenberg model. We find the N\'eel state and a collinear
antiferromagnetic state as classical ordered phases to be suppressed for small
ferromagnetic exchange terms $J_{1,2}^{x,y}$ and a ferromagnetic phase which
orders in the x-y-plane for large $J_{1,2}^{x,y}$. For an intermediate regime
the emergence of new quantum states like valence bond crystals or super-solids
is predicted for similar models. We do not observe any signal for long-range
order in terms of conventional order or dimer correlations in our model and
find an exponential decay in the spin correlations. Hence, all evidence is
pointing towards a quantum disordered ground state for a small region in the
phase diagram.
Physical Review B 05/2011; 83(17):174519. · 3.69 Impact Factor
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B. Bauer,
L. D. Carr,
H. G. Evertz,
A. Feiguin,
J. Freire, S. Fuchs,
L. Gamper,
J. Gukelberger,
E. Gull,
S. Guertler, [......],
V. W. Scarola,
U. Schollwöck,
C Silva,
B. Surer,
S Todo,
S. Trebst,
M. Troyer,
M. L. Wall,
P Werner,
S. Wessel
[show abstract]
[hide abstract]
ABSTRACT: We present release 2.0 of the ALPS (Algorithms and Libraries for Physics
Simulations) project, an 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. The code development is centered on common XML and HDF5 data formats,
libraries to simplify and speed up code development, common evaluation and
plotting tools, and simulation programs. The programs enable non-experts to
start carrying out serial or parallel 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), the density matrix
renormalization group (DMRG) both in a static version and a dynamic
time-evolving block decimation (TEBD) code, and quantum Monte Carlo solvers for
dynamical mean field theory (DMFT). The ALPS libraries provide a powerful
framework for programers to develop their own applications, which, for
instance, greatly simplify the steps of porting a serial code onto a parallel,
distributed memory machine. Major changes in release 2.0 include the use of
HDF5 for binary data, evaluation tools in Python, support for the Windows
operating system, the use of CMake as build system and binary installation
packages for Mac OS X and Windows, and integration with the VisTrails workflow
provenance tool. The software is available from our web server at
http://alps.comp-phys.org/.
01/2011;
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ABSTRACT: We study the thermodynamic properties of the 3D Hubbard model for
temperatures down to the Neel temperature using cluster dynamical mean-field
theory. In particular we calculate the energy, entropy, density, double
occupancy and nearest-neighbor spin correlations as a function of chemical
potential, temperature and repulsion strength. To make contact with cold-gas
experiments, we also compute properties of the system subject to an external
trap in the local density approximation. We find that an entropy per particle
$S/N \approx 0.65(6)$ at $U/t=8$ is sufficient to achieve a Neel state in the
center of the trap, substantially higher than the entropy required in a
homogeneous system. Precursors to antiferromagnetism can clearly be observed in
nearest-neighbor spin correlators.
09/2010;
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[hide abstract]
ABSTRACT: We present an algorithm for the analytic continuation of imaginary-time quantum Monte Carlo data. The algorithm is strictly based on principles of Bayesian statistical inference. It utilizes Monte Carlo simulations to calculate a weighted average of possible energy spectra. We apply the algorithm to imaginary-time quantum Monte Carlo data and compare the resulting energy spectra with those from a standard maximum entropy calculation.
Journal of Physics Conference Series 02/2010; 200(1):012041.
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[show abstract]
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ABSTRACT: We use improved Monte-Carlo algorithms to study the antiferromagnetic 2D-Ising model with competing interactions $J_1$ on nearest neighbour and $J_2$ on next-nearest neighbour bonds. The finite-temperature phase diagram is divided by a critical point at $J_2 = J_1/2$ where the groundstate is highly degenerate. To analyse the phase boundaries we look at the specific heat and the energy distribution for various ratios of $J_2/J_1$. We find a first order transition for small $J_2 > J_1/2$ and the transition temperature suppressed to $T_C=0$ at the critical point.
Journal of Physics Conference Series 01/2009; 145(1):012051.
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[show abstract]
[hide abstract]
ABSTRACT: We restudy the phase diagram of the 2D-Ising model with competing interactions $J_1$ on nearest neighbour and $J_2$ on next-nearest neighbour bonds via Monte-Carlo simulations. We present the finite temperature phase diagram and introduce computational methods which allow us to calculate transition temperatures close to the critical point at $J_2 = 0.5 J_1$. Further on we investigate the character of the different phase boundaries and find that the transition is weakly first order for moderate $J_2 > 0.5 J_1$.
Physics of Condensed Matter 10/2008; 65(4):533-537. · 1.53 Impact Factor
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A.F. Albuquerque,
F. Alet,
P. Corboz,
P. Dayal,
A. Feiguin, S. Fuchs,
L. Gamper,
E. Gull,
S. Gürtler,
A. Honecker, [......],
R.M. Noack,
G. Pawłowski,
L. Pollet,
T. Pruschke,
U. Schollwöck,
S. Todo,
S. Trebst,
M. Troyer,
P. Werner,
S. Wessel
[show abstract]
[hide abstract]
ABSTRACT: We present release 1.3 of 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). Changes in the new release include a DMRG program for interacting models, support for translation symmetries in the diagonalization programs, the ability to define custom measurement operators, and support for inhomogeneous systems, such as lattice models with traps. The software is available from our web server at http://alps.comp-phys.org/.
Journal of Magnetism and Magnetic Materials 03/2007; 310(2):1187-1193. · 1.78 Impact Factor
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A. F. Albuquerque,
F. Alet,
P. Corboz,
P. Dayal,
A. Feiguin, S. Fuchs,
L. Gamper,
E. Gull,
S. Guertler,
A. Honecker, [......],
R. M. Noack,
G. Pawlowski,
L. Pollet,
T. Pruschke,
U. Schollwock,
S Todo,
S. Trebst,
M. Troyer,
P Werner,
S. Wessel
[show abstract]
[hide abstract]
ABSTRACT: We present release 1.3 of 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). Changes in the new release include a DMRG program for interacting models, support for translation symmetries in the diagonalization programs, the ability to define custom measurement operators, and support for inhomogeneous systems, such as lattice models with traps. The software is available from our web server at http://alps.comp-phys.org/ .
Journal of Magnetism and Magnetic Materials 03/2007; 310(2):1187–1193. · 1.78 Impact Factor
