271 research outputs found
Comment on ``One-Dimensional Disordered Bosonic Hubbard Model: A Density-Matrix Renormalization Group Study"
We present the phase diagram of the system obtained by continuous-time
worldline Monte Carlo simulations, and demonstrate that the actual phase
diagram is in sharp contrast with that found in Phys. Rev. Lett., 76 (1996)
2937.Comment: 1 page, LaTex, 1 figur
Phase diagram of anisotropic boson t-J model
We have studied by Quantum Monte Carlo simulations the low temperature phase
diagram of a mixture of isotopic, hard core bosons, described by the t-Jz-Jperp
model, with Jperp=a Jz. Coexistence of superfluid hole-rich and insulating,
antiferromagnetically ordered hole-free phases is observed at sufficiently low
hole density, for any a < 1. A two-component checkerboard supersolid phase is
not observed. The experimental relevance and possible broader implications of
these findings are discussed.Comment: Replaced with published versio
Low-Temperature Quantum Relaxation in a System of Magnetic Nanomolecules
We argue that to explain recent resonant tunneling experiments on crystals of
Mn and Fe, particularly in the low-T limit, one must invoke dynamic
nuclear spin and dipolar interactions. We show the low-, short-time
relaxation will then have a form, where depends on the
nuclear , on the tunneling matrix element between the two
lowest levels, and on the initial distribution of internal fields in the
sample, which depends very strongly on sample shape. The results are directly
applicable to the system. We also give some results for the long-time
relaxation.Comment: 4 pages, 3 PostScript figures, LaTe
Radiative transfer in ultra-relativistic outflows
Analytical and numerical solutions are obtained for the equation of radiative
transfer in ultra-relativistic opaque jets. The solution describes the initial
trapping of radiation, its adiabatic cooling, and the transition to
transparency. Two opposite regimes are examined: (1) Matter-dominated outflow.
Surprisingly, radiation develops enormous anisotropy in the fluid frame before
decoupling from the fluid. The radiation is strongly polarized. (2)
Radiation-dominated outflow. The transfer occurs as if radiation propagated in
vacuum, preserving the angular distribution and the blackbody shape of the
spectrum. The escaping radiation has a blackbody spectrum if (and only if) the
outflow energy is dominated by radiation up to the photospheric radius.Comment: 12 pages, 8 figures, accepted to Ap
Continuous-Time Quantum Monte Carlo Algorithm for the Lattice Polaron
An efficient continuous-time path-integral Quantum Monte Carlo algorithm for
the lattice polaron is presented. It is based on Feynman's integration of
phonons and subsequent simulation of the resulting single-particle
self-interacting system. The method is free from the finite-size and
finite-time-step errors and works in any dimensionality and for any range of
electron-phonon interaction. The ground-state energy and effective mass of the
polaron are calculated for several models. The polaron spectrum can be measured
directly by Monte Carlo, which is of general interest.Comment: 5 pages, 4 figures, published versio
Resonant Inelastic X-Ray Scattering in Metals: A Diagrammatic Approach
We develop a formalism to study the Resonant Inelastic X-ray Scattering
(RIXS) response in metals based on the diagrammatic expansion for its cross
section. The standard approach to the solution of the RIXS problem relies on
two key approximations: short-range potentials and non-interacting conduction
electrons. However, these approximations are inaccurate for charged particles
in metals, where the long-range Coulomb interaction and dynamic screening
effects are very important. In this work we study how to extract important
information about collective excitations in the Coulomb plasma, plasmons and
electron-hole pairs, from RIXS data. We find that single- and multi-plasmon
excitations can easily be distinguished by positions of the corresponding
peaks, singularities, and their intensities. We also discuss the hybrid
processes, where plasmon emission is accompanied by excitation of electron-hole
pairs, and study how they manifest themselves.Comment: 5 pages, 5 figures, Appendi
Diagrammatic Monte Carlo for Correlated Fermions
We show that Monte Carlo sampling of the Feynman diagrammatic series (DiagMC)
can be used for tackling hard fermionic quantum many-body problems in the
thermodynamic limit by presenting accurate results for the repulsive Hubbard
model in the correlated Fermi liquid regime. Sampling Feynman's diagrammatic
series for the single-particle self-energy we can study moderate values of the
on-site repulsion () and temperatures down to . We
compare our results with high temperature series expansion and with single-site
and cluster dynamical mean-field theory.Comment: 4 pages, 5 figures, stylistic change
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