2,151 research outputs found
Exact Pseudofermion Action for Monte Carlo Simulation of Domain-Wall Fermion
We present an exact pseudofermion action for hybrid Monte Carlo simulation
(HMC) of one-flavor domain-wall fermion (DWF), with the effective 4-dimensional
Dirac operator equal to the optimal rational approximation of the overlap-Dirac
operator with kernel , where and are constants. Using this exact pseudofermion action, we perform HMC of
one-flavor QCD, and compare its characteristics with the widely used rational
hybrid Monte Carlo algorithm (RHMC). Moreover, to demonstrate the practicality
of the exact one-flavor algorithm (EOFA), we perform the first dynamical
simulation of the (1+1)-flavors QCD with DWF.Comment: 13 pages, 4 figures, v2: Simulation of (1+1)-flavors QCD with DWF,
and references added. To appear in Phys. Lett.
Unquenched QCD with Light Quarks
We present recent results in unquenched lattice QCD with two degenerate light
sea quarks using the truncated determinant approximation (TDA). In the TDA the
infrared modes contributing to the quark determinant are computed exactly up to
some cutoff in quark off-shellness (typically 2). This approach
allows simulations to be performed at much lighter quark masses than possible
with conventional hybrid MonteCarlo techniques. Results for the static energy
and topological charge distributions are presented using a large ensemble
generated on very coarse (6) but physically large lattices. Preliminary
results are also reported for the static energy and meson spectrum on 10x20
lattices (lattice scale =1.15 GeV) at quark masses corresponding to
pions of mass 200 MeV. Using multiboson simulation to compute the
ultraviolet part of the quark determinant the TDA approach becomes an exact
with essentially no increase in computational effort. Some preliminary results
using this fully unquenched algorithm are presented.Comment: LateX, 39 pages, 16 eps figures, 1 ps figur
Status and challenges of simulations with dynamical fermions
An overview over the current state of algorithms for dynamical fermion
simulations is given. In particular some insight into the functioning of the
determinant spitting techniques is discussed. The critical slowing down of the
simulations towards the continuum limit and the role of the boundary conditions
is also reviewed.Comment: 20 pages, 9 figures, plenary talk presented at the 30th International
Symposium on Lattice Field Theory - Lattice 2012, June 24-29, 2012 Cairns,
Australi
Chiral Skyrmionic matter in non-centrosymmetric magnets
Axisymmetric magnetic strings with a fixed sense of rotation and nanometer
sizes (chiral magnetic vortices or Skyrmions) have been predicted to exist in a
large group of non-centrosymmetric crystals more than two decades ago. Recently
these extraordinary magnetic states have been directly observed in thin layers
of cubic helimagnet (Fe,Co)Si. In this report we apply our earlier theoretical
findings to review main properties of chiral Skyrmions, to elucidate their
physical nature, and to analyse these recent experimental results on
magnetic-field-driven evolution of Skyrmions and helicoids in chiral
helimagnets.Comment: 13 pages, 7 figures, invited talk - JEMS-2010 ( 23-28 August, Krakow,
Poland
Robust zero-energy modes in an electronic higher-order topological insulator: the dimerized Kagome lattice
Quantum simulators are an essential tool for understanding complex quantum
materials. Platforms based on ultracold atoms in optical lattices and photonic
devices led the field so far, but electronic quantum simulators are proving to
be equally relevant. Simulating topological states of matter is one of the holy
grails in the field. Here, we experimentally realize a higher-order electronic
topological insulator (HOTI). Specifically, we create a dimerized Kagome
lattice by manipulating carbon-monoxide (CO) molecules on a Cu(111) surface
using a scanning tunneling microscope (STM). We engineer alternating weak and
strong bonds to show that a topological state emerges at the corner of the
non-trivial configuration, while it is absent in the trivial one. Contrarily to
conventional topological insulators (TIs), the topological state has two
dimensions less than the bulk, denoting a HOTI. The corner mode is protected by
a generalized chiral symmetry, which leads to a particular robustness against
perturbations. Our versatile approach to quantum simulation with artificial
lattices holds promises of revealing unexpected quantum phases of matter
Featureless and non-fractionalized Mott insulators on the honeycomb lattice at 1/2 site filling
Within the Landau paradigm, phases of matter are distinguished by spontaneous
symmetry breaking. Implicit here is the assumption that a completely symmetric
state exists: a paramagnet. At zero temperature such quantum featureless
insulators may be forbidden, triggering either conventional order or
topological order with fractionalized excitations. Such is the case for
interacting particles when the particle number per unit cell, f, is not an
integer. But, can lattice symmetries forbid featureless insulators even at
integer f? An especially relevant case is the honeycomb (graphene) lattice ---
where free spinless fermions at f=1 (the two sites per unit cell mean f=1 is
half filling per site) are always metallic. Here we present wave functions for
bosons, and a related spin-singlet wave function for spinful electrons, on the
f=1 honeycomb, and demonstrate via quantum to classical mappings that they do
form featureless Mott insulators. The construction generalizes to symmorphic
lattices at integer f in any dimension. Our results explicitly demonstrate that
in this case, despite the absence of a non-interacting insulator at the same
filling, lack of order at zero temperature does not imply fractionalization.Comment: v2: major revision including new result on SU(2) spinful electron
state and additional author. v3: PNAS published version. 7 pages, 5 figures;
appendix 5 pages, 3 figure
Physics issues in simulations with dynamical overlap fermions
We discuss the impact of various improvements on simulations of dynamical
overlap fermions using the Hybrid Monte Carlo algorithm. We focus on the usage
of fat links and multiple pseudo-fermion fields.Comment: 14 pages, 10 figure
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