40,859 research outputs found
d_{xy}-Density wave in fermion-fermion cold atom mixtures
We study density wave instabilities in a doubly-degenerate Fermi-Fermi
mixture with symmetry on a square lattice. For sufficiently
large on-site inter-species repulsion, when the two species of fermions are
both at half-filling, two conventional (-wave) number density waves are
formed with a -phase difference between them to minimize the inter-species
repulsion. Upon moving one species away from half-filling, an unconventional
density wave with -wave symmetry emerges. When both species are away
from the vicinity of half-filling, superconducting instabilities dominate. We
present results of a functional renormalization-group calculation that maps out
the phase diagram at weak couplings. Also, we provide a simple explanation for
the emergence of the -density wave phase based on a four-patch model.
We find a robust and general mechanism for -density-wave formation that
is related to the shape and size of the Fermi surfaces. The density imbalance
between the two species of fermions in the vicinity of half-filling leads to
phase-space discrepancy for different inter-species Umklapp couplings. Using a
phase space argument for leading corrections in the one-loop renormalization
group approach to fermions, we show that the phase-space discrepancy in our
system causes opposite flows for the two leading intra-species Umklapp
couplings and that this triggers the -density-wave instability.Comment: revised long version; 8 pages, 7 figure
Bose-Einstein condensation in an optical lattice
In this paper we develop an analytic expression for the critical temperature
for a gas of ideal bosons in a combined harmonic lattice potential, relevant to
current experiments using optical lattices. We give corrections to the critical
temperature arising from effective mass modifications of the low energy
spectrum, finite size effects and excited band states. We compute the critical
temperature using numerical methods and compare to our analytic result. We
study condensation in an optical lattice over a wide parameter regime and
demonstrate that the critical temperature can be increased or reduced relative
to the purely harmonic case by adjusting the harmonic trap frequency. We show
that a simple numerical procedure based on a piecewise analytic density of
states provides an accurate prediction for the critical temperature.Comment: 10 pages, 5 figure
Critical Entanglement for the Half-Filled Extended Hubbard Model
We study the ground state of the one-dimensional extended Hubbard model at
half-filling using the entanglement entropy calculated by Density Matrix
Renormalization Group (DMRG) techniques. We apply a novel curve fitting and
scaling method to accurately identify a order critical point as well
as a Berezinskii-Kosterlitz-Thouless (BKT) critical point. Using open boundary
conditions and medium-sized lattices with very small truncation errors, we are
able to achieve similar accuracy to previous authors. We also report
observations of finite-size and boundary effects that can be remedied with
careful pinning.Comment: 10 pages, 12 figure
EROSION AND THE LOSS OF SOIL PRODUCTIVITY ON THE TERRIL SOIL SERIES IN MINNESOTA
Land Economics/Use,
The Realization and Dectection of Weyl Semimetals and Chiral Anomaly in Cold Atomic Systems
In this work, we describe a method to realize 3D Weyl semimetal by coupling
multilayers of honeycomb optical lattice in the presence of a pair of Raman
lasers. The Raman lasers render each isolated honeycomb layer a Chern
insulator. With finite interlayer coupling, the bulk gap of the system closes
at certain out-of-plane momenta due to Raman assisted tunnelling and result in
the Weyl semimetal phase. Using experimentally relevant parameters, we show
that both one and two pairs of Weyl points can be realized by tuning the
interlayer coupling strength. We suggest that Landau-Zener tunnelling can be
used to detect Weyl points and show that the transition probability increases
dramatically when Weyl point emerges. The realization of chiral anomaly by
using a magnetic field gradient is also discussed.Comment: 6 pages, 5 figures. Comments are welcom
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