9,421 research outputs found
Fulde-Ferrell--Larkin-Ovchinnikov state in the dimensional crossover between one- and three-dimensional lattices
We present a full phase diagram for the one-dimensional (1D) to
three-dimensional (3D) crossover of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)
state in an attractive Hubbard model of 3D-coupled chains in a har- monic trap.
We employ real-space dynamical mean-field theory which describes full local
quantum fluctuations beyond the usual mean-field and local density
approximation. We find strong dimensionality effects on the shell structure
undergoing a crossover between distinctive quasi-1D and quasi-3D regimes. We
predict an optimal regime for the FFLO state that is considerably extended to
intermediate interchain couplings and polarizations, directly realizable with
ultracold atomic gases. We find that the 1D-like FFLO feature is vulnerable to
thermal fluctuations, while the FFLO state of mixed 1D-3D character can be
stabilized at a higher temperature
Slowest and Fastest Information Scrambling in the Strongly Disordered XXZ Model
We present a perturbation method to compute the out-of-time-ordered
correlator in the strongly disordered Heisenberg XXZ model in the deep
many-body localized regime. We characterize the discrete structure of the
information propagation across the eigenstates, revealing a highly structured
light cone confined by the strictly logarithmic upper and lower bounds
representing the slowest and fastest scrambling available in this system. We
explain these bounds by deriving the closed-form expression of the effective
interaction for the slowest scrambling and by constructing the effective model
of a half-length for the fastest scrambling. We extend our lowest-order
perturbation formulations to the higher dimensions, proposing that the
logarithmic upper and lower light cones may persist in a finite two-dimensional
system in the limit of strong disorder and weak hopping
Scale-free trees: the skeletons of complex networks
We investigate the properties of the spanning trees of various real-world and
model networks. The spanning tree representing the communication kernel of the
original network is determined by maximizing total weight of edges, whose
weights are given by the edge betweenness centralities. We find that a
scale-free tree and shortcuts organize a complex network. The spanning tree
shows robust betweenness centrality distribution that was observed in
scale-free tree models. It turns out that the shortcut distribution
characterizes the properties of original network, such as the clustering
coefficient and the classification of networks by the betweenness centrality
distribution
Neural-network quantum state study of the long-range antiferromagnetic Ising chain
We investigate quantum phase transitions in the transverse field Ising chain
with algebraically decaying long-range antiferromagnetic interactions by using
the variational Monte Carlo method with the restricted Boltzmann machine being
employed as a trial wave function ansatz. In the finite-size scaling analysis
with the order parameter and the second R\'enyi entropy, we find that the
central charge deviates from 1/2 at a small decay exponent
in contrast to the critical exponents staying very close to the short-range
(SR) Ising values regardless of examined, supporting the
previously proposed scenario of conformal invariance breakdown. To identify the
threshold of the Ising universality and the conformal symmetry, we perform two
additional tests for the universal Binder ratio and the conformal field theory
(CFT) description of the correlation function. It turns out that both indicate
a noticeable deviation from the SR Ising class at .
However, a closer look at the scaled correlation function for
shows a gradual change from the asymptotic line of
the CFT verified at , providing a rough estimate of the
threshold being in the range of
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