1,432 research outputs found
Ground-state fidelity of the spin-1 Heisenberg chain with single ion anisotropy: quantum renormalization group and exact diagonalization approaches
We study the phase diagram of the anisotropic spin-1 Heisenberg chain with
single ion anisotropy (D) using a ground-state fidelity approach. The
ground-state fidelity and its corresponding susceptibility are calculated
within the quantum renormalization group scheme where we obtained the
renormalization of fidelity preventing to calculate the ground state. Using
this approach, the phase boundaries between the antiferromagnetic N\'{e}el,
Haldane and large-D phases are obtained for the whole phase diagram, which
justifies the application of quantum renormalization group to trace the
symmetery protected topological phases. In addition, we present numerical exact
diagonalization (Lanczos) results in, which we employ a recently introduced
non-local order parameter to locate the transition from Haldane to large-D
phase accurately.Comment: 9 pages, 11 figures, 1 table, to appear in JPC
Topological Phases of One-Dimensional Fermions: An Entanglement Point of View
The effect of interactions on topological insulators and superconductors
remains, to a large extent, an open problem. Here, we describe a framework for
classifying phases of one-dimensional interacting fermions, focusing on
spinless fermions with time-reversal symmetry and particle number parity
conservation, using concepts of entanglement. In agreement with an example
presented by Fidkowski \emph{et. al.} (Phys. Rev. B 81, 134509 (2010)), we find
that in the presence of interactions there are only eight distinct phases,
which obey a group structure. This is in contrast to the
classification in the non-interacting case. Each of these eight
phases is characterized by a unique set of bulk invariants, related to the
transformation laws of its entanglement (Schmidt) eigenstates under symmetry
operations, and has a characteristic degeneracy of its entanglement levels. If
translational symmetry is present, the number of distinct phases increases to
16.Comment: 12 pages, 1 figure; journal ref. adde
Polyethylene naphthalate film as a wavelength shifter in liquid argon detectors
Liquid argon-based scintillation detectors are important for dark matter
searches and neutrino physics. Argon scintillation light is in the vacuum
ultraviolet region, making it hard to be detected by conventional means.
Polyethylene naphthalate (PEN), an optically transparent thermoplastic
polyester commercially available as large area sheets or rolls, is proposed as
an alternative wavelength shifter to the commonly-used tetraphenyl butadiene
(TPB). By combining the existing literature data and spectrometer measurements
relative to TPB, we conclude that the fluorescence yield and timing of both
materials may be very close. The evidence collected suggests that PEN is a
suitable replacement for TPB in liquid argon neutrino detectors, and is also a
promising candidate for dark matter detectors. Advantages of PEN are discussed
in the context of scaling-up existing technologies to the next generation of
very large ktonne-scale detectors. Its simplicity has a potential to facilitate
such scale-ups, revolutionizing the field.Comment: 6 pages, 3 figure
Berry phase induced dimerization in one-dimensional quadrupolar systems
We investigate the effect of the Berry phase on quadrupoles that occur for
example in the low-energy description of spin models. Specifically we study
here the one-dimensional bilinear-biquadratic spin-one model. An open question
for many years about this model is whether it has a non-dimerized fluctuating
nematic phase. The dimerization has recently been proposed to be related to
Berry phases of the quantum fluctuations. We use an effective low-energy
description to calculate the scaling of the dimerization according to this
theory, and then verify the predictions using large scale density-matrix
renormalization group (DMRG) simulations, giving good evidence that the state
is dimerized all the way up to its transition into the ferromagnetic phase. We
furthermore discuss the multiplet structure found in the entanglement spectrum
of the ground state wave functions.Comment: 4.5 pages + 4 pages supplementary material, 4 figure
Topological phases in gapped edges of fractionalized systems
Recently, it has been proposed that exotic one-dimensional phases can be
realized by gapping out the edge states of a fractional topological insulator.
The low-energy edge degrees of freedom are described by a chain of coupled
parafermions. We introduce a classification scheme for the phases that can
occur in parafermionic chains. We find that the parafermions support both
topological symmetry fractionalized phases as well as phases in which the
parafermions condense. In the presence of additional symmetries, the phases
form a non-Abelian group. As a concrete example of the classification, we
consider the effective edge model for a fractional topological
insulator for which we calculate the entanglement spectra numerically and show
that all possible predicted phases can be realized.Comment: 11 pages, 7 figures, final versio
Boson condensation and instability in the tensor network representation of string-net states
The tensor network representation of many-body quantum states, given by local
tensors, provides a promising numerical tool for the study of strongly
correlated topological phases in two dimension. However, tensor network
representations may be vulnerable to instabilities caused by small
perturbations of the local tensor, especially when the local tensor is not
injective. For example, the topological order in tensor network representations
of the toric code ground state has been shown to be unstable under certain
small variations of the local tensor, if these small variations do not obey a
local symmetry of the tensor. In this paper, we ask the questions of
whether other types of topological orders suffer from similar kinds of
instability and if so, what is the underlying physical mechanism and whether we
can protect the order by enforcing certain symmetries on the tensor. We answer
these questions by showing that the tensor network representation of all
string-net models are indeed unstable, but the matrix product operator (MPO)
symmetries of the local tensor can help to protect the order. We find that,
`stand-alone' variations that break the MPO symmetries lead to instability
because they induce the condensation of bosonic quasi-particles and destroy the
topological order in the system. Therefore, such variations must be forbidden
for the encoded topological order to be reliably extracted from the local
tensor. On the other hand, if a tensor network based variational algorithm is
used to simulate the phase transition due to boson condensation, then such
variation directions must be allowed in order to access the continuous phase
transition process correctly.Comment: 44 pages, 85 figures, comments welcom
Let’s Talk About Money: The Role of Attachment Styles in Couples’ Financial Communication, Financial Management, and Financial Conflict
There are many households with financial problems, but most research on financial management is restricted to individual effects, not taking into account the relationship these individuals are in. The current investigation tests whether a person’s attachment style predicts how comfortable they are talking about financial issues with their partner and how that relates to different financial outcome variables. Two cross-sectional survey studies in the Netherlands and the US, each with more than 100 participants show that a higher score on anxious attachment is related to less communication about money with one’s partner. Less financial communication is related to worse financial management within the couple, which in turn predicts conflicts about money. A third survey with 770 participants shows that less financial communication is related to more financial problems. These findings highlight the need to take relationship variables into account to understand financial processes in couples
fMRI reveals a common neural substrate of illusory and real contours in V1 after perceptual learning
Perceptual learning involves the specific and relatively permanent modification of perception following a sensory experience. In psychophysical experiments, the specificity of the learning effects to the trained stimulus attributes (e.g., visual field position or stimulus orientation) is often attributed to assumed neural modifications at an early cortical site within the visual processing hierarchy. We directly investigated a neural correlate of perceptual learning in the primary visual cortex using fMRI. Twenty volunteers practiced a curvature discrimination on Kanizsa-type illusory contours in the MR scanner. Practice-induced changes in the BOLD response to illusory contours were compared between the pretraining and the posttraining block in those areas of the primary visual cortex (V1) that, in the same session, had been identified to represent real contours at corresponding visual field locations. A retinotopically specific BOLD signal increase to illusory contours was observed as a consequence of the training, possibly signaling the formation of a contour representation, which is necessary for performing the curvature discrimination. The effects of perceptual training were maintained over a period of about 10 months, and they were specific to the trained visual field position. The behavioral specificity of the learning effects supports an involvement of V1 in perceptual learning, and not in unspecific attentional effects
Symmetry protection of topological order in one-dimensional quantum spin systems
We discuss the characterization and stability of the Haldane phase in integer
spin chains on the basis of simple, physical arguments. We find that an odd-
Haldane phase is a topologically non-trivial phase which is protected by any
one of the following three global symmetries: (i) the dihedral group of
-rotations about and axes; (ii) time-reversal symmetry
; (iii) link inversion symmetry (reflection
about a bond center), consistently with previous results [Phys. Rev. B
\textbf{81}, 064439 (2010)]. On the other hand, an even- Haldane phase is
not topologically protected (i.e., it is indistinct from a trivial,
site-factorizable phase). We show some numerical evidence that supports these
claims, using concrete examples.Comment: 9 pages, 6 figures, extended version: several new examples and
numerical results added. Journal reference adde
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