93 research outputs found
Novel Phase Between Band and Mott Insulators in Two Dimensions
We investigate the ground state phase diagram of the half-filled repulsive
Hubbard model in two dimensions in the presence of a staggered potential
, the so-called ionic Hubbard model, using cluster dynamical mean field
theory. We find that for large Coulomb repulsion, , the system is
a Mott insulator (MI). For weak to intermediate values of , on
decreasing , the Mott gap closes at a critical value beyond
which a correlated insulating phase with possible bond order (BO) is found.
Further, this phase undergoes a first-order transition to a band insulator (BI)
at with a finite charge gap at the transition. For large
, there is a direct first-order transition from a MI to a BI with a
single metallic point at the phase boundary
Cluster Dynamical Mean-Field Theory of the density-driven Mott transition in the one-dimensional Hubbard model
The one-dimensional Hubbard model is investigated by means of two different
cluster schemes suited to introduce short-range spatial correlations beyond the
single-site Dynamical Mean-Field Theory, namely the Cluster-Dynamical
Mean-Field Theory and its periodized version. It is shown that both cluster
schemes are able to describe with extreme accuracy the evolution of the density
as a function of the chemical potential from the Mott insulator to the metallic
state. Using exact diagonalization to solve the cluster impurity model, we
discuss the role of the truncation of the Hilbert space of the bath, and
propose an algorithm that gives higher weights to the low frequency
hybridization matrix elements and improves the speed of the convergence of the
algorithm.Comment: 6 pages, 4 figures, minor corrections in v
Pseudogap induced by short-range spin correlations in a doped Mott insulator
We study the evolution of a Mott-Hubbard insulator into a correlated metal
upon doping in the two-dimensional Hubbard model using the Cellular Dynamical
Mean Field Theory. Short-range spin correlations create two additional bands
apart from the familiar Hubbard bands in the spectral function. Even a tiny
doping into this insulator causes a jump of the Fermi energy to one of these
additional bands and an immediate momentum dependent suppression of the
spectral weight at this Fermi energy. The pseudogap is closely tied to the
existence of these bands. This suggests a strong-coupling mechanism that arises
from short-range spin correlations and large scattering rates for the pseudogap
phenomenon seen in several cuprates.Comment: 6 pages, 6 figure
Quality Aware Generative Adversarial Networks
Generative Adversarial Networks (GANs) have become a very popular tool for
implicitly learning high-dimensional probability distributions. Several
improvements have been made to the original GAN formulation to address some of
its shortcomings like mode collapse, convergence issues, entanglement, poor
visual quality etc. While a significant effort has been directed towards
improving the visual quality of images generated by GANs, it is rather
surprising that objective image quality metrics have neither been employed as
cost functions nor as regularizers in GAN objective functions. In this work, we
show how a distance metric that is a variant of the Structural SIMilarity
(SSIM) index (a popular full-reference image quality assessment algorithm), and
a novel quality aware discriminator gradient penalty function that is inspired
by the Natural Image Quality Evaluator (NIQE, a popular no-reference image
quality assessment algorithm) can each be used as excellent regularizers for
GAN objective functions. Specifically, we demonstrate state-of-the-art
performance using the Wasserstein GAN gradient penalty (WGAN-GP) framework over
CIFAR-10, STL10 and CelebA datasets.Comment: 10 pages, NeurIPS 201
Electron Doping of Cuprates via Interfaces with Manganites
The electron doping of undoped high- cuprates via the transfer of charge
from manganites (or other oxides) using heterostructure geometries is here
theoretically discussed. This possibility is mainly addressed via a detailed
analysis of photoemission and diffusion voltage experiments, which locate the
Fermi level of manganites above the bottom of the upper Hubbard band of some
cuprate parent compounds. A diagram with the relative location of Fermi levels
and gaps for several oxides is presented. The procedure discussed here is
generic, allowing for the qualitative prediction of the charge flow direction
at several oxide interfaces. The addition of electrons to antiferromagnetic Cu
oxides may lead to a superconducting state at the interface with minimal
quenched disorder. Model calculations using static and dynamical mean-field
theory, supplemented by a Poisson equation formalism to address charge
redistribution at the interface, support this view. The magnetic state of the
manganites could be antiferromagnetic or ferromagnetic. The former is better to
induce superconductivity than the latter, since the spin-polarized charge
transfer will be detrimental to singlet superconductivity. It is concluded that
in spite of the robust Hubbard gaps, the electron doping of undoped cuprates at
interfaces appears possible, and its realization may open an exciting area of
research in oxide heterostructures.Comment: 12 pages, 9 figure
Anomalous superconductivity and its competition with antiferromagnetism in doped Mott insulators
Proximity to a Mott insulating phase is likely to be an important physical
ingredient of a theory that aims to describe high-temperature superconductivity
in the cuprates. Quantum cluster methods are well suited to describe the Mott
phase. Hence, as a step towards a quantitative theory of the competition
between antiferromagnetism (AFM) and d-wave superconductivity (SC) in the
cuprates, we use Cellular Dynamical Mean Field Theory to compute zero
temperature properties of the two-dimensional square lattice Hubbard model. The
d-wave order parameter is found to scale like the superexchange coupling J for
on-site interaction U comparable to or larger than the bandwidth. The order
parameter also assumes a dome shape as a function of doping while, by contrast,
the gap in the single-particle density of states decreases monotonically with
increasing doping. In the presence of a finite second-neighbor hopping t', the
zero temperature phase diagram displays the electron-hole asymmetric
competition between antiferromagnetism and superconductivity that is observed
experimentally in the cuprates. Adding realistic third-neighbor hopping t''
improves the overall agreement with the experimental phase diagram. Since band
parameters can vary depending on the specific cuprate considered, the
sensitivity of the theoretical phase diagram to band parameters challenges the
commonly held assumption that the doping vs T_{c}/T_{c}^{max} phase diagram of
the cuprates is universal. The calculated ARPES spectrum displays the observed
electron-hole asymmetry. Our calculations reproduce important features of
d-wave superconductivity in the cuprates that would otherwise be considered
anomalous from the point of view of the standard BCS approach.Comment: 13 pages, 7 figure
Instagram Influencers Credibility Dimensions and Purchase Intention of Followers: Empirical Evidence
The advent of SMIs has primarily altered the means business connect with their prospects and customers. Currently, many SNSs enables SMIs to endorse the products, share opinions, provide feedback, and communicate with their followers either publicly or privately. This research aims to determine the mediating effect of loyalty of followers towards the influencer and ascribed opinion leadership on SMIs dimensions (expertise, trustworthiness, and attractiveness) and purchase intention relationship from the perspective of Instagram users in India. To measure the objective, the study acquired responses from 250 Indian Instagram users in the age group of 18-24. Results indicated that the purchase intention of followers is positively influenced by expertise, trustworthiness, ascribed opinion leadership, and loyalty of followers towards the influencer dimensions. Here, ascribed opinion leadership and loyalty of followers towards the influencer acts as an effective arbitrator between SMIs dimensions (expertise, trustworthiness, and attractiveness) and purchase intention relationship. The study suggests that before engaging SMI to promote the brand, the companies should understand the perception of followers towards the influencer in terms of expertise, attractiveness, and trustworthiness dimensions
- …