6,277 research outputs found
Intertwined Orders and Electronic Structure in Superconducting Vortex Halos
We present a comprehensive study of vortex structures in -wave
superconductors from large-scale renormalized mean-field theory of the
square-lattice -- model, which has been shown to provide a
quantitative modeling for high- cuprate superconductors. With an efficient
implementation of the kernel polynomial method for solving electronic
structures, self-consistent calculations involving up to variational
parameters are performed to investigate the vortex solutions on lattices of up
to sites. By taking into account the strong correlation of the model,
our calculations shed new lights on two puzzling results that have emerged from
recent scanning tunneling microscopy (STM) experiments. The first concerns the
issue of the zero-biased-conductance peak (ZBCP) at the vortex core for a
uniform -wave superconducting state. Despite its theoretical prediction, the
ZBCP was not observed in most doping range of cuprates except in heavily
over-doped samples at low magnetic field. The second issue is the nature of the
checkerboard charge density waves (CDWs) with a period of about 8 unit cells in
the vortex halo at optimal doping. Although it has been suggested that such
bipartite structure arises from low-energy quasiparticle interference, another
intriguing scenario posits that the checkerboard CDWs originate from an
underlying bidirectional pair-density wave (PDW) ordering with the same period.
We present a coherent interpretation of these experimental results based on
systematic studies of the doping and magnetic field effects on vortex solutions
with and without a checkerboard structure. The mechanism of the emergent
intertwined orders within the vortex halo is also discussed.Comment: 19 pages, 7 figure
Generating Function for Tensor Network Diagrammatic Summation
The understanding of complex quantum many-body systems has been vastly
boosted by tensor network (TN) methods. Among others, excitation spectrum and
long-range interacting systems can be studied using TNs, where one however
confronts the intricate summation over an extensive number of tensor diagrams.
Here, we introduce a set of generating functions, which encode the diagrammatic
summations as leading order series expansion coefficients. Combined with
automatic differentiation, the generating function allows us to solve the
problem of TN diagrammatic summation. We illustrate this scheme by computing
variational excited states and dynamical structure factor of a quantum spin
chain, and further investigating entanglement properties of excited states.
Extensions to infinite size systems and higher dimension are outlined.Comment: v1: 6 pages, 2 figures. v2: published versio
Field-induced easy-axis softening of quantum ferromagnet with cubic anisotropy
In this work, we study the two-dimensional model that can lead to the
well-known cubic single-ion anisotropy along with a ferromagnetic Heisenberg
interaction under a perpendicular magnetic field. When the Heisenberg term
() is ignored, this model can be exactly solved with a reshuffled local
Hilbert space. A three-fold (two-fold) eigenstate degeneracy is found at
(), where stands for the field strength and is the strength of
cubic anisotropy. Around the second degeneracy point there is a huge gap that
separates two low-energy states from the rest three. As we turn on the
term, its leading-order contribution boils down to an effective hard-core
bosonic model as . By using the two-dimensional tensor network ansatz
we reveal that indeed various ground-state ansatz with different magnetic easy
axes possess competing energies. Our finding demonstrates that the easy axes
can be "softened" as we turn on the magnetic field for such quantum model with
cubic anisotropy, which goes beyond the mean-field analysis. Such easy-axis
softening might provide a new measure to control the magnetic orientation for
spinful semiconductors.Comment: 10 pages, 5 figures, 1 Tabl
Field-induced Bose-Einstein condensation and supersolid in the two-dimensional Kondo necklace
The application of an external magnetic field of sufficient strength to a
spin system composed of a localized singlet can overcome the energy gap and
trigger bosonic condensation and so provide an alternative method to realize
exotic phases of matter in real materials. Previous research has indicated that
a spin Hamiltonian with on-site Kondo coupling may be the effective many-body
Hamiltonian for (BNOAS) and here we
study such a Hamiltonian using a tensor network ansatz in two dimensions. Our
results unveil a phase diagram which indicates the underlying phases of BNOAS.
We propose, in response to the possible doping-induced superconductivity of
BNOAS, a fermionic model for further investigation. We hope that our discovery
can bring up further interest in both theoretical and experimental researches
for related nickelate compounds.Comment: 11 pages, 6 figures, 2 table
- …