arXiv subjects

W. Zhu

Publications and source records attributed to W. Zhu.

At least 73 records · Page 4Linked to original sources

arXiv2020

The gluon condensation effect in the cosmic hadron spectra

Hardening of cosmic proton- and nuclei-spectra is explained by using the gluon condensation (GC) model, which states that a large amount of gluons in proton may condense near the high energy threshold. The results present the GC-effect as common origin of a series of anomalous astrophysical phenomena including the broken power-law in gamma-ray spectra, the excess in positron- and electron-spectra and hardening of proton- and nuclei-spectra.

astro-ph.HE↗

arXiv2020

Quantum Hall effects of exciton condensate in topological flat bands

Tunable exciton condensates in two dimensional electron gas systems under strong magnetic field exhibits anomalous Hall transport owing to mutual Coulomb coupling, and have attracted a lot of research activity. Here, we explore another framework using topological flat band models in the absence of Landau levels, for realizing the many-body exciton phases of two-component fermions under strong intercomponent interactions. By developing new diagnosis based on the state-of-the-art density-matrix renormalization group and exact diagonalization, we show the theoretical discovery of the emergence of Halperin (111) quantum Hall effect at a total filling factor $ν=1$ in the lowest Chern band under strong Hubbard repulsion, which is classified by the unique ground state with bulk charge insulation and spin superfluidity, The topological nature is further characterized by one edge branch of chiral propagating Luttinger modes with level counting $1,1,2,3,5,7$ in consistent with the conformal field theory description. Moreover, with nearest-neighbor repulsions, we propose the Halperin (333) fractional quantum Hall effect at a total filling factor $ν=1/3$ in the lowest Chern band.

cond-mat.str-el↗

arXiv2020

COVID-19 in a social reinsurance framework: Forewarned is forearmed

The crisis caused by COVID-19 revealed the global unpreparedness to handle the impact of a pandemic. In this paper, we present a statistical analysis of the data related to the COVID-19 outbreak in China, specifically the infection speed, death and fatality rates in Hubei province. By fitting distributions of these quantities we design a parametric reinsurance contract whose trigger and cap are based on the probability distributions of the infection speed, death and fatality rates. In particular, fitting the distribution for the infection speed and death rates we provide a measure of the effectiveness of a state's action during an epidemic, and propose a reinsurance contract as a supplement to a state's social insurance to alleviate financial costs.

stat.AP↗

arXiv2020

Topological Interface between Pfaffian and anti-Pfaffian Order in $ν=5/2$ Quantum Hall Effect

Recent thermal Hall experiment pumped new energy into the problem of $ν=5/2$ quantum Hall effect, which motivated novel interpretations based on formation of mesoscopic puddles made of Pfaffian and anti-Pfaffian topological orders. Here, we study an interface between the Pfaffian and anti-Pfaffian states, which may play crucial roles in thermal transport, by means of state-of-the-art density-matrix renormalization group simulations on the cylinder geometry. We provide compelling evidences that indicate the edge modes of the Pfaffian and anti-Pfaffian state strongly hybridize with each other around the interface. Moreover, we demonstrate an intrinsic electric dipole moment emerges at the interface, similar to the "p-n" junction sandwiched between N-type and P-type semiconductor. Importantly, we elucidate the topological origin of this dipole moment, whose formation is to counterbalance the mismatch of guiding-center Hall viscosity of bulk Pfaffian and anti-Pfaffian state.

cond-mat.str-el↗

arXiv2020

Microscopic Diagnosis of Universal Geometric Responses in Fractional Quantum Hall Liquids

Topological quantum liquids contain internal degrees of freedom that are coupled to geometric response. Yet, an explicit and microscopic identification of geometric response remains difficult. Here, taking notable fractional quantum Hall (FQH) states as typical examples, we systematically investigate a promising protocol -- the Dehn twist deformation on the torus geometry, to probe the geometric response of correlated topological states and establish the relation between such response and the universal properties of pertinent states. Based on analytical derivations and numerical simulations, we find that the geometry-induced Berry phase encodes novel features for a broad class of FQH states at the Laughlin, hierarchy, Halperin and non-Abelian Moore-Read fillings. Our findings conclusively demonstrate that the adiabatic Dehn twist deformation can faithfully capture the geometry of elementary FQH droplets and intrinsic modular information including topological spin and chiral central charge. Our approach provides a powerful way to reveal topological orders of generic FQH states and allows us to address previously open questions.

cond-mat.str-el↗

arXiv2020

Continuous phase transition between bosonic integer quantum Hall liquid and trivial insulator: evidences for deconfined quantum criticality

The deconfined quantum critical point, a prototype Landau-forbidden transition, could exist in principle in the phase transitions involving symmetry protected topological phase, however, examples of such kinds of transition in physical systems are rare beyond one-dimensional systems. Here, using density-matrix renormalization group calculation, we unveil a bosonic integer quantum Hall phase in two-dimensional correlated honeycomb lattice, by full identification of its internal structure from the topological $\mathbf{K}$ matrix. Moreover we demonstrate that imbalanced periodic chemical potentials can destroy the bosonic integer quantum Hall state and drive it into a featureless trivial (Mott) insulator, where all physical observables evolve smoothly across the critical point. At the critical point the entanglement entropy reveals a characteristic scaling behavior, which is consistent with the critical field theory as an emergent QED$_3$ with two flavors of Dirac fermions.

cond-mat.str-el↗

arXiv2020

Measurement-induced phase transition: A case study in the non-integrable model by density-matrix renormalization group calculations

We study the effect of local projective measurements on the quantum quench dynamics. As a concrete example, a one-dimensional Bose-Hubbard model is simulated by the matrix product state and time-evolving block decimation. We map out a global phase diagram in terms of the measurement rate in spatial space and time domain, which demonstrates a volume-to-area law entanglement phase transition. When the measurement rate reaches the critical value, we observe a logarithmic growth of entanglement entropy as the subsystem size or evolved time increases. Moreover, we find that the probability distribution of the single-site entanglement entropy distinguishes the volume and area law phases, similar to the case of disorder-induced many-body localization. We also investigate the scaling behavior of entanglement entropy and mutual information between two separated sites, which is indicative of a single universality class and thus suggests a possible unified description of this transition.

cond-mat.stat-mech↗

arXiv2019

Electronic and Magnetic Structure of Infinite-layer $\textrm{NdNiO}_2$: Trace of Antiferromagnetic Metal

The recent discovery of Sr-doped infinite-layer nickelate $\textrm{NdNiO}_2$ [D. Li et al. Nature 572, 624 (2019)] offers an exciting platform for investigating unconventional superconductivity in nickelatebased compounds. In this work, we present a first-principles calculations for the electronic and magnetic properties of undoped parent $\textrm{NdNiO}_2$. Intriguingly, we found that: 1) the paramagnetic phase has complex Fermi pockets with 3D characters near the Fermi level; 2) by including electronelectron interactions, 3d-electrons of Ni tend to form $(π, π, π)$ antiferromagnetic ordering at low temperatures; 3) with moderate interaction strength, 5d-electrons of Nd contribute small Fermi pockets that could weaken the magnetic order akin to the self-doping effect. Our results provide a plausible interpretation for the experimentally observed resistivity minimum and Hall coefficient drop. Moreover, we elucidate that antiferromagnetic ordering in $\textrm{NdNiO}_2$ is relatively weak, arising from the small exchange coupling between 3d-electrons of Niand also hybridization with 5d-electrons of Nd.

cond-mat.str-el↗

arXiv2019

Dirac Spin Liquid on the Spin-1/2 Triangular Heisenberg Antiferromagnet

We study the spin liquid candidate of the spin-$1/2$ $J_1$-$J_2$ Heisenberg antiferromagnet on the triangular lattice by means of density matrix renormalization group (DMRG) simulations. By applying an external Aharonov-Bohm flux insertion in an infinitely long cylinder, we find unambiguous evidence for gapless $U(1)$ Dirac spin liquid behavior. The flux insertion overcomes the finite size restriction for energy gaps and clearly shows gapless behavior at the expected wave-vectors. Using the DMRG transfer matrix, the low-lying excitation spectrum can be extracted, which shows characteristic Dirac cone structures of both spinon-bilinear and monopole excitations. Finally, we confirm that the entanglement entropy follows the predicted universal response under the flux insertion.

cond-mat.str-el↗

arXiv2019

Critical Scaling Behaviors of Entanglement Spectra

We investigate the evolution of entanglement spectra under a global quantum quench from a short-range correlated state to the quantum critical point. Motivated by the conformal mapping, we find that the dynamical entanglement spectra demonstrate distinct finite-size scaling behaviors from the static case. As a prototypical example, we compute real-time dynamics of the entanglement spectra of a one-dimensional transverse-field Ising chain. Numerical simulation confirms that, the entanglement spectra scale with the subsystem size $l$ as $\sim l^{-1}$ for the dynamical equilibrium state, much faster than $\propto \log^{-1} l$ for the critical ground state. In particular, as a byproduct, the entanglement spectra at the long time limit faithfully gives universal tower structure of underlying Ising criticality, which shows the emergence of operator-state correspondence in the quantum dynamics.

cond-mat.stat-mech↗

arXiv2019

Detecting intracranial aneurysm rupture from 3D surfaces using a novel GraphNet approach

Intracranial aneurysm (IA) is a life-threatening blood spot in human's brain if it ruptures and causes cerebral hemorrhage. It is challenging to detect whether an IA has ruptured from medical images. In this paper, we propose a novel graph based neural network named GraphNet to detect IA rupture from 3D surface data. GraphNet is based on graph convolution network (GCN) and is designed for graph-level classification and node-level segmentation. The network uses GCN blocks to extract surface local features and pools to global features. 1250 patient data including 385 ruptured and 865 unruptured IAs were collected from clinic for experiments. The performance on randomly selected 234 test patient data was reported. The experiment with the proposed GraphNet achieved accuracy of 0.82, area-under-curve (AUC) of receiver operating characteristic (ROC) curve 0.82 in the classification task, significantly outperforming the baseline approach without using graph based networks. The segmentation output of the model achieved mean graph-node-based dice coefficient (DSC) score 0.88.

eess.IV↗

arXiv2019

Entanglement Hamiltonian of Many-body Dynamics in Strongly-correlated Systems

A powerful perspective in understanding non-equilibrium quantum dynamics is through the time evolution of its entanglement content. Yet apart from a few guiding principles for the entanglement entropy, to date, not much else is known about the refined characters of entanglement propagation. Here, we unveil signatures of the entanglement evolving and information propagation out-of-equilibrium, from the view of entanglement Hamiltonian. As a prototypical example, we study quantum quench dynamics of a one-dimensional Bose-Hubbard model by means of time-dependent density-matrix renormalization group simulation. Before reaching equilibration, it is found that a current operator emerges in entanglement Hamiltonian, implying that entanglement spreading is carried by particle flow. In the long-time limit subsystem enters a steady phase, evidenced by the dynamic convergence of the entanglement Hamiltonian to the expectation of a thermal ensemble. Importantly, entanglement temperature of steady state is spatially independent, which provides an intuitive trait of equilibrium. We demonstrate that these features are consistent with predictions from conformal field theory. These findings not only provide crucial information on how equilibrium statistical mechanics emerges in many-body dynamics, but also add a tool to exploring quantum dynamics from perspective of entanglement Hamiltonian.

cond-mat.str-el↗

arXiv2019

Topological characterization of hierarchical fractional quantum Hall effects in topological flat bands with SU($N$) symmetry

We study the many-body ground states of SU($N$) symmetric hardcore bosons on the topological flat-band model by using controlled numerical calculations. By introducing strong intracomponent and intercomponent interactions, we demonstrate that a hierarchy of bosonic SU($N$) fractional quantum Hall (FQH) states emerges at fractional filling factors $ν=N/(MN+1)$ (odd $M=3$). In order to characterize this series of FQH states, we figure the effective $\mathbf{K}$ matrix from the inverse of the Chern number matrix. The topological characterization of the $\mathbf{K}$ matrix also reveals quantized drag Hall responses and fractional charge pumping that could be detected in future experiments. In addition, we address the general one-to-one correspondence to the spinless FQH states in topological flat bands with Chern number $C=N$ at fillings $\widetildeν=1/(MC+1)$.

cond-mat.str-el↗

arXiv2019

CeAu$_{2}$Bi: a new nonsymmorphic antiferromagnetic compound

Here we report the structural and electronic properties of CeAu$_{2}$Bi, a new heavy-fermion compound crystallizing in a nonsymmorphic hexagonal structure ($P63/mmc$). The Ce$^{3+}$ ions form a triangular lattice which orders antiferromagnetically below $T_{N} = 3.1$~K with a magnetic hard axis along the c-axis. Under applied pressure, $T_{N}$ increases linearly at a rate of $0.07$~K/kbar, indicating that the Ce $f$-electrons are fairly localized. In fact, heat capacity measurements provide an estimate of 150(10) mJ/mol.K$^{2}$ for the Sommerfeld coefficient. The crystal-field scheme obtained from our thermodynamic data points to a ground state with dominantly $|j_{z}=\pm1/2\rangle$ character, which commonly occurs in systems with a hard c-axis. Finally, electronic band structure calculations and symmetry analysis in $k$-space reveal that CeAu$_{2}$Bi hosts symmetry-protected crossings at $k_{z} = π$ in the paramagnetic state

cond-mat.str-el↗

arXiv2019

Tomonaga-Luttinger Liquid Behavior and Spinon Confinement in YbAlO$_3$

Low dimensional quantum magnets are interesting because of the emerging collective behavior arising from strong quantum fluctuations. The one-dimensional (1D) S = 1/2 Heisenberg antiferromagnet is a paradigmatic example, whose low-energy excitations, known as spinons, carry fractional spin S = 1/2. These fractional modes can be reconfined by the application of a staggered magnetic field. Even though considerable progress has been made in the theoretical understanding of such magnets, experimental realizations of this low-dimensional physics are relatively rare. This is particularly true for rare-earth based magnets because of the large effective spin anisotropy induced by the combination of strong spin-orbit coupling and crystal field splitting. Here, we demonstrate that the rare-earth perovskite YbAlO$_3$ provides a realization of a quantum spin S = 1/2 chain material exhibiting both quantum critical Tomonaga-Luttinger liquid behavior and spinon confinement-deconfinement transitions in different regions of magnetic field-temperature phase diagram.

cond-mat.str-el↗

arXiv2018

Tunning topological phase and quantum anomalous Hall effect by interaction in quadratic band touching systems

Interaction driven topological phases can significantly enrich the class of topological materials and thus are of great importance. Here, we study the phase diagram of interacting spinless fermions filling the two-dimensional checkerboard lattice with a quadratic band touching (QBT) point. By developing new diagnosis based on the state-of-the-art density-matrix renormalization group and exact diagonalization, we determine accurate quantum phase diagram for such a system at half-filling with three distinct phases. For weak nearest-neighboring interactions, we demonstrate the instablity of the QBT towards an interaction-driven spontaneous quantum anomalous Hall (QAH) effect. For strong interactions, the system breaks the rotational symmetry realizing a nematic charge-density-wave (CDW) phase. Interestingly, for intermediate interactions we discover a symmetry-broken bond-ordered critical phase sandwiched in between the QAH and CDW phases, which splits the QBT into two Dirac points driven by interaction. Instead of the direct transition between QAH and CDW phases, our identification of an intermediate phase shed new light on the theoretical understanding of the interaction-driven phases in QBT systems.

cond-mat.str-el↗

arXiv2018

Disorder-driven transition and intermediate phase for $ν=5/2$ fractional quantum Hall effect

The fractional quantum Hall (FQH) effect at the filling number $ν=5/2$ is a primary candidate for non-Abelian topological order, while the fate of such a state in the presence of random disorder has not been resolved. Here, we address this open question by implementing unbiased diagnosis based on numerical exact diagonalization. We calculate the disorder averaged Hall conductance and the associated statistical distribution of the topological invariant Chern number, which unambiguously characterize the disorder-driven collapse of the FQH state. As the disorder strength increases towards a critical value, a continuous phase transition is detected based on the disorder configuration averaged wave function fidelity and the entanglement entropy. In the strong disorder regime, we identify a composite Fermi liquid (CFL) phase with fluctuating Chern numbers, in striking contrast to the well-known $ν=1/3$ case where an Anderson insulator appears. Interestingly, the lowest Landau level projected local density profile, the wavefunction overlap, and the entanglement entropy as a function of disorder strength simultaneously signal an intermediate phase, which may be relevant to the recent proposal of Pfaffian-anti-Pfaffian puddle state.

cond-mat.str-el↗

arXiv2018

The NANOGrav 11-year Data Set: Solar Wind Sounding Through Pulsar Timing

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has observed dozens of millisecond pulsars for over a decade. We have accrued a large collection of dispersion measure (DM) measurements sensitive to the total electron content between Earth and the pulsars at each observation. All lines of sight cross through the solar wind which produces correlated DM fluctuations in all pulsars. We develop and apply techniques for extracting the imprint of the solar wind from the full collection of DM measurements in the recently released NANOGrav 11-yr data set. We filter out long time scale DM fluctuations attributable to structure in the interstellar medium and carry out a simultaneous analysis of all pulsars in our sample that can differentiate the correlated signature of the wind from signals unique to individual lines of sight. When treating the solar wind as spherically symmetric and constant in time, we find the electron number density at 1 A.U. to be $7.9\pm0.2$ cm$^{-3}$. Our data shows little evidence of long-term variation in the density of the wind. We argue that our techniques paired with a high cadence, low radio frequency observing campaign of near-ecliptic pulsars would be capable of mapping out large-scale latitudinal structure in the wind.

astro-ph.SR↗