arXiv subjects

Jianda Wu

Publications and source records attributed to Jianda Wu.

At least 19 recordsLinked to original sources

arXiv2026

Anomalous magnetocaloric effects in the quasi-one-dimensional antiferromagnet BaCo$_2$V$_2$O$_8$

We investigate the transverse-field thermodynamics of the quasi-one-dimensional Ising-like antiferromagnet BaCo$_2$V$_2$O$_8$, whose tilted screw-chain geometry and anisotropic Land\'e $g$ tensor generate spatially modulated Zeeman couplings. Angle-resolved magnetocaloric-effect (MCE) measurements reveal a high-field temperature minimum near the transverse-field Ising critical field for $H\parallel[110]$ that persists and shifts only weakly upon field rotation. Tensor-network calculations show that the rotation-induced staggered transverse field rapidly lowers the Ising critical field and that the magnetic Gr\"uneisen ratio changes sign near the high-field temperature minimum, consistent with experiment. Our results establish that a dominant MCE response can persist away from the Ising critical region, suggesting a route to magnetic cooling by tailoring anisotropic Zeeman-coupling configurations in quantum magnets.

cond-mat.str-el↗

arXiv2026

Universal meson spectra near $(1+1)$-dimensional Ising criticality

Near $(1+1)$-dimensional [$(1+1)$D] Ising criticality, a magnetic perturbation induces confinement and produces a cascade of bound-state excitations known as mesons. Here we show these mesons share a universal mass scaling after independently rescaling the model-dependent microscopic couplings. The number of stable mesons is controlled by the lightest two-meson threshold, while the lightest-meson mass follows a continuous trajectory characterized by a single scaling parameter. Using Hamiltonian truncation method, we obtain the trajectory numerically in both Ising field theory and the near-critical mixed-field Ising chain (MFIC). Under the rescaling, the trajectory and stable-meson-count crossover windows of MFIC both collapse onto the field-theory results. To further demonstrate the above universal organization of the meson spectra, we consider a class of four-periodic spin-$1/2$ Heisenberg-Ising chains under transverse fields, whose parameter space contains a family of quantum Ising critical points. The Hamiltonian family includes effective spin models for the quasi-one-dimensional antiferromagnets Ba(Sr)Co$_2$V$_2$O$_8$. Using tensor-network calculations, we obtain the corresponding lightest-meson mass trajectory for BaCo$_2$V$_2$O$_8$ and find that it also collapse onto the same universal curve given by field-theory result. Our results suggest that the universal scaling structure of quantum Ising criticality extends into the nearby confining regime, governing the organization of the meson spectrum. They thereby provide a practical criterion for interpreting excitations of quasi-1D Ising-like magnets in mixed fields beyond $E_8$ integrability.

cond-mat.str-el↗

arXiv2026

Intertwined spin and charge dynamics in one-dimensional supersymmetric t-J model

Following the Bethe ansatz we determine the dynamical spectra of the one-dimensional supersymmetric t-J model. A series of fractionalized excitations are identified through two sets of Bethe numbers. Typical patterns in each set are found to yield wavefunctions containing elementary spin and charge carriers, manifested as distinct boundaries of the collective excitations in the spectra of single electron Green functions. In spin channels, gapless excitations fractionalized into two spin and a pair of postive and negative charge carriers, extending to finite energy as multiple continua. These patterns connect to the half-filling limit where only fractionalized spinons survive. In particle density channel, apart from spin-charge fractionalization, excitations involving only charge fluctuations are observed. Furthermore, nontrivial Bethe strings encoding bound state structure appear in channels of reducing or conserving magnetization, where spin and charge constituents can also be identified. These string states contribute significantly even to the low-energy sector in the limit of vanishing magnetization.

cond-mat.str-el↗

arXiv2025

Numerical renormalization group integrated Hamiltonian truncation: Toward generic deformation of integrable lattice models

We present a hybrid lattice Hamiltonian truncation method that integrates the numerical renormalization group (NRG) with a truncated lattice integrable spectrum. The technique is tailored for generic deformations of integrable lattice models, where the NRG enables a controlled incorporation of high-energy states. The method extends the basis set more effectively and efficiently than brute-force truncation, meanwhile significantly reducing errors. We show its capability on two paradigmatic models: an Ising chain in a magnetic field and a quantum Ising ladder. The resulting dynamical structure factors accurately capture the essential low-energy physics, including the $E_8$ and $\mathcal{D}_8^{(1)}$ excitations of the former and later models, respectively, demonstrating the approach's computational efficiency and high performance.

cond-mat.str-el↗

arXiv2025

Discrete time crystal and perfect many-body tunneling in a periodically driven Heisenberg spin chain

We investigate the non-equilibrium dynamics of a Heisenberg spin-1/2 chain driven by a periodic magnetic field. Based on its instantaneous integrability and inherent symmetry, we analytically study the magnetization and many-body tunneling (MBT). Both of them exhibit periodicity distinct from the driving period. The magnetization is shown to be independent of the initial state and robust against perturbations, signaling the formation of discrete time crystal (DTC) order. The DTC phase is found to be continuously tunable through magnetic field. The system exhibits perfect MBT, manifested as exactly vanishing Loschmidt echo (LE) thus divergent LE rate function at half period of the DTC. Remarkably, the perfect MBT is independent of the system size, and can be traced to an effective gap closure induced by quantum geometric effects. Furthermore, the Loschmidt echo spectra entropy shows logarithmic-dependence on system size, consistent with non-thermal nature of the DTC phase. We propose a protocol using ultracold atoms for experimental realization of the DTC and MBT.

cond-mat.str-el↗

arXiv2025

Nematicity in iron pnictides: phase competition and emergent symmetry

The phase diagram of iron-based superconductors contains a host of electronic orders, which are intimately connected with their superconductivity. Here we analyze the fluctuations of one type of nematic order in another. Our analysis leads to an emergent U(1) symmetry at a first-order transition between a nematic phase and a $C_4$-symmetric charge-ordered phase. We characterize the continuous symmetry in terms of a certain hidden Lie algebra that links the different orders. This emergent symmetry leads to a Goldstone mode at the transition and causes softening of excitations in the nematic and charge sectors near the transition. The underlying physics bears a resemblance to the anisotropic XZ spin model, with the nematic order and charge $C_4$ order parameters playing the roles of the $x$ and $z$ components of the magnetization vector, respectively. We provide the experimental evidence in support of the proposed effects, and discuss the general implications of our results for the physics of iron-based superconductors and other correlated systems.

cond-mat.str-el↗

arXiv2025

Berry connection and quantum geometry in time-dependent systems with instantaneous quantum integrable field theory

We study many-body quantum geometric effects in time-dependent system with emergent quantum integrable field theory instantaneously. We establish a theorem stating that the Berry connection matrix thus all associated geometric quantities of the system can be precisely characterized by excitations up to two particles from the initial quantum integrable system. To illustrate the many-body geometric influence, we analyze an Ising chain subjected to both a small longitudinal field and a slowly rotating transverse field, whose low-energy physics in the scaling limit is instantaneously governed by the quantum $E_8$ integrable field theory. Focusing on the quantum geometric potential (QGP), we show the QGP continuously suppresses the instantaneous energy gaps with decreasing longitudinal field, thereby enhancing many-body Landau-Zener tunneling as evidenced by the Loschmidt echo and its associated spectral entropy. The critical threshold for the longitudinal field strength is determined,where the spectral entropy linearly increases with system size and exhibits hyperscaling behavior when approaching to the threshold. As the longitudinal field passes the threshold and decreases toward zero, the QGP continuously leads to vanishing instantaneous energy gaps involving more low-energy excitations, resulting in increasing spectral entropy indicative of many-body Landau-Zener tunneling. Our results unveil telltale quantum geometric signatures in time-dependent many-body systems, elucidating the intricate interplay between quantum geometry and dynamics.

cond-mat.str-el↗

arXiv2025

Mesons in a quantum Ising ladder

When two transverse-field Ising chains (TFICs) with magnetic order are coupled, the original free excitations become confined, giving rise to meson-like bound states. In this work, we study such bound states systematically. The mesons are characterized by their fermion number parity and chain-exchanging properties, which lead to distinct sets of mesonic states. The meson masses are determined by solving the Bethe-Salpter equation. An interesting observation is the additional degeneracy in the chain-exchanging odd sectors. Beyond the two particle approximation, we exploit the truncated free fermionic space approach to calculate the spectrum numerically. Corrections to the meson masses are obtained, and the degeneracy is further confirmed. The characterization and degeneracy can be connected to the situation when each chain is tuned to be quantum critical, where the system is described by the Ising$_h^2$ integrable model, a sine-Gordon theory with $\mathbb{Z}_2$ orbifold. Here we establish a clear correspondence between the particles in the bosonized form and their fermionic counterparts. Near this point, the stability of these particles is analyzed using the form factor perturbation scheme, where four particles are always present. Additionally, we calculate the evolution of the dominant dynamical structure factor for local spin operators, providing further insight into the low-energy excitations and their role in the system's behavior. The two-particle confinement framework as well as the parity classifications may inspire the study for other coupled bi-partite systems.

hep-th↗

arXiv2024

Magnetization oscillations in a periodically driven transverse field Ising chain

We investigate the nonequilibrium dynamics of the magnetization in an Ising chain subjected to a slowly rotating transverse field. The magnetization oscillations are found to be explained by the contributions from different particle excitations in the quantum $E_8$ model. We study the magnetization in the frequency domain in detail, uncovering a series of singular peaks for the $z$ (Ising) component. These singular peaks are split into two sets for the magnetization along $x$ and $y$ directions with frequency shifts set by the rotational-field frequency. The peaks include both $\delta$-function type and edge-singularity type peaks. The $\delta$-function peaks can be attributed to particle excitations involving an $E_8$ particle with either the vacuum or a different particle. The edge-singularity peaks are contributed by particle excitations of two $E_8$ particles with either the vacuum or another particle, or by particle excitations that contain two sets of two particles with each set including at least a particle of the same type. We propose a Rydberg qubit array for possible experimental investigation.

cond-mat.str-el↗

arXiv2024

Thermally activated detection of dark particles in a weakly coupled quantum Ising ladder

The Ising$_h^2$ integrable field theory emerges when two quantum critical Ising chains are weakly coupled. This theory possesses eight types of relativistic particles, among which the lightest one ($B_1$) has been predicted to be a dark particle, which cannot be excited from the ground state through (quasi-)local operations. The stability on one hand highlights its potential for applications, and on the other hand makes it challenging to be observed. Here, we point out that the mass of the $B_1$ dark particle $m_{B_1}$ appears as a thermally activated gap extracted from local spin dynamical structure factor at low frequency ($\omega \ll m_{B_1}$) and low temperatures ($T \ll m_{B_1}$). We then further propose that this gapped behavior can be directly detected via the NMR relaxation rate measurement in a proper experimental setup. Our results provide a practical criterion for verifying the existence of dark particles.

cond-mat.str-el↗

arXiv2024

Emergent $D_8^{(1)}$ spectrum and topological soliton excitation in CoNb$_2$O$_6$

Quantum integrability emerging near a quantum critical point (QCP) is manifested by exotic excitation spectrum that is organized by the associated algebraic structure. A well known example is the emergent $E_8$ integrability near the QCP of a transverse field Ising chain (TFIC), which was long predicted theoretically and initially proposed to be realized in the quasi-one-dimensional (q1D) quantum magnet CoNb$_2$O$_6$. However, later measurements on the spin excitation spectrum of this material revealed a series of satellite peaks that cannot be described by the $E_8$ Lie algebra. Motivated by these experimental progresses, we hereby revisit the spin excitations of CoNb$_2$O$_6$ by combining numerical calculation and analytical analysis. We show that, as effects of strong interchain fluctuations, the spectrum of the system near the 1D QCP is characterized by the $D_{8}^{(1)}$ Lie algebra with robust topological soliton excitation. We further show that the $D_{8}^{(1)}$ spectrum can be realized in a broad class of interacting quantum systems. Our results advance the exploration of integrability and manipulation of topological excitations in quantum critical systems.

cond-mat.str-el↗

arXiv2024

Spin dynamics and dark particle in a weak-coupled quantum Ising ladder with $\mathcal{D}_8^{(1)}$ spectrum

Emergent Ising$_h^2$ integrability is anticipated in a quantum Ising ladder composed of two weakly-coupled critical transverse field Ising chains. The system is remarkable for including eight types of massive relativistic particles, with their scattering matrix and mass spectrum characterized by the $\mathcal{D}_8^{(1)}$ Lie algebra. In this article, by computing the spin dynamical structure factors following analytical form factor approach, we clearly identify dispersive single-particle excitations of (anti-) soliton and breathers as well as their multi-particle continua in the spectra, which is further confirmed by the numerical simulations. We show that the selection rule inherent in the parity and topological charge of the theory, causes a significant result that charge-parity-odd particles, termed as dark particles, cannot be directly excited from the ground state through any local or quasi-local operations. This in turn suggests the long lifetime of the lightest dark particle.

cond-mat.str-el↗

arXiv2024

Truncated string state space approach and its application to nonintegrable spin-$\frac{1}{2}$ Heisenberg chain

By circumventing the difficulty of obtaining exact string state solutions to Bethe ansatz equations, we devise a truncated string state space approach for investigating spin dynamics in a nonintegrable spin-$\frac{1}{2}$ Heisenberg chain subjected to a staggered field at various magnetizations. The obtained dynamical spectra reveal a series of elastic peaks at integer multiples of the ordering wave vector $Q$, indicating the presence of multi-$Q$ Bethe string states within the ground state. The spectrum exhibits a separation between different string continua as the strength of the staggered field increases at low magnetization, reflecting the confinement of the Bethe strings. This approach provides a unified string-state-based framework for understanding spin dynamics in low-dimensional nonintegrable Heisenberg models, which has a successful application to observations across various phases of the quasi-one-dimensional antiferromagnet $\rm YbAlO_3$.

cond-mat.str-el↗

arXiv2023

Spin dynamics of the $E_8$ particles

In this article, we report on inelastic neutron scattering measurements on a quasi-1D antiferromagnet BaCo$_2$V$_2$O$_8$ under a transverse magnetic field applied along the (0,1,0) direction. Combining results of inelastic neutron scattering experiments, analytical analysis, and numerical simulations, we precisely studied the $E_8$ excitations appearing in the whole Brillouin zone at $B_c^{1D}\approx 4.7$ T. The energy scan at $Q=(0,0,2)$ reveals a match between the data and the theoretical prediction of energies of multiple $E_8$ excitations. Furthermore, dispersions of the lightest three $E_8$ particles have been clearly observed, confirming the existence of the $E_8$ particles in BaCo$_2$V$_2$O$_8$. Our results lay down a concrete ground to systematically study the physics of the exotic $E_8$ particles.

cond-mat.str-el↗

arXiv2023

Stability and fine structure of symmetry-enriched quantum criticality in a spin ladder triangular model

In this letter, we propose and study a ladder triangular cluster model which possesses a $\mathbb{Z}_2$ symmetry and an anti-unitary $\mathbb{Z}^{\mathbb{T}}_2$ symmetry generated by the spin-flip and complex conjugation, respectively. The phase diagram of the model hosts a critical line between a spontaneous symmetry breaking phase and a symmetry protected topological phase. Along the critical line, one endpoint exhibits symmetry-enriched Ashkin-Teller universality (SEATU), while other critical points fall into the symmetry-enriched Ising universality (SEIU). Both universality classes accommodate symmetry protected degenerate edge modes under open boundary conditions. This degeneracy can be lifted with a gap opening when proper perturbation is applied to the boundary. With system size ($L$) increasing, at the point of SEATU, the gap closes following $L^{-1}$. In contrast, for the critical points of SEIU apart from a point with the known gap closing as $L^{-14}$, other points surprisingly show exponentially gap closing. The coexistence of different gap closing behaviors for critical points of the same symmetry-enriched universality goes beyond the the usual understanding of symmetry-enriched universality class, implying a fine and rich structure of phase transition and universality class.

cond-mat.str-el↗

arXiv2023

Confinement of many-body Bethe strings

Based on Bethe-ansatz approach and inelastic neutron scattering experiments, we reveal evolution of confinement of many-body Bethe strings in ordered regions of quasi-one-dimensional antiferromagnet $\rm YbAlO_3$. In the antiferromagnetic phase, the spin dynamics is dominated by the confined length-1 Bethe strings, whose dominancy in the high-energy branch of the excitation spectrum yields to the confined length-2 Bethe strings when the material is tuned to the spin-density-wave phase. In the thermal-induced disordered region, the confinement effect disappears, and the system restores the conventional quantum integrable physics of the one-dimensional Heisenberg model. Our results establish a unified picture based on Bethe string for the spin dynamics in different magnetic phases of $\rm YbAlO_3$, and thus provide profound insight into the many-body quantum magnetism.

cond-mat.str-el↗

arXiv2023

Magnetic excitations in the one-dimensional Heisenberg-Ising model with external fields and their experimental realizations

The one dimensional (1D) spin-1/2 Heisenberg-Ising model, a prototype quantum many-body system, has been intensively studied for many years. In this review, after a short introduction on some basic concepts of group theory for the octahedral group, a detailed pedagogical framework is laid down to derive the low-energy effective Hamiltonian for the Co-based materials. The 1D spin-1/2 Heisenberg-Ising model is obtained when applying the analysis to quasi-1D antiferromagnetic materials $\rm BaCo_2V_2O_8$ and $\rm SrCo_2V_2O_8$. After the preparation, we review the theoretical progresses of a variety of novel magnetic excitations and emergent physics in the 1D spin-1/2 Heisenberg-Ising model, and further summarize their recent experimental realizations.

cond-mat.str-el↗

arXiv2022

A Proposal for Detecting Superfluidity in Neutron Stars

Based on the GW dispersion relation raised in [1], we investigate the possible reflection of gravitational wave (GW) by superfluidity (SF) in the neutron star, provided its high density and dissipationless properties. Following this scenario, an experimental proposal is raised to probe the expected SF in neutron star by means of GW detection. Two types of binary systems are considered, neutron star-black hole and binary neutron star systems, with weak gravitational field condition imposed. Non-negligible modulation on the total signal caused by the GW reflection is found, which contributes amplitude and phase variations distinguishable from the primitive sine signal. Furthermore, we show that it is possible for such modulations to be detected by the Cosmic Explorer and Einstein Telescope at $100\,\mbox{Mpc}$. Identification of those signals can evince the existence of the long-sought SF in neutron stars as well as the exotic superfluidity-induced GW reflection.

gr-qc↗