arXiv subjects

Ping Tang

Publications and source records attributed to Ping Tang.

At least 19 recordsLinked to original sources

arXiv2026

Pseudospin Dynamics of Charge Order

Charge order is conventionally viewed as a static modulation of the electronic density, despite growing experimental capabilities to probe and manipulate its nonequilibrium evolution. In contrast to spin-ordered systems, a microscopic framework for charge-order dynamics and its control under external driving remains largely underdeveloped. Here, starting from an extended Hubbard model, we derive an effective pseudospin model in which the charge-ordered state maps onto staggered pseudospin order. The resulting charge-order dynamics is governed by Landau--Lifshitz--Gilbert-like equations for the pseudospins, closely analogous to those of a bipartite antiferromagnet. We show that an external electric field directly controls the staggered pseudospin order and, above a threshold field, drives coherent reversal of the charge-order polarity by destabilizing collective pseudospin excitations. Our results establish the charge pseudospin as a microscopic dynamical degree of freedom for coherent switching and control of charge order, providing a charge-sector analogue of the well-established framework for spin-order dynamics in spintronics.

cond-mat.str-el↗

arXiv2026

Chirality-Selective Phonon Pumping by Ferroelectric Dynamics

The discovery of chiral phonons has expanded the conventional view of lattice vibrations as passive heat carriers, opening new opportunities for phononic spintronic devices. However, their realization has been largely limited to chiral crystals or to specific regions of momentum space in certain achiral materials. Here, we propose a generic mechanism for generating propagating chiral phonons in an ordinary dielectric through the precession of the electric polarization in an adjacent ferroelectric. The polarization dynamics transfers its intrinsic angular momentum to the lattice via electrostrictive coupling, thereby pumping chirality-selective phonons whose handedness is dictated by that of the polarization precession. For a typical LiNbO$_{3}$$|$Y$_{3}$Al$_{5}$O$_{12}$ bilayer, we find that the pumping efficiency quantified by an interfacial convertance substantially exceeds those of thermally induced chiral-phonon generation in chiral crystals, owing to the strong electrostrictive coupling in ferroelectrics. Our work establishes ferroelectric dynamics as a versatile electrical source of chiral phonons and provides a general route toward electrically programmable chiral-phononic and spintronic functionalities.

cond-mat.mes-hall↗

arXiv2026

Observation of nonlocal ferron-drag thermoelectricity

The Peltier effect induces a heat current when a charge current passes through a conductor. Since a charge current is conserved at the junction between two different conductors, the difference between the heat flowing in both conductors for the same charge current leads to heating or cooling of the interface, providing an operating mechanism of solid-state heat pumps. Here, we report observation of heat absorption and release signals even in a junction-free, homogeneous metal when placed in proximity to a ferroelectric insulator. Our experiments using active thermographic imaging techniques confirm the prediction of the ferron-drag effect, i.e., the nonlocal excitation of ferrons, the collective excitation of the ferroelectric order, by conduction electrons in the adjacent metal. We reveal the electric-polarization-direction dependence of the temperature change signals and their unexpected increase with the metal thickness beyond the charge screening length, uncovering additional electron-phonon-ferron interactions in the metal/ferroelectric hybrid structure. The discovery of crosstalk between metals and ferroelectrics via remote ferrons could become both a nuisance and an opportunity for highly integrated circuits with ferroelectric barrier materials and revolutionize the design architecture of thermoelectric devices.

cond-mat.mes-hall↗

arXiv2026

Critically Enhanced Magnon Transport in Low-dimensional Magnets

Transport properties of (quasi)particles in condensed matter depend profoundly on the spatial dimension. Motivated by recent advances in growing ultrathin magnetic films and monolayer van der Waals magnets, we present a theory of magnon transport in magnetic films spanning the crossover from bulk to the two-dimensional (2D) limit. We find a magnon conductivity that diverges~\emph{logarithmically} in magnetically soft but stable (quasi)2D magnets with long-range dipolar interactions. This critical enhancement is absent in bulk systems and may explain the unusually large magnon conductivities recently observed in ultrathin yttrium iron garnet films. Our results reveal an intrinsic mechanism for enhanced magnon transport in low dimensions and highlight the potential for engineering high-efficiency magnon conductors in atomically thin magnets.

cond-mat.mes-hall↗

arXiv2026

Thermoelectric response of a ferroelectric insulator

Thermoelectric effects enable the conversion between heat and electricity without moving parts. While conventionally associated with mobile charges, we report thermoelectricity caused by bound charges in the form of temperature changes measured by multi-harmonic lock-in thermography of a ferroelectric under an ac electric field. The observed temperature gradient depends on the field-induced displacement current, a Peltier effect in a dielectric material. Its coefficient exceeds 100 V around the ferroelectric-paraelectric phase transition, which is several orders of magnitude greater than reported values in conductors. Our findings uncover previously hidden functionalities of ferroelectric materials for thermal management by directional heat transport in ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2026

Spin-caloritronic signatures of soft magnons in bilayer CrSBr

Spin transport in magnetic insulators is often treated by assuming that magnons carry a fixed spin angular momentum of $\hbar$, which does not hold in general, however. Here we calculate the magnon spin angular momentum of a layered antiferromagnet as a function of applied magnetic field and wave vector. We show that the triaxial anisotropy and intralayer dipolar interactions in bilayer CrSBr renormalize the magnon spin angular momentum, which diverges upon field-induced magnon softening. This divergence gives rise to a pronounced peak in the thermal spin Seebeck response and provides a clear spin-caloritronic signature of soft magnons.

cond-mat.mes-hall↗

arXiv2026

Absence of Quantum-Metric-Induced Intrinsic Longitudinal Response

Nonlinear charge transport in solids has emerged as a powerful probe of the quantum geometric properties of Bloch electrons. While the Berry curvature underlies the intrinsic anomalous Hall effect, recent studies have suggested that the quantum metric may generate both \emph{intrinsic} nonlinear Hall and longitudinal transport. Here, using standard quantum-mechanical perturbation theory, we demonstrate that the quantum-metric-induced intrinsic longitudinal response identically vanishes, even though the corresponding intrinsic Hall response is allowed. This conclusion follows from the dissipationless nature of intrinsic currents and holds independently of band structure details and to all orders in the nonlinear response. Our work resolves existing inconsistencies in the theoretical formulation of quantum-metric-induced nonlinear transport and suggests a reexamination of recently reported intrinsic longitudinal responses attributed to the quantum metric.

cond-mat.mes-hall↗

arXiv2026

Emergence of Nontrivial Topological Magnon States in Skyrmionium Lattices with Zero Topological Charge

We predict the emergence of nontrivial topological magnon states in the skyrmionium lattice with zero topological charge. We propose the concept of weighted magnetic flux, which provides a clear physical picture for this anomalous phenomenon. We also map the skyrmionium lattice onto the Haldane model, offering an alternative framework for interpreting this. Our findings challenge the conventional wisdom that such states are linked to nonzero topological charge in skyrmion lattices, offering a new perspective in topological magnonics. To facilitate experimental validation, we propose two methods for preparing the skyrmionium lattice and calculate the induced magnon thermal Hall conductivity, which is a key indicator in transport measurements.

cond-mat.mes-hall↗

arXiv2026

Metasurface-based Terahertz Three-dimensional Holography Enabled by Physics-Informed Neural Network

Artificial intelligence has revolutionized optical device design, overcoming the efficiency bottlenecks of traditional methods. For holographic metasurfaces, conventional iterative algorithms suffer from time-consuming iterations and convergence stagnation, especially as the complexity of 3D target fields increases. While recent deep-learning-based algorithms have improved the trade-off between speed and image quality, most existing models remain constrained by predefined physical scenarios (e.g., fixed distances), limiting their adaptability in dynamic practical applications. To address these challenges, we propose a physics-informed neural network (PINN) based on local polynomial fitting and multi-plane wave propagation (LM-PINN) for the rapid design of terahertz 3D holographic metasurfaces. By leveraging a self-supervised training strategy, LM-PINN eliminates the need for labeled datasets, enabling direct end-to-end mapping from target holographic patterns to the metasurface structures. Both simulated and experimental results demonstrate that LM-PINN-designed metasurfaces offer higher imaging quality than traditional iterative algorithms. Crucially, by incorporating a distance encoding process, a single trained LM-PINN generalizes effectively across diverse physical configurations, including varying diffraction distances and distinct 2D or 3D targets, eliminating the necessity for retraining. Furthermore, the inference process of LM-PINN typically takes less than 1 second, providing a multifold speed advantage over traditional algorithms. Consequently, this strategy offers a robust and universal framework that paves the way for high-quality, real-time, and large-scale 3D holographic technologies.

physics.optics↗

arXiv2025

Multiferroic-like Quasiparticles in Ferroelectrics

Multiferroics are materials with coexisting electric and magnetic orders that are of central importance for fundamental research and technological applications. Unfortunately, intrinsic multiferroics that operate at room temperature remain rare due to an apparent incompatibility between magnetism and ferroelectricity. Here we predict that a pure ferroelectric support multiferroic-like quasiparticles, termed ``multiferrons", that simultaneously carry \emph{static} magnetic and electric dipoles. The electric dipole moment emerges from the parity-odd anharmonicity of the ferroelectric dynamics, while the magnetic moment has both paramagnetic and diamagnetic origins generated by circularly polarized transverse fluctuations of the ferroelectric polarization. In contrast to the established ``dynamical multiferroicity" of circularly polarized phonons, which involve only \emph{oscillating} electric dipoles, multiferrons cause, apart from Zeeman and Einstein-de Haas effects, a linear dc Stark response, giant electric-field-tunable second-harmonic generation in the THz-frequency regime, and a finite magnetoelectric cross coupling. Multiferrons open a new route toward nonlinear THz optical applications and offer multiferroic functionalities with simple ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2025

Observation of ferron transport in ferroelectrics

Ferroelectrics feature spontaneous electric dipolar order reconfigurable via electric fields. Recent theoretical studies of the collective excitations of this electric dipolar order give rise to the hope that "ferron" quasiparticles may complement the magnons of magnetic materials in information and heat management technologies. Yet direct experimental evidence of ferron transport remains elusive. Here we demonstrate efficient ferron injection and detection enabled by ferromagnetic metal contacts, achieving nonlocal signal transmission over micrometer distances in a prototypical ferroelectric PMN-PT. The transmission efficiency can be switched by external magnetic fields that couple to the contacts and gate electric fields that control the ferron excitations. Ferron-based devices open new power saving strategies that employ ferroelectric materials in a future sustainable information society.

physics.app-ph↗

arXiv2025

Exchange Surface Spin Waves in Type-A van der Waals Antiferromagnets

Surface spin waves in the short-wavelength regime enable ultrafast, nanoscale magnon-based devices. Here we report the emergence of surface spin-wave excitations within the bulk magnon band gap of type-A van der Waals antiferromagnets composed of antiferromagnetically coupled ferromagnetic monolayers. In contrast to the magnetostatic Damon-Eshbach modes in magnetic slabs, these surface waves are pure exchange modes owing to the reduced interlayer exchange coupling at surface layers, and thus persist in ultrathin multilayer stacks and at large wave numbers. We show that they can be efficiently excited by electromagnetic waves, with absorption power comparable to or even exceeding that of bulk modes. Moreover, their magnetic stray fields exhibit pronounced even-odd oscillations with the number of monolayers that should be observable by NV-center magnetometry.

cond-mat.mes-hall↗

arXiv2025

Electron hopping induced phonon pumping in opto-mechanical molecular nanocavities

Plasmonic molecular nanojunctions exhibit opto-mechanical coupling at the nanoscale, enabling intertwined optical, vibrational and electronic phenomena. Here, we demonstrate plasmon-mediated phonon pumping, driven by inelastic electron hopping in conductive molecules, which results in strong Raman nonlinearity at the light intensities almost three orders of magnitude lower than in the conventional opto-mechanical systems and up to four-fold enhancement of the effective Raman polarizability due to vibrational electron-phonon coupling, as confirmed by the significant increase in anti-Stokes Raman scattering intensity, indicating enhanced vibrational occupancy. We also developed a microscopic framework of opto-mechanical electron-phonon coupling in molecular nanojunctions based on the Marcus electron hopping. Systematically varying electrical conductance of the molecules in the junction and laser intensity, we observed the transition between a photo-assisted tunneling regime and an electron hopping process. Our findings provide a microscopic description for vibrational, optical, and electronic phenomena in plasmonic nanocavities important for efficient phonon lasing, representing the first attempt to exploit conductive molecules as quantum-mechanical oscillators.

physics.optics↗

arXiv2025

Longitudinal Spin Hall Magnetoresistance from Spin Fluctuations

Spin Hall magnetoresistance (SMR), the variation in resistance in a heavy metal (HM) with the magnetization orientation of an adjacent ferromagnet (FM), has been extensively studied as a powerful tool for probing surface magnetic moments in a variety of magnetic materials. However, the conventional SMR theory assumes rigid magnetization of a fixed magnitude, an assumption that breaks down close to the FM's Curie temperature $T_c$, where the magnetic susceptibility diverges. Here, we report an unconventional SMR effect arising from the magnetic-field modulation of spin fluctuations in the FM, while its magnetization remaining collinear to the spin Hall accumulation in the HM. In contrast to the conventional SMR, which scales with the magnetization and vanishes near $T_{c}$, such ``longitudinal" SMR (LSMR), though suppressed at low temperatures, becomes critically enhanced at $T_c$, reaching a magnitude comparable to conventional SMR amplitudes. Our findings suggest a promising method for electrically detecting enhanced spin fluctuations in magnetic systems.

cond-mat.mes-hall↗

arXiv2024

Magnon-Driven Magnetothermal Transport in Magnetic Multilayers

All-solid-state nanoscale devices capable of efficiently controlling a heat flow are crucial for advanced thermal management technologies. Here we predict a magnon-driven magnetothermal resistance (mMTR) effect in multilayers of ferromagnets and normal metals, i.e. a thermal resistance that varies when switching between parallel and antiparallel magnetization orientations of the ferromagnetic layers, even in the absence of conduction electrons in the ferromagnets. The mMTR arises from an interfacial temperature drop caused by magnon spin accumulations and can be engineered by the layer thicknesses, spin diffusion lengths, and spin conductances. The mMTR predicted here enables magnetothermal switching in insulator-based systems; we already predict large mMTR ratios up to 40$\%$ for superlattices of the electrically insulating magnet yttrium iron garnet and elemental metals.

cond-mat.mes-hall↗

arXiv2024

Role of Disorder in the Intrinsic Orbital Hall Effect

We investigate the effect of random defect scattering on the orbital Hall effect by solving a quantum Boltzmann equation. Depending on the specific orbital textures, diffuse scattering by an \emph{arbitrarily} weak disorder can affect and even fully suppress an intrinsic orbital Hall current. From the results for a simple model, we infer that disorder can play an important role in orbitronics in general.

cond-mat.mes-hall↗

arXiv2023

Electrical Injection and Transport of Coherent Magnons in Non-Collinear Antiferromagnets

Non-collinear antiferromagnets (nAFMs) with a small net magnetic moment offer new opportunities for ultrafast spintronic devices, owing to unique physical properties. While in ferromagnets and collinear AFMs the spin current polarization is locked to the magnetization $\hat{\mathbf{m}}$ and N\'eel vector $\hat{\mathbf{n}}$ directions, we predict that magnon spin currents injected by metal contacts into nAFMs can be polarized with both $\hat{\mathbf{n}}$ and $\hat{\mathbf{m}}$ components when carried by a coherent superposition of magnon eigenstates. The spin injection efficiency is governed by an interface spin conductance tensor that depends on the non-collinear magnetic texture. While the $\hat{\mathbf{m}}$-component diffuses freely into the nAFM, the $\hat{\mathbf{n}}$-component oscillates as a function of distance from the injector and applied magnetic field, analogous to the Hanle effect of electron spins in metals. Our findings reveal the potential of nAFMs as platforms for the study of tensorial coherent spin transport.

cond-mat.mes-hall↗

arXiv2023

Electric Analog of Magnons in Order-Disorder Ferroelectrics

We analyze the ``ferron" excitations in order-disorder ferroelectrics by a microscopic pseudo-spin model. We demonstrate that analogous to magnons, the quanta of spin waves in magnetic materials, ferrons carry both static and oscillating electric dipole moments, exhibit a Stark effect, and may be parametrically excited by THz radiation. The anti-crossing gap of the ferron-photon hybrid depends strongly on propagation direction and an applied static electric field. We predict ferron diffusion lengths that can reach centimeters, which implies efficient transport of electric polarization by temperature gradients. These properties suggest that ferroelectric materials may be useful for information technology beyond data storage applications.

cond-mat.mtrl-sci↗