arXiv subjects

Chenglong Jia

Publications and source records attributed to Chenglong Jia.

At least 19 recordsLinked to original sources

arXiv2026

Unveiling Orbital-mediated Ultrafast Demagnetization in Rare Earth-Transition-Metal Ferrimagnets

The ultimate speed limit of magnetic recording and spintronic devices is set by the efficiency of angular-momentum transfer during ultrafast demagnetization, yet its microscopic pathway in Rare-Earth-Transition-Metal (RE-TM) ferrimagnets remains debated. Here, we establish an orbital-mediated framework in which 3d spin-orbit coupling (SOC) governs angular momentum (AM) dissipation. Strong 3d-SOC in RE-Co enables sub-picosecond, single-step demagnetization via direct orbital-to-lattice transfer, whereas weak 3d-SOC in RE-Fe redirects AM into 4f orbitals, producing slower two-step dynamics. The second-stage rate scales with 4f-SOC strength, revealing a distinct orbital-mediated dissipation channel. Using time-resolved magneto-optical Kerr measurements, supported by an extended four-temperature model, corroborate this picture across diverse RE-TM systems (RE = Sm, Gd, Tb, Dy, Ho and TM = Fe, Co, CoNi). Our results identify the SOC-driven competition between 3d and 4f orbital channels as the universal mechanism governing ultrafast demagnetization in RE-TM ferrimagnets, enabling rational design of the switching speed for next-generation spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Spin-Based True Random Number Generation Enabled by Voltage-Amplified Quantum Fluctuations

We investigate spin quantum-fluctuation effects that originate from the Heisenberg uncertainty principle during the dynamical cycle of disentanglement, entanglement, and re-disentanglement between itinerant electrons and localized magnetic moments mediated by the s-d exchange interaction. Beyond conventional deterministic spin-transfer torque, we analyze an intrinsic mechanism that transfers spin quantum fluctuations to a nanomagnet. By extending the Landau-Lifshitz-Gilbert equation to incorporate both quantum and thermal stochastic fields, we identify a temperature regime in which quantum fluctuations dominate the magnetization dynamics. We further show that voltage-controlled magnetic anisotropy exponentially amplifies spin quantum fluctuations, enabling binary readout through magnetoresistance in magnetic tunnel junctions. These findings provide a microscopic framework for fluctuation-driven spin dynamics and outline a device-level pathway toward spin-based quantum true random number generation.

cond-mat.mes-hall↗

arXiv2024

Flexomagnetoelectric effect in Sr2IrO4 thin films

Symmetry engineering is explicitly effective to manipulate and even create phases and orderings in strongly correlated materials. Flexural stress is universally practical to break the space-inversion or time-reversal symmetry. Here, by introducing strain gradient in a centrosymmetric antiferromagnet Sr2IrO4, the space-inversion symmetry is broken accompanying a non-equivalent O p-Ir d orbital hybridization along z axis. Thus, emergent polar phase and out-of-plane magnetic moment have been simultaneously observed in these asymmetric Sr2IrO4 thin films, which both are absent in its ground state. Furthermore, upon the application of magnetic field, such polarization can be controlled by modifying the occupied d orbitals through spin-orbit interaction, giving rise to a flexomagnetoelectric effect. This work provides a general strategy to artificially design multiple symmetries and ferroic orderings in strongly correlated systems.

cond-mat.str-el↗

arXiv2023

The 1/4 occupied O atoms induced ultraflat band and the one dimensional channels in the Pb$_{10-x}$Cu$_{x}$(PO$_4$)$_{6}$O$_{4}$ (x=0,0.5) crystal

The search for room-temperature superconductors has been a long-standing goal in condensed matter physics. In this study, we investigate the electronic and geometric properties of lead apatite with and without Cu doped within the frame work of the density functional theory. Based on our calculations, we found that without the Cu doped the lead apatite shows an insulator character with flat bands straddle the Fermi level. Once we introduce the O1 vacancies, the flat bands disappear. Furthermore, we analyze the effects of Cu doping on the crystal structure and electronic band structure of the material. Our calculations reveal the presence of one-dimensional channels induced by fully occupied O1 atoms, that are only 1/4 occupied in the literature, which may play a crucial role in the realization of room-temperature superconductivity. Based on our findings, we propose a possible solution to improve the quality of superconductivity by annealing the material in an oxygen atmosphere. These results contribute to a better understanding of the unusual properties of Cu-doped lead apatite and will pave the way for further exploration of its potential as a room-temperature superconductor.

cond-mat.supr-con↗

arXiv2023

Analogue gravitational lensing in optical Bose-Einstein condensates

We consider acoustic propagation of phonons in the presence of a non-rotating vortex with radial flow in a Bose-Einstein condensate (BEC) of photons. Since the vortex can be used to simulate a static acoustic black hole, the phonon would experience a considerable spacetime curvature at appreciable distance from the vortex core. The trajectory of the phonons is bended after passing by the vortex, which can be used as a simulation of gravitational lensing for phonons in a photonic BEC.

quant-ph↗

arXiv2022

Giant efficiency of long-range orbital torque in Co/Nb bilayers

We report unambiguously experimental evidence of a strong orbital current in Nb films with weak spin-orbit coupling via the spin-torque ferromagnetic resonance (ST-FMR) spectrum for Fe/Nb and Co/Nb bilayers. The sign change of the damping-like torque in Co/Nb demonstrates a large spin-orbit correlation and thus great efficiency of orbital torque in Co/Nb. By studying the efficiency as a function of the thickness of Nb sublayer, we reveal a long orbital diffusion length (~3.1 nm) of Nb. Further planar Hall resistance (PHE) measurements at positive and negative applying current confirm the nonlocal orbital transport in ferromagnetic-metal/Nb heterostructures.

physics.app-ph↗

arXiv2022

Analogue Penrose process in rotating acoustic black Hole

Analogue gravity stands today as an important tool for the investigation of gravitational phenomena that would be otherwise out of reach considering our technology. We consider here the analogue Penrose process in a rotating acoustic black hole based on a quantum fluid described by the draining bathtub model. Because of the rotating nature of this acoustic spacetime, a particle, that is a phonon travelling on the quantum fluid, will experience the well known frame dragging effect. By defining the effective Komar mass and angular momentum of this acoustic black hole, we found that energy can be extracted from it. At the same time, we show that the black hole angular momentum and mass are reduced, in complete analogy with the Penrose effect.

gr-qc↗

arXiv2022

Triple-meron crystal in high-spin Kitaev magnets

Spin textures with nontrivial topology hold great promise in future spintronics applications since they are robust against local deformations. The meron, as one of such spin textures, is widely believed to appear in pairs due to its topological equivalence to a half skyrmion. Motivated by recent progresses in high-spin Kitaev magnets, here we investigate numerically a classical Kitaev-$\Gamma$ model with a single-ion anisotropy. An exotic spin texture including three merons is discovered. Such a state features a peculiar property with an odd number of merons in one magnetic unit cell and it can induce the topological Hall effect.Therefore, these merons cannot be dissociated from skyrmions as reported in the literature and a general mechanism for such a deconfinement phenomenon calls for further studies. Our work demonstrates that high-spin Kitaev magnets can host robust unconventional spin textures and thus they offer a versatile platform not only for exploring exotic states in spintronics but also for understanding the deconfinement mechanism in the condensed-matter physics and the field theory.

cond-mat.other↗

arXiv2021

Nonreciprocal Multi-mode and Indirect Couplings in Cavity Magnonics

We investigate the magnon-photon couplings by employing a small magnet within an irregular resonant cavity, which leads to a desirable nonreciprocity with a big isolation ratio. Moreover, the higher-order couplings between the spin wave modes with the polarized photon modes also exhibit the nonreciprocity. These couplings between polarized photon and spin waves could be regarded as an indirect multi-modes coupling between the ferromagnetic resonance (FMR) mode and spin wave mode magnons mediated by the cavity mode photons. We also derive a coupling matrix to predict the characteristics of this kind of indirect coupling. The existence of the indirect couplings broaden the field range of the nonreciprocity of the system. The achieved nonreciprocal multi-mode magnon-photon couplings in a single system offer a feasible method to improve the signal transmission quality.

physics.app-ph↗

arXiv2021

Nonreciprocal Emergence of Hybridized Magnons in magnetic thin Films

We investigate the transfer and control of nonreciprocity through magnons themselves in permalloy thin films deposited on surface oxide silicon substrate. Evidences of nonreciprocal emergence of hybridized dipole exchange magnons (spin waves) at two permalloy surfaces are provided by studying magnon transmission and asymmetry, via Brillouin light scattering measurements. The dipole dominated spin wave and exchange dominated spin wave are found to be localized near the top and bottom surfaces, respectively, and traveling along opposite directions. The nonreciprocity and the localization are intertwined and ca n be tuned by an in plane magnetic field. The effects are well explained by the magnetostatic theory and can be quantitatively reproduced by the micromagnetic simulations. Our findings provide a simple and flexible approach to nonreciprocal all magnon logi c devices with highly compatible with silicon based integrated circuit technology.

cond-mat.mes-hall↗

arXiv2020

A Comprehensible Review: Magnonic Magnetoelectric Coupling in Ferroelectric/ Ferromagnetic Composites

Composite materials consisting of coupled magnetic and ferroelectric layers hold the promise for new emergent properties such as controlling magnetism with electric fields. Obviously, the interfacial coupling mechanism plays a crucial role and its understanding is the key for exploiting this material class for technological applications. This short review is focused on the magnonic-based magnetoelectric coupling that forms at the interface of a metallic ferromagnet with a ferroelectric insulator. After analyzing the physics behind this coupling, the implication for the magnetic, transport, and optical properties of these composite materials is discussed. Furthermore, examples for the functionality of such interfaces are illustrated by the electric field controlled transport through ferroelectric/ferromagnetic tunnel junctions, the electrically and magnetically controlled optical properties, and the generation of electromagnon solitons for the use as reliable information carriers.

cond-mat.mtrl-sci↗

arXiv2020

Detection of magnetic impurities using electron vortex beams

Electron microscopy stands out as electron waves providing higher spatial resolving power compared to their optical counterpart. Here we investigate theoretically the interaction of twisted electrons generated in transmission electron microscope (TEM) and magnetic impurity, in which the magnetic dipole moment is taken as a demonstration element. In addition to the usual optical phase, the inhomogeneous vector potential generated by the magnetic dipole moment makes additional contribution to the intrinsic orbital angular momentum of electrons, resulting in a Gouy phase shift. By interfering the outgoing twisted electron beam with a reference Gaussian-cylindrical wave, one can determine the magnitude and orientation of magnetic dipole directly via the rotational and deformed interference pattern. The obtained results demonstrate the usefulness of twisted electron beams for probing the atomic- and nanoscale magnetism of impurity by TEM and the proposed model provides the conceptual basis for future developments of the TEM method.

cond-mat.mes-hall↗

arXiv2020

The optical tweezer of ferroelectric skyrmions

Strong magneto-electric coupling in two-dimensional helical materials leads to a peculiar type of topologically protected solutions -- skyrmions. Coupling between the net ferroelectric polarization and magnetization allows control of the magnetic texture with an external electric field. In this work we propose the model of optical tweezer -- a particular configuration of an external electric field and Gaussian laser beam that can trap or release the skyrmions in a highly controlled manner. Functionality of such a tweezer is visualized by micromagnetic simulations and model analysis.

cond-mat.mtrl-sci↗

arXiv2019

Twisting and tweezing the spin wave: on vortices, skyrmions, helical waves, and the magnonic spiral phase plate

Spin waves are the low-energy excitations of magnetically ordered materials. They are key elements in the stability analysis of the ordered phase and have a wealth of technological applications. Recently, we showed that spin waves of a magnetic nanowire may carry a definite amount of orbital angular momentum components along the propagation direction. This helical, in addition to the chiral, character of the spin waves is related to the spatial modulations of the spin wave phase across the wire. It, however, remains a challenge to generate and control such modes with conventional magnetic fields. Here, we make the first proposal for a \textit{magnetic} spiral phase plate by appropriately synthesizing two magnetic materials that have different speeds of spin waves. It is demonstrated with full-numerical micromagnetic simulations that despite the complicated structure of demagnetization fields, a homogeneous spin wave passing through the spiral phase plate attains the required twist and propagates further with the desired orbital angular momentum. While excitations from the ordered phase may have a twist, the magnetization itself can be twisted due to internal fields and forms what is known as a magnetic vortex. We point out the differences between both types of magnetic phenomena and discuss their possible interaction.

cond-mat.mes-hall↗

arXiv2019

Non-destructive Ultrafast Steering of Magnetic Vortex by Terahertz Pulses

Electric control of magnetic vortex dynamics in a reproducible way and on an ultrafast time scale is key element in the quest for efficient spintronic devices with low-energy consumption. To be useful the control scheme should ideally be swift, scalable, non-invasive, and resulting in reliable magnetic switching. Such requirements and in particular the reproducibility of altering the vortex chirality and/or polarity are not yet met by magnetic vortex switching via external magnetic fields, spin-polarized currents, spin waves, or laser pulses. Here we demonstrate a novel packaged-skyrmion mediated vortex switching process driven by a simple sequence of picosecond electrical field pulses via magneto-electric interactions. Both the vortex chirality and polarity show a well-defined reversal behaviour. The unambiguously repeated switching between four different magnetic vortex states provides an energy-efficient, highly localized and coherent control method for non-volatile magnetic vortex-based information storage and handling.

cond-mat.mes-hall↗

arXiv2019

Square wave oscillation of soliton in double-well potential trapped BEC

We numerically investigate the soliton tunnelling process in double-well potential trapped Bose-Einstein condensate. Comparing with the usual low energy few particle tunnelling process, we find that the soliton tunnelling leads to massive particle transport between two wells. The {population imbalance} between two wells is not evolving sinusoidally with the time as the Josephson plasma oscillation, but shows a higher density contrast square-wave pattern due to the reflections at the trapping potential boundaries. Such unusual behavior clearly demonstrates the topologically stable, localized nature of solitons that propagate in a nonlinear medium without spreading. The square-wave oscillation of soliton also provides measurable dynamics to define a qubit in cold altom system.

cond-mat.quant-gas↗

arXiv2018

Topological thermal Hall effect driven by fluctuation of spin chirality in frustrated antiferromagnets

By revealing an underlying relation between the Dzyaloshinskii-Moriya interaction (DMI) and the scalar spin chirality, we develop the theory of magnon thermal Hall effects in antiferromagnetic systems. The dynamic fluctuation of the scalar chirality is shown to directly respond to the nontrivial topology of magnon bands. In materials such as the jarosites compounds KFe$_3$(OH)$_6$(SO$_4$)$_2$ and veseignite BaCu$_3$V$_2$O$_8$(OH)$_2$ in the presence of in-plane DMI, the time-reversal symmetry can be broken by the fluctuations of scalar chirality even in the case of coplanar $\mathbf{q}=0$ magnetic configuration. The spin-wave Hamiltonian is influenced by a fictitious magnetic flux determined by the in-plane DMI. Topological magnon bands and corresponding nonzero Chern numbers are presented without the need of a canted non-coplanar magnetic ordering. The canting angle dependence of thermal Hall conductivity is discussed in detail as well. These results offer a clear principle of chirality-driven topological effects in antiferromagnetically coupled systems.

cond-mat.str-el↗

arXiv2018

Time-resolved quantum spin transport through an Aharonov-Casher ring

After obtaining an exact analytical time-varying solution for the Aharonov-Casher conducting ring embedded in a textured static/dynamic electric field, we investigate the spin-resolved quantum transport in the structure. It is shown that the interference patterns are governed by not only the Aharonov-Casher geometry phase but also the instantaneous phase difference of spin precession through different traveling paths. This dynamic phase is determined by the strength of applied electric field and can have substantial effects on the charge/spin conductances, especially in the weak field regime as the period of spin precession comparable to that of the orbital motion. Our studies suggest that a low-frequency normal electric field with moderate strength possesses more degrees of freedom for manipulating the spin interference of incident electrons.

cond-mat.mes-hall↗