arXiv subjects

Junyu Tang

Publications and source records attributed to Junyu Tang.

11 recordsLinked to original sources

arXiv2026

Non-Abelian Anyon Braiding with Quantum-Antidot Interferometry

Conventional Fabry--Perot interferometry accesses only full braids of anyons and therefore cannot directly probe the elementary $\pi$-rotation exchange. Motivated by the recent quantum-antidot proposal for the Abelian anyons, we propose an interferometry for probing the elementary exchanges of non-abelian anyons using two gate-controlled quantum antidots. By tuning two antidots independently, the device realizes distinct cooperative tunnelling processes, which correspond to different braids of non-abelian anyons. For the unresolved local fusion channels, the difference between the interference signals of the single and double cooperative processes allows us to measure the elementary exchange of the non-abelian anyons, providing a direct probe of their non-abelian statistics and topological spins. For the resolved local fusion channels, the double-cooperative process is further distinguished by a reduced interference amplitude. Our work provides a promising and practical route for manipulating and detecting non-abelian braiding with the fundamental fractional statistics.

cond-mat.mes-hall↗

arXiv2026

Phononic enhancement and detection of hidden spin-nematicity and dynamics in quantum magnets

The spin nematic phase, characterized by long-range order of spin quadrupole moments in the absence of dipolar magnetism, presents a significant challenge for conventional experimental detection. We propose a novel method to detect this elusive order in quantum magnets with an illustration in the spin-1 triangular lattice Mott insulator. By integrating out the phonon degrees of freedom, we obtain a phase diagram with substantially enlarged regions for the spin-nematic and spin-nematic-supersolid phases. We then demonstrate that through the spin-lattice coupling, the emergence of spin nematic order imprints a distinctive signature onto the phonon spectra, providing a clear spectroscopic signature for the quadrupolar order accessible via Raman or inelastic X-ray scattering. Our formalism offers a direct and powerful method to uncover the hidden spin nematicity, opening a new pathway for diagnosing multipolar orders in quantum magnets.

cond-mat.mes-hall↗

arXiv2025

Proper Theory of Magnon Orbital Angular Momentum at Equilibrium

The orbital motion of chargeless bosons, unlike that of electrons, does not generate a magnetic moment and thus cannot directly interact with magnetic fields. To formulate the orbital angular momentum (OAM) of magnons, we first identify its proper conjugate variable by considering the Aharonov-Casher effect, which gives rise to a virtual perturbation to the equilibrium state, allowing us to calculate the magnon OAM as a virtual response to an infinitesimal electric field divergence. At finite temperatures, both self-rotation and topological contributions to the magnon OAM are explicitly derived, analogous to their electronic counterpart but with the correct bosonic statistics. In a two-dimensional honeycomb lattice, we show that the Dzyaloshinskii-Moriya interaction induces a large magnon OAM in both the ferromagnetic and antiferromagnetic phases. Our formalism can be generalized to other chargeless bosons with intrinsic spin.

cond-mat.mes-hall↗

arXiv2025

Disorder-Induced Suppression of Antiferromagnetic Magnon Transport in Cr2O3

We explore the impact of spin disorder associated with structural defects on antiferromagnetic magnon transport by probing the spin-flop transition of Cr2O3 using spin Seebeck effect measurements. By fabricating homoepitaxial Cr2O3 films grown on smooth Cr2O3 crystals, we systematically vary the thickness of the films in which the presence of point defects modulates the spin-flop transition field. We find that magnon propagation through the film is entirely suppressed for film thickness greater than 3 nm, revealing the pivotal role of disorder in governing antiferromagnetic magnon transport.

cond-mat.mtrl-sci↗

arXiv2025

Coherent Spin Pumping Originated from Sub-Terahertz N\'eel Vector Dynamics in Easy Plane {\alpha}-Fe2O3/Pt

We present a thorough study of spin-to-charge current interconversion in bulk and thin films of (0001) {\alpha}-Fe2O3 /Pt heterostructures by means of all-optical polarization-controlled microwave excitation at sub-Terahertz frequencies. Our results demonstrate that coherent spin pumping is generated through excitations of both the acoustic and optical modes of antiferromagnetic resonance, provided that the corresponding selection rules are met for the relative orientation between the microwave magnetic field h_ac and the magnetic moment m_0 of the Hematite. In particular, our results unanimously show that while a microwave field with h_ac perpendicular to m_0 pumps a net spin angular momentum from the acoustic mode, spin pumping from the optical mode is only enabled when h_ac parallel to m_0, as expected from the selection rules imposed by the Neel vector dynamics. Our results support the current understanding of spin mixing conductance in antiferromagnetic/non-magnetic interfaces, contrary to recent reports where the absence of spin pumping from the optical mode in Hematite was interpreted as a cancellation effect between the diagonal and off-diagonal components of the spin mixing conductance. We also provide an explanation for the previously reported observations and show how the optical spin pumping actually vanishes for thin films, which we speculate being either due to an increased level of inhomogeneities or to insufficient film thickness for the optical mode to fully realize.

cond-mat.mes-hall↗

arXiv2024

N\'eel Spin-Orbit Torque in Antiferromagnetic Quantum Spin and Anomalous Hall Insulators

Interplay between magnetic ordering and topological electrons not only enables new topological phases but also underpins electrical control of magnetism. Here we extend the Kane-Mele model to include the exchange coupling to a collinear background antiferromagnetic (AFM) order, which can describe transition metal trichalcogenides. Owing to the spin-orbit coupling and staggered on-site potential, the system could exhibit the quantum anomalous Hall and quantum spin Hall effects in the absence of a net magnetization. Besides the chiral edge states, these topological phases support a staggered Edelstein effect through which an applied electric field can generate opposite non-equilibrium spins on the two AFM sublattices, realizing the N\'eel-type spin-orbit torque (NSOT). Contrary to known NSOTs in AFM metals driven by conduction currents, our NSOT arises from pure adiabatic currents devoid of Joule heating, while being a bulk effect not carried by the edge currents. By virtue of the NSOT, the electric field of a microwave can drive the AFM dynamics with a remarkably high efficiency. Compared to the ordinary AFM resonance driven by the magnetic field, the new mechanism can enhance the resonance amplitude by more than one order of magnitude and the absorption rate of the microwave power by over two orders of magnitude. Our findings unravel an incredible way to exploit AFM topological phases to achieve ultrafast magnetic dynamics.

cond-mat.mes-hall↗

arXiv2024

Unconventional Unidirectional Magnetoresistance in vdW Heterostructures

Electrical readout of magnetic states is a key to realize novel spintronics devices for efficient computing and data storage. Unidirectional magnetoresistance (UMR) in bilayer systems, consisting of a spin source material and a magnetic layer, refers to a change in the longitudinal resistance upon the reversal of magnetization, which typically originates from the interaction of spin-current and magnetization at the interface. Because of UMR s linear dependence on applied charge current and magnetization, it can be used to electrically read the magnetization state. However, in conventional spin source materials, the spin polarization of an electric field induced spin current is restricted to be in the film plane and hence the ensuing UMR can only respond to the in plane component of the magnetization. On the other hand, magnets with perpendicular magnetic anisotropy (PMA) are highly desired for magnetic memory and spin-logic devices, while the electrical read out of PMA magnets through UMR is critically missing. Here, we report the discovery of an unconventional UMR in bilayer heterostructures of a topological semimetal (WTe2) and a PMA ferromagnetic insulator (Cr2Ge2Te6, CGT), which allows to electrically read the up and down magnetic states of the CGT layer by measuring the longitudinal resistance. Our theoretical calculations based on a tight binding model show that the unconventional UMR originates from the interplay of crystal symmetry breaking in WTe2 and magnetic exchange interaction across the WTe2 and CGT interface. Combining with the ability of WTe2 to obtain magnetic field free switching of the PMA magnets, our discoveries open an exciting pathway to achieve two terminal magnetic memory devices that operate solely on the spin orbit torque and UMR, which is critical for developing next-generation non volatile and low power consumption data storage technologies.

cond-mat.mes-hall↗

arXiv2023

Absence of cross-sublattice spin pumping and spin-transfer torques in collinear antiferromagnets

We resolve the debate over the existence and magnitude of cross-sublattice (CS) contributions to spin pumping and spin-transfer torques in a two-sublattice antiferromagnet connected to a non-magnetic metal. Guided by symmetry considerations, we first relate the controversial CS terms to specific components in the spin conductance matrix. Then we quantify these components by studying the spin-dependent electron scattering on a fully compensated interface. We ascertain the absence of all CS contributions in the collinear regime. Even in the non-collinear regime, the CS contributions only constitute a higher-order correction to the existing theory.

cond-mat.mes-hall↗

arXiv2023

Lossless Spin-Orbit Torque in Antiferromagnetic Topological Insulator MnBi$_2$Te$_4$

We formulate and quantify the spin-orbit torque (SOT) in intrinsic antiferromagnetic topological insulator $\rm MnBi_2Te_4$ of a few septuple-layer thick, which exhibits conspicuous layer-resolved characteristics. Contrary to known current-induced torques, the SOT in insulating $\rm MnBi_2Te_4$ is driven by an electric field (or voltage). We further study the SOT-induced magnetic resonances, where in the tri-septuple-layer case we identify a peculiar exchange mode that is blind to microwaves but can be exclusively driven by the predicted SOT. As an inverse effect of the SOT, topological charge pumping generates an adiabatic current devoid of Joule heating, which occurs concomitantly with the SOT and gives rise to an overall magneto-reactance for $\rm MnBi_2Te_4$, enabling a lossless conversion of electric power into magnetic dynamics.

cond-mat.mes-hall↗

arXiv2022

Unidirectional Spin Hall Magnetoresistance in Antiferromagnetic Heterostructures

Unidirectional spin Hall magnetoresistance (USMR) has been widely reported in the heavy metal / ferromagnet (HM/FM) bilayer systems. We observe the USMR in the Pt/{\alpha}-Fe2O3 bilayers where the {\alpha}-Fe2O3 is an antiferromagnetic (AFM) insulator. Systematic field and temperature dependent measurements confirm the magnonic origin of the USMR. The appearance of AFM-USMR is driven by the imbalance of creation and annihilation of AFM magnons by spin orbit torque due to thermal random field. However, unlike its ferromagnetic counterpart, theoretical modeling reveals that the USMR in Pt/{\alpha}-Fe2O3 is determined by the antiferromagtic magnon number, and with a non-monotonic field dependence. Our findings extend the generality of the USMR which pave the ways for the highly sensitive detection of AF spin state.

cond-mat.mes-hall↗

arXiv2022

Voltage-driven exchange resonance achieving 100\% mechanical efficiency

Magnetic resonances driven by current-induced torques are crucial tools to study magnetic materials but are very limited in frequency and mechanical efficiency. We propose an alternative mechanism, voltage-induced torque, to realize high efficiency in generating high-frequency magnetization dynamics. When a ferromagnet-topological insulator-ferromagnet trilayer heterostructure is operated as an adiabatic quantum motor, voltage-induced torque arises from the adiabatic motion of gapped topological electrons on the two interfaces and act oppositely on the two ferromagnetic layers, which can excite the exchange mode where the two ferromagnetic layers precess with a $\pi$-phase difference. The exchange mode resonance, bearing a much higher frequency than the ferromagnetic resonance, is accompanied by topological charge pumping, leading to a sharp peak in electrical admittance at the resonance point. Because the output current is purely adiabatic while dissipative current vanishes identically, the proposed voltage-driven exchange resonance entails a remarkably high mechanical efficiency close to unity, which is impossible in any current-driven systems.

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