arXiv subjects

Lin-Ding Yuan

Publications and source records attributed to Lin-Ding Yuan.

11 recordsLinked to original sources

arXiv2026

A Route to Nonrelativistic Altermagnetic Spin Splitting via Ultrafast Light

We identify a nonequilibrium route for generating altermagnetic spin splitting in antiferromagnet by ultrafast light. Unlike existing strategies, this route does not require relativistic angular-momentum transfer, static symmetry breaking, or auxiliary external fields. Using real-time time-dependent density functional theory, we demonstrate in the antiferromagnetic perovskite KNiF3 that linearly polarized light can induce momentum-dependent altermagnetic spin splitting by breaking the effective time-reversal symmetry through photoexcited charge redistribution and the resulting lattice distortion. We provide a general symmetry selection rule for this route. These results establish a mechanism for ultrafast control of altermagnetism and extend its material realization into the nonequilibrium regime.

cond-mat.mtrl-sci↗

arXiv2025

Matter with apparent and hidden spin physics

Materials with interesting physical properties are often designed based on our understanding of the target physical effects. The physical properties can be either explicitly observed ("apparent") or concealed by the perceived symmetry ("hidden") but still exist. Both are enabled by specific symmetries and induced by certain physical interactions. Using the underlying approach of condensed matter theory of real materials (rather than schematic model Hamiltonians), we discuss apparent and hidden physics in real materials focusing on the properties of spin splitting and spin polarization. Depending on the enabling symmetries and underlying physical interactions, we classify spin effects into four categories with each having two subtypes; representative materials are pointed out. We then discuss the electric tunability and switch of apparent and hidden spin splitting and polarization in antiferromagnets. Finally, we extend "hidden effects" to views that are farsighted in the sense of resolving the correct atomistic and reciprocal symmetry and replaced by the incorrect higher symmetry. This framework could guide and enable systematic discovery of such intriguing effects.

cond-mat.mtrl-sci↗

arXiv2025

Ferroelectricity in antiferromagnetic wurtzite nitrides

Wurtzite-type nitrides have recently emerged as promising candidates for ferroelectric applications, yet their magnetic counterparts remain largely unexplored. Here, we establish MnSiN$_2$ and MnGeN$_2$ as aristotypes of a new multiferroic wurtzite family that simultaneously exhibits ferroelectricity and antiferromagnetism. These Mn(II)-based nitrides crystallize in polar structures and display robust G-type antiferromagnetism at room temperature. First-principles calculations reveal that nonmagnetic analogs incorporating Zn and Mg possess high polarization reversal barriers (0.735 and 0.683 eV per formula unit) and wide band gaps (4.0 and 4.8 eV), making them ideal ferroelectric candidates. In contrast, MnSiN$_2$ and MnGeN$_2$ exhibit strong antiferromagnetic exchange interactions (5--9 meV per Mn site) and moderate band gaps (1.6 and 1.0 eV), with reversal barriers of 0.963 and 0.460 eV per formula unit, respectively. Despite their limited magnetoelectric coupling, we show this family of Type-1 multiferroics exhibits altermagnetic spin splitting which reverses sign upon polarization switching. By strategically substituting alkaline-earth metals, we engineer multiple materials with coexisting switchable polarization, spin texture, and magnetic order. These findings open new avenues for the design of nitride-based altermagnetic multiferroics, offering a platform for integrated antiferromagnetic spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Octupole-driven spin torque switching of antiferromagnetic tunnel junctions

Magnetic tunnel junctions (MTJs) based on ferromagnets are canonical devices in spintronics, with wide-ranging applications in data storage, computing, and sensing. They simultaneously exhibit mechanisms for electrical detection and control of magnetic order through the tunneling magnetoresistance (TMR) and spin-transfer torque (STT) effects, respectively. It was long assumed that neither of these effects could be sizeable in all-antiferromagnetic tunnel junctions (AATJs), since they exhibit no net magnetization. Recently, however, it was shown that AATJs based on chiral antiferromagnets do exhibit TMR due to their non-relativistic momentum-dependent spin polarization and cluster magnetic octupole moment (CMO), which are manifestations of their spin-split band structure. However, the reciprocal effect, i.e., the antiferromagnetic counterpart of STT, has been assumed non-existent due to the total electric current being spin-neutral. Here, we report nanoscale AATJs exhibiting this reciprocal effect, which we term octupole-driven spin-transfer torque (OTT). We demonstrate current-induced OTT switching of PtMn3|MgO|PtMn3 AATJs, exhibiting a TMR value of 363% at room temperature and switching current densities of the order of 10 MA/cm2. Our theoretical modeling explains the origin of OTT in terms of the imbalance between intra- and inter-sublattice spin currents across the AATJ, and equivalently, in terms of the non-zero net cluster octupole polarization of each PtMn3 layer. This work establishes a new materials platform for antiferromagnetic spintronics and provides a pathway towards deeply scaled magnetic memory and room-temperature terahertz technologies.

cond-mat.mtrl-sci↗

arXiv2024

Non-relativistic spin splitting in compensated magnets that are not altermagnets

The non-relativistic spin-splitting (NRSS) of electronic bands in "altermagnets" has sparked renewed interest in antiferromagnets (AFMs) that have no net magnetization. However, altermagnets with collinear and compensated magnetism are not the only type of NRSS AFMs. In this study, we identify the symmetry conditions and characteristic signatures of a distinct group of NRSS AFMs that go beyond the description of altermagnets. These compounds exhibit a broken spin-degeneracy among the spin-polarized bands at the $\Gamma$ point in the absence of spin-orbit coupling (SOC). We use density functional theory calculations to validate these models in ternary magnetic nitrides, specifically MnXN$_2$ (X = Si, Ge, Sn), and their cation ordered variants. By removing the previous NRSS constraint on $\Gamma$, these compounds may facilitate the generation of spin currents without cancellation arising from the alternating spin polarizations. Our findings expand the scope of NRSS eligible materials.

cond-mat.mtrl-sci↗

arXiv2022

Uncovering hidden spin polarization of energy bands in antiferromagnets

Many textbook physical effects in crystals are enabled by some specific symmetries. In contrast to such "apparent effects", "hidden effect X" refers to the general condition where the nominal global system symmetry would disallow the effect X, whereas the symmetry of local sectors within the crystal would enable effect X. Known examples include the hidden Rashba and/or hidden Dresselhaus spin polarization that require spin orbit coupling, but (unlike the apparent Rashba and Dresselhaus counterparts) can exist even in inversion-symmetric non-magnetic crystals. Here we point out that the spin splitting effect that does not require spin-orbit coupling (SOC) can have a hidden spin polarization counterpart in antiferromagnets. We show that such hidden, SOC-independent effects reflect intrinsic properties of the perfect crystal rather than an effect due to imperfections, opening the possibility for experimental realization, and offering a potential way to switch antiferromagnetic ordering.

cond-mat.mtrl-sci↗

arXiv2022

Degeneracy removal of spin bands in antiferromagnets with non-interconvertible spin motif pair

Energy bands in antiferromagnets are generally spin degenerate in the absence of spin-orbit coupling (SOC). Recent studies [Physical Review B 102, 014422 (2020)] identified formal symmetry conditions for crystals for which this degeneracy can be lifted even in the zero SOC limit. Such materials could enable "spin-split" antiferromagnetic spintronics without the burden of use of heavy atom compounds. Here, we show that these formal symmetry conditions can be interpreted in terms of easy-to-visualize local motif pair, such as octahedra or tetrahedra, each carrying opposite magnetic moments. Collinear antiferromagnets with such spin motif pair whose components interconvert by neither translation nor spatial inversion will show splitting of spin bands. Such real-space motif-based approach enables an easy way to identify and design of materials having spin splitting without the need for spin orbit coupling, and offers insights on the magnitude of spin splitting.

cond-mat.mtrl-sci↗

arXiv2021

Strong influence of non-magnetic ligands on the momentum dependent spin splitting in antiferromagnets

Recent studies have shown that the non-relativistic antiferromagnetic ordering could generate momentum-dependent spin splitting analogous to the Rashba effect, but free from the requirement of relativistic spin-orbit coupling. Whereas the classification of such compounds can be illustrated by different spin-splitting prototypes (SSTs) from symmetry analysis and density functional theory calculations, the significant variation in bonding and structure of these diverse compounds representing different SSTs clouds the issue of how much of the variation in spin splitting can be traced back to the symmetry-defined characteristics, rather to the underlining chemical and structural diversity. The alternative model Hamiltonian approaches do not confront the issues of chemical and structural complexity, but often consider only the magnetic sublattice, dealing with the all-important effects of the non-magnetic ligands via renormalizing the interactions between the magnetic sites. To this end we constructed a 'DFT model Hamiltonian' that allows us to study SSTs at approximate 'constant chemistry', while retaining the realistic atomic scale structure including ligands. This is accomplished by using a single, universal magnetic skeletal lattice (Ni2+ ions in Rocksalt NiO) and designing small displacements of the non-magnetic (oxygen) sublattice which produce, by design, the different SSTs magnetic symmetries. We show that (i) even similar crystal structures having very similar band structures can lead to contrasting behavior of spin splitting vs. momentum, and (ii) even subtle deformations of the non-magnetic ligand sublattice could cause a giant spin splitting in AFM-induced SST. This is a paradigm shift relative to the convention of modeling magnets without considering the non-magnetic ligand that mediate indirect magnetic interaction (e.g., super exchange).

cond-mat.mtrl-sci↗

arXiv2020

Prediction of low-Z collinear and noncollinear antiferromagnetic compounds having momentum-dependent spin splitting even without spin-orbit coupling

Recent study (Yuan et. al., Phys. Rev. B 102, 014422 (2020)) revealed a SOC-independent spin splitting and spin polarization effect induced by antiferromagnetic ordering which do not necessarily require breaking of inversion symmetry or the presence of SOC, hence can exist even in centrosymmetric, low-Z light element compounds, considerably broadening the material base for spin polarization. In the present work we develop the magnetic symmetry conditions enabling such effect, dividing the 1651 magnetic space groups into 7 different spin splitting prototypes (SST-1 to SST-7). We use the 'Inverse Design' approach of first formulating the target property (here, spin splitting in low-Z compounds not restricted to low symmetry structures), then derive the enabling physical design principles to search realizable compounds that satisfy these a priori design principles. This process uncovers 422 magnetic space groups (160 centrosymmetric and 262 non-centrosymmetric) that could hold AFM-induced, SOC-independent spin splitting and spin polarization. We then search for stable compounds following such enabling symmetries. We investigate the electronic and spin structures of some selected prototype compounds by density functional theory (DFT) and find spin textures that are different than the traditional Rashba-Dresselhaus patterns. We provide the DFT results for all antiferromagnetic spin splitting prototypes (SST-1 to SST-4) and concentrate on revealing of the AFM-induced spin splitting prototype (SST-4). The symmetry design principles along with their transformation into an Inverse Design material search approach and DFT verification could open the way to their experimental examination.M). The symmetry design principles along with their transformation into an Inverse Design material search approach and DFT verification could open the way to their experimental examination.

cond-mat.mtrl-sci↗

arXiv2020

Giant momentum-dependent spin splitting in centrosymmetric low Z antiferromagnets

The energy vs. crystal momentum E(k) diagram for a solid (band structure) constitutes the road map for navigating its optical, magnetic, and transport properties. By selecting crystals with specific atom types, composition and symmetries, one could design a target band structure and thus desired properties. A particularly attractive outcome would be to design energy bands that are split into spin components with a momentum-dependent splitting, as envisioned by Pekar and Rashba [Zh. Eksperim. i Teor. Fiz. 47 (1964)], enabling spintronic application. The current paper provides "design principles" for wavevector dependent spin splitting (SS) of energy bands that parallels the traditional Dresselhaus and Rashba spin-orbit coupling (SOC) - induce splitting, but originates from a fundamentally different source -- antiferromagnetism. We identify a few generic AFM prototypes with distinct SS patterns using magnetic symmetry design principles. These tools allow also the identification of specific AFM compounds with SS belonging to different prototypes. A specific compound -- centrosymmetric tetragonal MnF2 -- is used via density functional band structure calculations to quantitatively illustrate one type of AFM SS. Unlike the traditional SOC-induced effects restricted to non-centrosymmetric crystals, we show that antiferromagnetic-induced spin splitting broadens the playing field to include even centrosymmetric compounds, and gives SS comparable in magnitude to the best known ('giant') SOC effects, even without SOC, and consequently does not rely on the often-unstable high atomic number elements required for high SOC. We envision that use of the current design principles to identify an optimal antiferromagnet with spin-split energy bands would be beneficial for efficient spin-charge conversion and spin orbit torque applications without the burden of requiring compounds containing heavy elements.

cond-mat.mtrl-sci↗

arXiv2018

Unified theory of the direct or indirect bandgap nature of conventional semiconductors

Although the direct or indirect nature of the bandgap transition is an essential parameter of semiconductors for optoelectronic applications, the understanding why some of the conventional semiconductors have direct or indirect bandgaps remains ambiguous. In this Letter, we revealed that the existence of the occupied cation d bands is a prime element in determining the directness of the bandgap of semiconductors through the s-d and p-d couplings, which push the conduction band energy levels at the X- and L-valley up, but leaves the Γ-valley conduction state unchanged. This unified theory unambiguously explains why Diamond, Si, Ge, and Al-containing group III-V semiconductors, which do not have active occupied d bands, have indirect bandgaps and remaining common semiconductors, except GaP, have direct bandgaps. Besides s-d and p-d couplings, bond length and electronegativity of anions are two remaining factors regulating the energy ordering of the Γ-, X-, and L-valley of the conduction band, and are responsible for the anomalous bandgap behaviors in GaN, GaP, and GaAs that have direct, indirect, and direct bandgaps, respectively, despite the fact that N, P, and As are in ascending order of the atomic number. This understanding will shed light on the design of new direct bandgap light-emitting materials.

cond-mat.mtrl-sci↗