arXiv subjects

Yong-Kun Wang

Publications and source records attributed to Yong-Kun Wang.

8 recordsLinked to original sources

arXiv2026

Valley- and Spin-Dependent Electronic and Transport Properties of Two-Dimensional Altermagnetic Titanium-Based Chalcogenide Halides

Altermagnets (AMs) combine fully compensated magnetization with momentum-dependent spin splitting, yet intrinsic altermagnetic materials exhibiting exceptional valley characteristics remain scarce. Here, we identify monolayer titanium-based chalcogenide halides, Ti$_2X_2Y$ ($X$ = F, Cl, Br, I; $Y$ = O, S, Se, Te), as a new family of two-dimensional altermagnetic valley materials. These monolayers exhibit robust $d$-wave altermagnetic order, semiconducting band gaps, and pronounced spin-polarized valley characteristics. We show that uniaxial strain breaks the valley degeneracy, inducing giant valley polarization together with a tunable piezomagnetic response. An in-plane electric field generates noncollinear spin currents, while spin--orbit coupling gives rise to the anomalous Hall effect, valley-selective linear dichroism, and the magneto-optical Kerr effect. These findings establish Ti$_2X_2Y$ monolayers as a versatile platform for exploring spin- and valley-dependent electronic, optical, and transport phenomena in two-dimensional altermagnets.

cond-mat.mtrl-sci↗

arXiv2026

Higher-order topological insulators in two-dimensional antiferromagnetic and altermagnetic chromium-based group-IV chalcogenides

Based on first-principles calculations combined with theoretical analysis, we identify a family of monolayer chromium-based group-IV chalcogenides as a new class of two-dimensional (2D) magnetic higher-order topological insulators (HOTIs). Specifically, the CrC$X_3$ ($X=$ S, Se, Te) and CrSiS$_3$ monolayers are found to host conventional antiferromagnetic ground states with $\mathcal{PT}$ symmetry, whereas the Janus compounds Cr$_2$C$_2$S$_3$Se$_3$ and Cr$_2$Si$_2$S$_3$Se$_3$ exhibit altermagnetic ground states. We demonstrate that all these monolayer magnetic materials realize 2D HOTI phases, in which the nontrivial topology is protected by lattice $C_3$ rotational symmetry and manifests as zero-dimensional corner states carrying quantized fractional charges. Moreover, upon inclusion of spin-orbit coupling, these systems remain in the HOTI phase and continue to host robust corner-localized states, confirming the stability of their higher-order topological nature. Our results reveal an intrinsic connection between higher-order topology and magnetic order in 2D antiferromagnetic and altermagnetic systems, identifying chromium-based group-IV chalcogenide monolayers as promising platforms for exploring higher-order topological phases and their potential relevance for future topological and spintronic applications.

cond-mat.mtrl-sci↗

arXiv2026

Electric-Field-induced Two-Dimensional Fully Compensated Ferrimagnetism and Emergent Transport Phenomena

The recent discovery of altermagnetism has demonstrated that spin-split electronic band structures can emerge in magnetic systems with zero net magnetization. In contrast, fully compensated ferrimagnetic (fFIM) systems remain far less explored, despite exhibiting similar characteristics such as vanishing magnetization and spin-split bands. Here, based on first-principles calculations combined with theoretical analysis, we demonstrate that monolayer CoS and CoSe can be driven into fFIM states by an external electric field. These materials possess collinear antiferromagnetic ground states with out-of-plane Néel vectors, and their electronic bands are spin degenerate due to $\mathcal{PT}$ symmetry. When an out-of-plane electric field is applied, $\mathcal{PT}$ symmetry is broken, inducing fFIM states with pronounced spin splitting. Moreover, we show that the resulting fFIM states host fully spin-polarized currents, anomalous Hall effects, and magneto-optical Kerr and Faraday effects. Our results establish monolayer CoS and CoSe as promising platforms for electric-field-controlled fFIM states and spintronic applications.

cond-mat.mtrl-sci↗

arXiv2026

Two-Dimensional Altermagnetic Iron Oxyhalides: Real Chern Topology and Valley-Spin-Lattice Coupling

Altermagnets, a novel class of collinear magnetic materials, exhibit unique spin-split band structures, yet topological insulating states in intrinsic altermagnetic systems are rare. Here, we identify monolayer Fe$_2X_2$O ($X$ = Cl, Br, I) as a new family of 2D altermagnetic real Chern insulators. These materials display robust $d$-wave altermagnetic ordering, semiconducting band gaps, and nontrivial real Chern numbers per spin channel, yielding spin-polarized topological corner modes. They also feature spin-polarized valleys with strong altermagnetism-valley-spin-lattice coupling, enabling valley-selective excitation via linear dichroism and strain-induced valley polarization. In multiferroic Fe$_2$Cl$_2$O, magnetism coexists with ferroelasticity, and an applied strain can switch the Néel vector. These findings position 2D iron oxyhalides as a promising platform for exploring altermagnetism and magnetic topological states for spintronics and valleytronics.

cond-mat.mtrl-sci↗

arXiv2025

Real Chern insulators in two-dimensional altermagnetic Fe$_2$S$_2$O and Fe$_2$Se$_2$O

Altermagnets, recently identified as a third class of collinear magnetic materials, have attracted significant attention in condensed matter physics. Despite this growing interest, the realization of real Chern insulators in intrinsic altermagnetic systems has rarely been reported. In this work, based on first-principles calculations and theoretical analysis, we identify monolayer Fe$_2$S$_2$O and Fe$_2$Se$_2$O as a novel class of two-dimensional altermagnetic real Chern insulators. We demonstrate that these materials possess altermagnetic ground states and host a nontrivial mirror real Chern number, leading to the emergence of symmetry-protected zero-dimensional corner states. Notably, these corner modes are spin-polarized, giving rise to a unique spin-corner coupling effect. We further show that the real Chern insulating phases and their associated corner states remain robust against spin-orbit coupling, as well as under both uniaxial and biaxial strain. Additionally, these materials exhibit pronounced linear dichroism and strong optical absorption. Our findings uncover the novel topological character of Fe$_2$S$_2$O and Fe$_2$Se$_2$O, establishing them as promising platforms for exploring real Chern insulators in altermagnetic systems.

cond-mat.mtrl-sci↗

arXiv2025

Valley-dependent electronic properties in two-dimensional altermagnetic iron-based transition metal chalcogenides

Altermagnets represent a newly identified third class of collinear magnets and have recently emerged as a focal point in condensed matter physics. In this work, through first-principles calculations and theoretical analysis, we identify monolayer Fe$_2$MoX$_4$ (X = S, Se, Te) and Fe$_2$WTe$_4$, a class of iron-based transition metal chalcogenides, as promising altermagnetic materials. These systems are found to be semiconductors exhibiting spin splitting in their nonrelativistic band structures, indicative of intrinsic altermagnetic ordering. Remarkably, their valence bands feature a pair of valleys at the time-reversal-invariant momenta X and Y points. Unlike conventional valley systems, these valleys are related by crystal symmetries rather than time-reversal symmetry. We investigate valley-dependent physical phenomena in these materials, including Berry curvature and optical circular dichroism, revealing strong valley-contrasting behavior. Furthermore, we investigate the effect of uniaxial strain and show that it effectively lifts the valley degeneracy, resulting in pronounced valley polarization. Under hole doping, this strain-induced asymmetry gives rise to a piezomagnetic response. We also explore the generation of anisotropic noncollinear spin currents in these systems, expanding the scope of their spin-related functionalities. Our findings unveil rich valley physics in monolayer Fe$_2$MoX$_4$ (X = S, Se, Te) and Fe$_2$WTe$_4$, highlighting their significant potential for applications in valleytronics, spintronics, and multifunctional nanoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Chiral Topological Phononic Quasiparticles in Enantiomeric Crystals SrSi$_2$ and BaSi$_2$

Chiral crystals have recently garnered significant interest in condensed matter physics due to their unique electronic and optical properties. In this paper, we explore the connection between the chirality of crystal structures and the chirality of topological quasiparticles. We specifically predict and analyze several chiral enantiomeric materials, such as SrSi$_2$ and BaSi$_2$, which crystallize in the chiral space groups $P4{_3}32$ and $P4{_1}32$. Based on first-principles calculations and theoretical analysis, we reveal that the phonon spectra of these materials host various topological phononic quasiparticles, including charge-2 triple points, charge-2 Dirac points, charge-2 Weyl points, and charge-1 Weyl points. Our paper shows that in these enantiomeric materials, the opposite chirality of the crystal structure results in topological quasiparticles with opposite chiral topological charges and distinct topological surface states. Our paper elucidates the intrinsic relationship between the chirality of crystal structures and the chirality of topological quasiparticles, providing promising theoretical guidance and material platform for investigating the physical properties of chiral crystals.

cond-mat.mtrl-sci↗

arXiv2024

Strain-induced valley polarization, topological states, and piezomagnetism in two-dimensional altermagnetic V$_2$Te$_2$O, V$_2$STeO, V$_2$SSeO, and V$_2$S$_2$O

Altermagnets (AM) are a recently discovered third class of collinear magnets, and have been attracting significant interest in the field of condensed matter physics. Here, based on first-principles calculations and theoretical analysis, we propose four two-dimensional (2D) magnetic materials--monolayer V$_2$Te$_2$O, V$_2$STeO, V$_2$SSeO, and V$_2$S$_2$O--as candidates for altermagnetic materials. We show that these materials are semiconductors with spin-splitting in their nonrelativistic band structures. Furthermore, in the band structure, there are a pair of Dirac-type valleys located at the time-reversal invariant momenta (TRIM) X and Y points. These two valleys are connected by crystal symmetry instead of time-reversal symmetry. We investigate the strain effect on the band structure and find that uniaxial strain can induce valley polarization, topological states in these monolayer materials. Moreover, piezomagnetism can be realized upon finite doping. Our result reveals interesting valley physics in monolayer V$_2$Te$_2$O, V$_2$STeO, V$_2$SSeO, and V$_2$S$_2$O, suggesting their great potential for valleytronics, spintronics, and multifunctional nanoelectronics applications.

cond-mat.mtrl-sci↗