arXiv subjects

Ruo-Yu Ning

Publications and source records attributed to Ruo-Yu Ning.

4 recordsLinked to original sources

arXiv2026

Photoinduced Odd- and Mixed-Parity Magnetism in Collinear Antiferromagnets

Altermagnetism, characterized by compensated collinear magnetic moments and even-parity momentum-dependent spin splitting, has emerged as a distinct form of magnetic order. However, realizing odd- and mixed-parity magnetism in fully compensated collinear magnets remains challenging. Here, we demonstrate light-induced odd- and mixed-parity magnetism in conventional collinear antiferromagnets. Combining Floquet theory with first-principles calculations, we show that circularly polarized light (CPL) induces odd-parity $f$-wave spin splitting in monolayer CoS and CoSe, whereas elliptically polarized light (EPL) induces $p$-wave spin splitting. Uniaxial strain combined with CPL offers an alternative route to the $p$-wave state. Furthermore, combining an electric field with CPL or EPL generates mixed-parity spin splitting. Light-induced breaking of $\mathcal{PT}$ symmetry, together with spin-orbit coupling, gives rise to a finite anomalous Hall response. Our findings establish a versatile approach to engineering spin splitting and controlling electronic and magnetic properties in compensated antiferromagnets.

cond-mat.mtrl-sci↗

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

Mirror Chern insulators in two-dimensional altermagnetic Tc$_2$Cl$_2$O and Tc$_2$Br$_2$O

The interplay between altermagnetism and crystalline band topology provides an intriguing avenue for realizing unconventional topological phases with distinctive spin-dependent properties. Here, based on first-principles calculations and theoretical analysis, we identify monolayer $\mathrm{Tc}_2X_2\mathrm{O}$ ($X$ = Cl, Br) as a family of two-dimensional altermagnetic mirror Chern insulators. In the absence of spin--orbit coupling (SOC), both monolayers exhibit robust altermagnetism with mirror-spin coupling and host two symmetry-protected Weyl points in each spin channel near the Fermi level. The Weyl points in opposite spin channels carry distinct mirror-symmetry eigenvalues, $m_z=\pm i$. Upon inclusion of SOC, the Weyl points are gapped, and the two mirror sectors acquire opposite Chern numbers, ${\cal {C}}_{+}=1$ and ${\cal {C}}_{-}=-1$, resulting in a nonzero mirror Chern number ${\cal {C}}_m=1$. A low-energy $k\cdot p$ model captures the symmetry protection of the Weyl points and elucidates their SOC-induced mass gaps and topological character. Furthermore, the resulting mirror Chern insulating phases host helical edge states within the bulk band gap and exhibit a quantized spin Hall conductivity. Our work establishes a direct connection between altermagnetism and mirror Chern topology and provides a promising platform for exploring unconventional topological and spin-dependent phenomena in two-dimensional altermagnetic materials.

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↗