Magnetic-Field and Strain Engineering of Modulated Transverse Transport in Altermagnetic Topological Materials

Abstract

Here, we explore the role of inherent altermagnetic topology in transverse transport phenomena (such as crystal/anomalous Hall, Nernst, and thermal Hall effects) in several famous altermagnets, including tetragonal \textit{X}V$_2$\textit{Y}$_2$O (\textit{X} = K, Rb, Cs; \textit{Y} = S, Se, Te), RuO$_2$, MnF$_2$, as well as hexagonal CrSb and MnTe. Notably, in \textit{X}V$_2$\textit{Y}$_2$O, the first experimentally realized layered altermagnets, transverse transport is governed by altermagnetic pseudonodal surfaces, emphasizing the purely topological contributions to transverse transport. Interestingly, we demonstrate that strain engineering and magnetic field, two unique methods for selectively controlling crystal and anomalous transport, can substantially enhance the magnitude of these phenomena while preserving the alternating spin characteristics in both real and momentum space. Moreover, due to the spin symmetry breaking via shear strain, a new magnetic phase, fully compensated ferrimagnetism, with isotropic spin splitting, can be induced. Our findings provide effective strategies not only for manipulating transverse transport in altermagnets but also for controlling magnetic phase transitions, offering valuable insights for their potential applications in spintronics and spin caloritronics.

Figures (4)

• Figure 1: 3D first Brillouin zone (BZ) and spin-degenerate nodal surfaces for (a) XV$_2$Y$_2$O (X = K, Rb, Cs; Y = S, Se, Te) protected by [$\mathcal{C}_2||\mathcal{M}_{xy/\bar{x}y}$], (b) RuO$_2$ and MnF$_2$ protected by [$\mathcal{C}_2||\mathcal{M}_{x/y}$], (c) CrSb and $\alpha$-MnTe protected by [$\mathcal{C}_2||\mathcal{M}_{z}$] (left panel) and [$\mathcal{C}_2||\mathcal{M}_{x/x\bar{y}/y}$] (right panel), respectively.
• Figure 2: (a) Crystal structure of XV$_2$Y$_2$O. The blue and red spheres indicate the V atoms with antiparallel magnetic moment. The brown, violet, and green spheres denote nonmagnetic X, O, and Y atoms, respectively. (b) Real-space alternating spin density of XV$_2$Y$_2$O. (c-e) Reciprocal-space alternating band structures along high-symmetry points, 3D Fermi surfaces, and 3D band structures in (001) plane, of KV$_2$Se$_2$O without SOC. Red and blue lines are spin-up and spin-down bands. (f) Distribution of Berry curvature ($\Omega_{yz}$) and Fermi surfaces in the 3D BZ at the true Fermi energy. (g-i) CHC, CNC, and CTHC at $T$ = 300 K as a function of azimuthal angle when $\bm{n}$ rotates within the (001) plane.
• Figure 3: (a) Schematic illustration of the $\varepsilon_{abc}$ shear strain. Nonrelativistic band structures (b), CHC (c-d), and distribution of Berry curvature and Fermi surfaces in the 3D BZ (e-f) of KV$_2$Se$_2$O at 3% $\varepsilon_{abc}$. Here, the $\bm{n}$$\parallel$ [001] (c, e) and $\bm{n}$$\parallel$ [100] (d, f), respectively. For comparison, the CHC of RbV$_2$Te$_2$O under 3% $\varepsilon_{abc}$ are also shown in (c-d).
• Figure 4: (a) Schematic illustration of spin canting induced by an external magnetic field ($H$). (b-c) Distribution of Berry curvatures ($\Omega_{yz}$ and $\Omega_{xy}$) and Fermi surfaces in the 3D BZ for KV$_2$Se$_2$O calculated at $E_F$-0.04 eV, respectively. (d-f) Magnetic field dependence of the Hall, Nernst, and thermal Hall conductivities for KV$_2$Se$_2$O. For comparison, the black solid lines in (d-f) represent the case with canting angle of $0^\circ$, where the $\sigma_{xy}$ vanishes.