Realistic tight-binding model for V2Se2O-family altermagnets

Abstract

Following earlier theoretical prediction, intercalated V2Se2O-family altermagnets such as RbV2Te2O and KV2Se2O have now been experimentally confirmed as d-wave altermagnets, representing the only known van der Waals layered altermagnetic systems. By combining crystal-symmetry-paired spin-momentum locking (CSML) with the layered structure, the V2Se2O-family offers a suitable platform for studying low-dimensional spintronic responses and exploring the interplay among multiple quantum degrees of freedom. To establish a concrete theoretical foundation for understanding and utilizing these materials, we investigate six representative members of the V2Se2O-family and construct a realistic tight-binding model parameterized by first-principles calculations, which is benchmarked by experimental measurements. This model accurately captures essential altermagnetic electronic properties, including CSML and noncollinear spin-conserved currents. It further incorporates strain-coupling parameters, enabling the simulation of strain-tunable responses such as the piezo-Hall effects. This realistic model allows systematic exploration of multiple degrees of freedom (like spin, valley, and layer) within a single system, and lays the groundwork for understanding their coupling with other quantum materials, such as topological insulators and superconductors, thereby advancing both the fundamental understanding and potential device applications of this novel class of layered altermagnets.

Figures (14)

• Figure 1: Lattice and CSML for Rb-intercalated V$_2$Te$_2$O. (a) Crystal structure and Brillouin zone of Rb-intercalated V$_2$Te$_2$O, where the two sublattices are connected by $\mathcal{C}_4$ and mirror symmetries. (b)-(c) Orbital‑projected CSML band structures for (b) $d_{xz}$ orbitals with spin-up from V$_A$ and $d_{yz}$ orbitals with spin-down from V$_B$ and (c) $d_{xy}$ orbitals with spin-up from V$_A$ and $d_{xy}$ orbitals with spin-down from V$_B$. Red and blue circles refer to spin-up and spin-down, respectively.
• Figure 2: CSML band structures in the absence of SOC. Red and blue dots denote the spin-up and spin-down band structures calculated by the TB model, respectively. Results from first-principles calculations are shown as grey dots for comparison.
• Figure 3: CSML band structures in the presence of SOC. Band structures and the corresponding spin polarization ($S_z$) obtained from the TB model are represented by red and blue dots, respectively. Results from first-principles calculations are shown as grey dots for comparison.
• Figure 4: Noncollinear spin current in V$_2$X$_2$O. (a) Spin polarized current ($\boldsymbol{J^s}\parallel \boldsymbol{J^c}$) when $\boldsymbol{E}\parallel[100]$. (b) Pure spin current ($\boldsymbol{J^s}\perp \boldsymbol{J^c}$) when $\boldsymbol{E}\parallel[110]$. (c) Angle-dependent longitudinal ($\sigma^{L}$) and transverse ($\sigma^{T}$) conductivity for each spin channel, normalized by $\sigma^{\uparrow,L}(\theta=0)+\sigma^{\downarrow,L}(\theta=0)$. (d) Corresponding angle-dependent longitudinal ($\sigma^{s,L}$) and transverse ($\sigma^{s,T}$) spin conductivities. Green dashed lines mark the field angles yielding a pure spin current ($\sigma^{s,L}=0$)
• Figure 5: Electric-field control of layer polarization (a)–(c) Schematic illustration of the induced layer polarization and the corresponding non‑relativistic spin current. (d)–(f) Band projection onto the top layer. (g)–(i) Band projection onto the bottom layer. The three columns correspond to an electric field oriented along $+z$, zero, and $-z$, respectively.