Physical properties and first-principles calculations of an altermagnet candidate Cs$_{1-δ}$V$_2$Te$_2$O

TL;DR

This work reports the growth and comprehensive characterization of Cs$_{1-δ}$V$_2$Te$_2$O, a quasi-two-dimensional vanadium oxychalcogenide that exhibits a robust in-plane Néel antiferromagnetic order at $T_N oughly 293$ K. First-principles calculations reveal a Néel-type ground state with momentum-space spin splitting governed by crystal-spin symmetry, consistent with altermagnetism, and show a fully spin- and orbital-polarized V $d_{xz}$/$d_{yz}$ manifold giving quasi-one-dimensional Fermi-surface features. The combination of room-temperature antiferromagnetism, d-wave spin textures, and orbital-selective conduction points to strong potential for spintronic applications and further exploration of altermagnetism in the 1221 oxychalcogenide family.

Abstract

We report the crystal growth, structure, physical properties, and first-principles calculations of a vanadium-based oxytelluride Cs$_{1-δ}$V$_2$Te$_2$O. The material possesses two-dimensional V$_2$O square nets sandwiched by tellurium layers, with local crystallographic symmetry satisfying the spin symmetry for a $d$-wave altermagnet. An antiferromagnetic transition at 293 K is unambiguously evidenced from the measurements of magnetic susceptibility and specific heat. In addition, a secondary transition at $\sim$70 K is also observed, possibly associated with a Lifshitz transition. The first-principles calculations indicate robust Néel-type collinear antiferromagnetism in the V$_2$O plane. Consequently, spin splittings show up in momentum space, in relation with the real-space mirror/rotation symmetry. Interestingly, the V-$d_{yz}/d_{xz}$ electrons, which primarily contribute the quasi-one-dimensional Fermi surface, turns out to be fully orbital- and spin-polarized, akin to the case of a half metal. Our work lays a solid foundation on the potential applications utilizing altermagnetic properties in vanadium-based oxychalcogenides.

Figures (7)

• Figure 1: Characterizations of Cs$_{1-\delta}$V$_2$Te$_2$O ($\delta\approx$ 0.2) crystals by photography (a), EDS (b), crystal structure (c), and XRD (00$l$) diffractions at room temperature (d).
• Figure 2: Temperature dependence of in-plane resistivity for Cs$_{1-\delta}$V$_2$Te$_2$O ($\delta\approx0.2$) crystals. Anomalies are indicated with arrows at $T_{1,\rho}\approx$ 292 K and $T_{2,\rho}\approx$ 70 K, respectively, which can also be seen in the derivative plots shown in the insets.
• Figure 3: Temperature dependence of Hall coefficient of Cs$_{1-\delta}$V$_2$Te$_2$O ($\delta\approx0.2$) crystals. The error bars, derived from the linear fit of $\rho_{xy}(H)$, are smaller than the data-point size. The dashed blue lines are guides to the eye. Anomalies at $T_{1,\mathrm{Hall}}\approx$ 290 K and $T_{2,\mathrm{Hall}}\approx$ 75 K are marked, respectively. The inset shows the field dependence of Hall resistivity at representative temperatures for clarity.
• Figure 4: Temperature dependence of anisotropic magnetic susceptibility of Cs$_{1-\delta}$V$_2$Te$_2$O ($\delta\approx0.2$) crystals. The inset is a close-up for $\chi_{c}(T)$ where a small anomaly can be identified at $T_{2,\chi}\approx$ 70 K.
• Figure 5: Temperature dependence of specific heat, $C(T)$, for Cs$_{1-\delta}$V$_2$Te$_2$O ($\delta\approx0.2$) crystals. The upper left plots $C$/$T$ as a function of $T^2$ in the low-temperature regime. The upper right shows the released magnetic entropy at the AFM transition. The lower right inset shows the difference between experimental and fitted data at around $T_2=$ 70 K.