Spin-Valley Locking in 2H-TaS2 and Its Co-Intercalated Counterpart: Roles of Surface Domains and Co Intercalation

Abstract

Tuning and probing spin-valley coupling is key to understanding correlated ground states in 2$\it{H}$-TaS$_2$. Its magnetically intercalated analogue, Co$_{1/3}$TaS$_2$, introduces additional degrees of freedom, including modified interlayer coupling and magnetism, to modulate spin-valley physics. Surface-sensitive probes like ARPES are essential for accessing surface spin texture, yet previous studies on 2$\it{H}$-TMDs have reported conflicting results regarding spin-polarized bands, leaving open whether these discrepancies are intrinsic or extrinsic. Here we performed spatially resolved spin-ARPES measurements on 2$\it{H}$-TaS$_2$ and Co$_{1/3}$TaS$_2$. Our results reveal robust spin-valley locking on both compounds. Importantly, Co intercalation enhances interlayer hybridization and introduces magnetism while preserving the TaS$_2$-derived spin texture. We further observe a spatial reversal of the out-of-plane spin polarization, which we attribute to different surface domains. This effect complicates quantifying spin textures and may underlie prior inconsistent observations. Our findings provide microscopic insight into how interlayer interactions and surface domains together govern spin-valley phenomena in layered TMDs.

Figures (5)

• Figure 1: Spin-valley locking in 2$\it{H}$-TaS$_2$.a and b, Side view (a) and top view (b) of the crystal structure of 2$\it{H}$-TaS$_2$. c, Fermi surface mapping of 2$\it{H}$-TaS$_2$ measured with 55 eV photons (left), together with the corresponding spin-polarized Fermi surface contours (right). Blue and red denote the spin-up and spin-down components of the out-of-plane spin polarization, respectively. Solid gray lines mark the Brillouin zone of 2$\it{H}$-TaS$_2$. d, Spin-integrated band structures of 2$\it{H}$-TaS$_2$ along momentum cuts A and B (as marked in c), measured at 55 eV. e, Spin-resolved energy distribution curves (EDCs) (upper panels) and corresponding spin polarizations (lower panels) taken at locations 1-5 marked in (c, d).
• Figure 2: Spin-valley locking in Co$_{1/3}$TaS$_2$.a and b, Side view (a) and top view (b) of the crystal structure of Co$_{1/3}$TaS$_2$. c, Fermi surface mapping of Co$_{0.33}$TaS$_2$ measured at 55 eV (left) and the corresponding spin-polarized Fermi surface contours (right). The dashed gray lines mark the Brillouin zone of Co$_{0.33}$TaS$_2$. d Spin-integrated band structures of Co$_{0.33}$TaS$_2$ measure at 55 eV along momentum cut A, B, and C, as marked in (c). e, Spin-resolved EDCs (upper panels) and corresponding spin polarizations (lower panels) taken at locations 1-7, as marked in (c, d).
• Figure 3: Enhanced interlayer coupling mediated by Co intercalation in Co$_{1/3}$TaS$_{2}$.a, Three-dimensional Brillouin zone of 2$\it{H}$-TaS$_2$ with high-symmetry points, and its projection onto the two-dimensional plane. b-c, Band structures of 2H-TaS$_2$ (b) and Co$_{0.33}$TaS$_{2}$ (c) along the $\rm\bar{K}_0$-$\rm\bar{M}_0$-$\rm\bar{K}_0'$ direction. Solid lines represent calculated bands based on a simple tight-binding model. The extracted values of the effective mass (m*), spin-orbit coupling strength ($\rm\Delta_{SOC}$), and interlayer coupling strength ($t_{\perp}$) are listed below each spectrum.
• Figure 4: Spatially reversed spin polarization on the surface of a Co$_{0.33}$TaS$_{2}$ sample.a, Band structures of Co$_{0.33}$TaS$_{2}$ taken along the momenta path indicated by the black curve in the inset of the leftmost panel. These spectra were acquired along a horizontal line across the sample with a step size of 0.1 mm. The coordinate $x$ of the measurement positions are labeled above each spectrum. b, Corresponding out-of-plane spin-resolved EDCs (upper panels) and spin polarizations (lower panels) taken at all positions shown in (a), at the momentum location marked by the black arrow and red cross in (a). c, Integrated spin polarization of the $\beta$ band as a function of lateral sample position $x$. d, Core-level spectra collected from all positions between x = $-$ 0.5 mm and x = + 0.2 mm. The dashed lines indicate the peak positions of the Ta 4$f_{5/2}$ and Ta 4$f_{7/2}$ orbitals. e, Schematic illustration of two adjacent layers or two rotational domains with 180$^\circ$ in-plane rotation, along with their corresponding Brillouin zones.
• Figure 5: Doping dependence of spin-resolved electronic structure in Co$_x$TaS$_2$.a-e, Spin-resolved EDCs measured on samples with Co compositions of $x$ = 0.29 (a), 0.31 (b), 0.32 (c), 0.33 (d), and 0.36 (e) are shown in upper panels. Corresponding spin polarizations are displayed in lower panels. All spectra were acquired at the same momentum location as in Fig. \ref{['fig4']}.