Spin texture in type-II Weyl semimetal ${\mathrm{WTe}}_2$

We determine the band structure and spin texture of ${\mathrm{WTe}}_2$ by spin- and angle-resolved photoemission spectroscopy (SARPES). With the support of first-principles calculations, we reveal the existence of spin polarization of both the Fermi arc surface states and bulk Fermi pockets. Our results support ${\mathrm{WTe}}_2$ to be a type-II Weyl semimetal candidate and provide important information to understand its extremely large and nonsaturating magnetoresistance.

Figure 1

(a) Three-dimensional view of the crystal structure of ${\mathrm{WTe}}_2$. The blue and orange balls represent W and Te atoms, respectively. (b) Top view, i.e., across the $\mathit{c}$ axis. The W-W zigzag chains are in the $\mathit{a}$ axis. The black rectangle indicates a surface unit cell. (c) Schematic drawing of the three-dimensional Brillouin zone (BZ) of ${\mathrm{WTe}}_2$ with the high symmetry points indicated.

Figure 2

(a) Fermi surface of ${\mathrm{WTe}}_2$ integrated within 10 meV at the Fermi level. The label “SS” marks the Fermi arc surface states. (b)–(e) ARPES intensity plots along cut 1 to cut 4 marked in (a). The green arrows in (a) and (b) indicate the bands that cross the Fermi level. (f) Schematic drawing of the Fermi surface. The blue, green, and red lines indicate the hole pockets, electron pockets, and Fermi arcs, respectively. The black dashed rectangle indicates the area measured in (a). (g) Momentum-resolved surface density of states at the Fermi level based on the contributions from the first unit cell (two triple layers). (h) Surface density of states as a function of energy along the $\mathrm{\Gamma }\text{−}X$ direction.

Figure 3

(a) Schematic drawing of the SARPES measurement configuration. (b) SARPES intensity plots $I_{\mathrm{tot}}$ along cut 5 in the laboratory frame for $S_z$, where $I_{\mathrm{tot}}=(I_{\uparrow }+I_{\downarrow })$. The green arrows indicate the bands that cross the Fermi level. (c,d) and (e,f) Spin-resolved ARPES intensity plots $I_{\mathrm{dif}}$ in the laboratory frame for $S_x$ and $S_y$ along cut 5 and cut 6, respectively. The blue and red arrows indicate the spin-up and spin-down states for each band at the Fermi level. The angle $\theta$ is ${15}^{\circ }$ for (b)–(f).

Figure 4

(a) Schematic drawing of the measured spin texture of the Fermi surface in the sample frame. (b) Calculated spin texture of the electronic states at the Fermi surface. The arrows show the horizontal spin directions, and the color scheme follows the momentum-resolved surface density of states in Fig. 2. The blue lines indicate cut 5 and cut 6 that correspond to the measurement positions. The spin polarization of the Fermi arcs and Fermi pockets is clearly found.