Observation of the inverse spin Hall effect in the topological crystalline insulator SnTe using spin pumping

Topological crystalline insulator SnTe is a promising material for future spintronics applications because of the strong spin-orbit coupling and surface states protected by the mirror symmetry of the crystal. In this paper, using a high-quality epitaxial (001)-oriented Fe/SnTe/CdTe/ZnTe heterostructure grown on GaAs, we successfully observe the inverse spin Hall effect in SnTe induced by spin pumping, which is confirmed by detailed analyses of the dependence of the electromotive force on the microwave power, magnetic-field angle, and temperature. By a rough estimation, a relatively large spin Hall angle of ∼0.01 is obtained for bulk SnTe at room temperature. This large value may be partially caused by the surface states. Our result suggests that SnTe can be used for efficient spin-charge current conversion.

Figure 1

(a) Schematic illustration of the (001)-oriented full-epitaxial multilayer structure composed of Fe/SnTe/CdTe/ZnTe grown on a GaAs(001) substrate. The sample was cut into small pieces with a size of $3\times 0.5\mathrm{mm}$. In the electron-spin-resonance system, a rf magnetic field $h_{\mathrm{mw}}$ was applied along the $\left[\overline{1}10\right]$ direction of the sample. The out-of-plane angle of the magnetic field $H$ is defined as ${\theta }_H$ with respect to the film plane. The in-plane angle of $H$ is defined as ${\phi }_H$ with respect to the [110] direction in the film plane. (b) Mechanism of the generation of the spin current and the EMF. The vectors ${\mathbf{J}}_{\mathrm{s}}$ and $\mathbf{\sigma }$ represent the spin current and spin polarization of the spin current, respectively. Under the FMR condition of the Fe layer, the induced precession of the magnetization (M), which is represented by the thick white arrow in the Fe layer, generates a spin current. This is injected into SnTe and accumulated at a sample edge by the ISHE. (c,d) Reflection high-energy electron-diffraction patterns observed after the growth of the SnTe layer (c) and the Fe layer (d), when the electron-beam azimuth is the [110] direction. (e) X-ray-diffraction spectrum (θ-2θ scan) for the Fe/SnTe sample.

Figure 2

(a,b) Magnetic-field ${\mu }_{0}H$ dependence of the microwave absorption derivative for various ${\theta }_H$ when ${\phi }_H=0^{\circ }$ (a) and for various ${\phi }_H$ when ${\theta }_H=0^{\circ }$ (b). In (b), the gray dotted curves represent the traces of the resonance magnetic fields. (c) ${\mu }_{0}H$ dependence of the EMF for various ${\theta }_H$ when ${\phi }_H=0^{\circ }$. The black curves are fitting curves expressed by the sum of the symmetric and antisymmetric curves. (d) Higher and lower resonance magnetic fields ($H_{\mathrm{r}\_\mathrm{H}}, H_{\mathrm{r}\_\mathrm{L}}$) as a function of ${\theta }_H$ when ${\phi }_H=0^{\circ }$. (e,f) $H_{\mathrm{r}\_\mathrm{H}}$ and $H_{\mathrm{r}\_\mathrm{L}}$ as a function of ${\phi }_H$ around ${\phi }_H=0^{\circ }$ (e) and ${\phi }_H={90}^{\circ }$ (f) when ${\theta }_H=0^{\circ }$. In (d), (e), and (f), the black curves express the calculated resonance magnetic fields. All the data shown in Fig. 1 are measured at 300 K. The used power of the microwave was 200 mW.

Figure 3

(a,b) ${\mu }_{0}H$ dependences of the microwave absorption derivative (a) and the EMF (b) at various temperatures when ${\theta }_H={\phi }_H=0^{\circ }$. The used power of the microwave was 200 mW. In (b), the black curves are fitting curves expressed by the sum of the symmetric and antisymmetric curves.

Figure 4

(a) Sheet resistances of the Fe (20 nm)/SnTe (70 nm)/CdTe/ZnTe/GaAs sample (black solid curve), reference Fe (20 nm)/GaAs sample (gray curve), and reference SnTe (70 nm)/CdTe/ZnTe/GaAs sample (black broken curve). (b) Temperature dependences of $V_{\mathrm{s}\_\mathrm{L}}$ and $V_{\mathrm{s}\_\mathrm{H}}$ for the Fe (20 nm)/SnTe (70 nm)/CdTe/ZnTe/GaAs sample and for the reference Fe (20 nm)/GaAs sample. (c) Out-of-plane magnetic-field angle ${\theta }_{\mathrm{H}}$ dependence of $V_{\mathrm{s}\_\mathrm{H}}$ at 4.8 K. Here, ${\phi }_{\mathrm{H}}$ was fixed at $0^{\circ }$. In (b) and (c), the used microwave power was 200 mW. (d) ${\mu }_{0}H$ dependence of the EMF for various microwave powers at 4.8 K. The inset shows the derived symmetric and antisymmetric components ($V_{\mathrm{s}\_\mathrm{H}}, V_{\mathrm{a}\_\mathrm{H}}$) of the EMF at the higher resonance magnetic field of 107.6 mT as a function of the microwave power at 4.8 K.