Surface-Assisted Spin Hall Effect in Au Films with Pt Impurities

We show, both experimentally and theoretically, a novel route to obtain giant room temperature spin-Hall effect due to surface-assisted skew scattering. In the experiment, we report the spin-Hall effect in Pt-doped Au films with different thicknesses $t_N$. The giant spin-Hall angle ${\gamma }_S=0.12\pm 0.04$ is obtained for $t_N=10\mathrm{nm}$ at room temperature, while it is much smaller for the $t_N=20\mathrm{nm}$ sample. Combined ab initio and quantum Monte Carlo calculations for the skew scattering due to a Pt impurity show ${\gamma }_S\cong 0.1$ on the Au (111) surface, while it is small in bulk Au. The quantum Monte Carlo results show that the spin-orbit interaction of the Pt impurity on the Au (111) surface is enhanced, because the Pt $5d$ levels are lifted to the Fermi level due to the valence fluctuation. In addition, there are two spin-orbit interaction channels on the Au (111) surface, while only one in bulk Au.

Figure 1

The resistance change of the inverse spin-Hall effect ($△R_{\mathrm{ISHE}}$) as a function of the distance ($d$) between the Hall cross and the spin injector. The Hall cross is composed of Pt-doped Au, and the concentration of Pt is 1.4 at. %. The thicknesses of the Hall crosses ($t_N$) are 10 (circles) and 20 nm (squares). The measurement was performed at room temperature. The solid and dotted lines are the results of the fitting for $t_N=10$ and 20 nm, respectively. The schematic illustration of the multiterminal device is also shown in the inset of the figure.

Figure 2

(a)–(e) are for a single Pt impurity doped in bulk Au. (a) The hybridization function between the $\xi$ orbitals of a Pt impurity and Au host, obtained in the LDA calculations. (b) The temperature times susceptibility $T{\chi }_{\xi }$, (c) the occupation number $⟨n_{\xi }⟩$, and (d) the spin-orbit correlation function $-⟨{\ell }^z{\sigma }^z⟩$ of the $\xi$ orbitals of a Pt impurity, obtained by the QMC calculations at temperature $T=360\mathrm{K}$. (e) The calculated SHA ${\gamma }_S$. (f)–(j) are the counterparts of (a)–(e), respectively, for a single Pt impurity doped on an Au (111) surface. The reasonable range of $U$ is between 1 and 2 eV, shown by vertical dashed lines. See the text for details.