Spin-orbit coupling of Pt studied by circular dichroism in soft x-ray ARPES

Pt has a large spin-orbit coupling (SOC) and is reported to exhibit the largest spin Hall conductivity among all materials studied to date [1,2]. To establish the role of SOC in the electronic structure, we investigate the bulk electronic structure of Pt(111) using circular dichroism (spin-orbit dichroism) in soft x-ray (SX)-ARPES. We have measured band dispersions along $\Gamma$-K-X, L-W and $\Gamma$-L and the complete set of Fermi surfaces of Pt. Calculated band dispersions including SOC gives a very good match with the experimental results [2,3], thus demonstrating the role of SOC. Our results also show a $k$-dependent suppression of spin-orbit dichroism, implying a $k$-dependent quenching of the spin polarization [3]. [1] T. Kimura {\it et al.}, Phys. Rev. Lett. {\bf 98}, 156601 (2007). [2] G. Y. Guo {\it et al.}, Phys. Rev. Lett. {\bf 100}, 096401 (2008). [3] M. Gradhand {\it et al.}, Phys. Rev. B {\bf 80}, 224413 (2009).