Indirect experimental evidence of a persistent spin helix in H+ implanted Li-doped ZnO by photogalvanic spectroscopy

We report a large circular photogalvanic effect (CPGE) in a 2DEG created at the interface of a semiconductor/insulator homojunction at the $(10\overline{1}0)$ surface of a Li-doped ZnO microwire by low energy proton implantation. We show that the CPGE originates from the Rashba spin-orbit interaction at the interface. Our sample arrangement allows tuning the spin-orbit interaction strength by manipulating the electron spin orientation via an external magnetic field. The results of the present work obtained at 305 K indicate the experimental realization of a persistent spin helix in ZnO.