Experimental Evidence of Cubic Rashba Effect in an Inversion-Symmetric Oxide

We present evidence of cubic Rashba spin splitting in a quasi-two-dimensional electron gas formed at a surface of (001) SrTiO₃ single crystal from the weak localization or antilocalization (WAL) analysis of the low-temperature magnetoresistance. Our WAL data were well fitted by the model assuming mⱼ=±3/2 for the spin-split pair, in which 2π rotation of the electron wave vector k_∥ in the kₓ-ky plane accompanies 6π rotation of the spin quantization axis. This finding pertains to the p symmetry of the t2g electronic band derived from d electrons in SrTiO₃, which provides insights into the surface electronic state of (001) SrTiO₃.