Field-tunable nonreciprocal transport in STO/Co Heterostructures

Abstract

In systems with broken symmetry, structural asymmetry induces the Rashba-type spin-orbit interaction, which couples the spin and momentum of electrons. This nonreciprocal charge transport, induced by the Rashba-type spin-orbit interaction, can be utilized in spintronic applications and other novel device functionalities. In this study, we investigate Rashba spin- orbit coupling and asymmetric transport properties in (001) SrTiO₃ (STO)-based heterostructures. By utilizing deep reactive ion etching and surface oxygen vacancy engineering through Ar plasma treatment, we modulate surface conductivity of STO. We explore second harmonic resistance (R2ω) in heavy metal (HM)/ferromagnet (FM) bilayer structures such as STO/Co. The R2ω signal arising from nonreciprocal charge transport emerges while sweeping the magnetic field Bᵧ from -8T to 8T, which is applied perpendicular to the current. The R2ω signal shows a negative slope at low magnetic fields and a positive slope at high magnetic fields. This phenomenon occurs because both the Rashba effect at the STO two-dimensional electron gas (2DEG) and the Rashba effect at the STO/Co interface coexist in the STO/Co system. These results indicate that the interaction between Rashba effects at bulk and interface significantly influences asymmetric transport in STO/Co heterostructures.