Spin-Orbit Torque Induced by Switchable Crystal Inversion Symmetry Breaking.

Effective utilization and manipulation of spin-orbit torque (SOT) is crucial for developing low-power spintronic devices. Inducing additional inversion symmetry breaking (ISB) can manipulate the Rashba spin splitting and thus control the SOT generation efficiency. However, previous works mainly focus on spatial ISB at the interface introduced by the heterostructure. Effective method to introduce crystal ISB and how it impacts the SOT efficiency remains elusive. Here, we report an exotic crystal ISB in SrRuO3 (SRO) that can be reversibly manipulated by the ferroelectric (FE) polarization of the adjacent FE material. Scanning transmission electron microscopy reveals that this crystal ISB is a novel crystal distortion, i.e., c/a crystal ratio change, induced by the Ru cation's off-center displacement within the electrostatic screening depth due to the FE field. By electrical harmonic measurement, we reveal that the existence of this crystal ISB can dramatically enhance the SOT efficiency in the SRO layer by more than 60%. Our work provides an alternative to design highly efficient SOT source layer, paving the way toward low-power spintronics.