Interfacial symmetry breaking induced spin-orbit coupling in wurtzite GaN nanowires

Applied Physics Letters, Volume 118, Issue 12, March 2021. The interfacial asymmetry-induced spin–orbit coupling (SOC) has a distinct effect on the spin relaxation and gate manipulation of spintronic devices. However, it is hard to separate the contributions from the interface and bulk by commonly used techniques, such as weak antilocalization and time-resolved Kerr rotation. Owing to the different distribution of the effective magnetic field in the momentum space, the SOC originated from the interfacial effect and the wurtzite structure inversion asymmetry (WSIA) could be distinguished by circular photo-galvanic effect (CPGE) measurements. In this work, the angle and external gate-voltage dependences of the interfacial SOC in GaN nanowires (NWs) were investigated using the CPGE. The interfacial SOC-induced CPGE shows a twofold degeneracy, while the removal of the sixfold degeneracy is attributed to the asymmetrical optical absorption. Furthermore, the interfacial SOC-induced CPGE shows a weak dependence on the external gate voltage, which is totally different from the WSIA-related SOC. This result is consistent with the clarification that the interfacial asymmetry originates from the Fermi level pinning at the GaN NW sidewall surfaces, thus clearly illustrating the special distribution and gate dependences of the interfacial SOC, which is critical for the design of spintronic devices based on GaN NWs.