Nanoscale variations in the Rashba parameter of BiTeI*

BiTeI is a polar semiconductor with a strong spin-orbit coupling (SOC), which results in a large Rashba spin splitting. Due to a potential impact on spintronics and magnetoelectrics, it is essential to understand the behavior of single impurities in this material. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we imaged ring-like charging states of single-atom defects on the iodine surface of BiTeI. By density functional theory (DFT) calculation, we identified the three types of defects that induce the charge rings. We use the bias dependence of the ring radius as a local probe for surface charge density. Remarkably, we correlate the defect-quantified local charge density with the local Rashba energy of spin band splitting. Our results help understand the impact of a single defect on Rashba effect, which could play a role in making spintronic devices.