Influence of Radio-frequency Voltage on Electron Spin Resonance Spectroscopy in Scanning Tunneling Microscopy^†

Over the last decade, the integration of scanning tunneling microscopy (STM) and electron spin resonance (ESR) spectroscopy has emerged as a powerful tool for measuring spin states of surface-adsorbed molecules. The radio-frequency voltage is a key physical quantity that influences STM-ESR spectra. However, the specific effect of radio-frequency voltage on the real-time electric current associated with STM-ESR signal remains unclear. In this work, we employ the hierarchical equations of motion method to simulate the STM-ESR spectra of a single spin-1/2 surface-adsorbed molecule and track the temporal evolution of the electric current, thereby elucidating how the radio-frequency voltage influences the features of STM-ESR spectra, the real-time electric current, and the characteristic frequencies conveyed by the electric current. These theoretical insights facilitate a deeper comprehension of experimental phenomena.