Optical Stark Effect of a Single Defect on TiO2(110) Surface

TL;DR

This study demonstrates the optical Stark effect at a single atomic defect on TiO2(110) surface using photo-assisted STM, revealing how laser coupling influences defect states at the atomic scale.

Contribution

It provides the first detailed observation of optical Stark effect on single atomic defects on TiO2(110) surface with a novel explanation involving tip-enhancement and dipole moments.

Findings

Mid-gap state shifts with laser power

Peak broadening observed in spectra

Optical Stark effect explained by Autler-Townes formula

Abstract

Probing optical Stark effect at the single-molecule or atomic scale is crucial for understanding many photo-induced chemical and physical processes on surfaces. Here we report a study about optical Stark effect of single atomic defects on TiO2(110) surface with photo-assisted scanning tunneling spectroscopy. When a laser is coupled into the tunneling junction, the mid-gap state of OH-O2 defects changes remarkably in the differential conductance spectra. As laser power gradually increases, the energy of the mid-gap state shifts away from the Fermi level with increase in intensity and broadening of peak width. The observation can be explained as optical Stark effect with the Autler-Townes formula. This large optical Stark effect is due to the tip-enhancement and the strong dipole moment in the transient charged state during electron tunneling. Our study provides new aspects in exploring electron-photon interactions at the microscopic scale.