Probing light–matter interaction at the atomic scale with ultrafast scanningtunneling microscopy

Speaker: Seokjin Bae

Affiliation: University of Illinois

Abstract: Light–matterinteraction is a rapidly emerging frontier across quantum materials, revealingexotic phenomena that cannot be accessed at equilibrium and providing newcontrol knobs over quantum phases such as light-induced superconductivity andmagnetism, Floquet topological phases, and photoinduced chiral order. Despitethese advances, most studies have relied on macroscopic probes, leaving the microscopicunderstanding largely unexplored. To fill this gap, we have developed ultrafastscanning tunneling microscopy (ultrafast STM). In this talk, I will introducethis technique and its applications to materials with charge density wave (CDW)order and boundary modes from non-trivial topology.

In Part I, I willdiscuss symmetry control with light in a kagome metal RbV₃Sb₅. We show thatpolarization-controlled ultrafast optical excitation can switch the directionof mirror-symmetry breaking in the CDW state via light-induced directionalstrain, providing a real-space visualization of in situ optical manipulation of symmetry breaking on demand. In PartII, I will discuss edge photocurrent in a topological crystalline insulator(Pb,Sn)Se. Spatial maps of the transient tunneling current at the Dirac pointshow an enhanced photocurrent localized at atomic step edges that decays within 1 ps originated from the bulk-to-boundary carrier diffusion,demonstrating simultaneous atomic and femtosecond resolution of our ultrafastSTM.