연사: Seokjin Bae from University of Illinois

일시: 2026년 9월 22일 2:00 – 3:00pm

장소: 연구협력관 B1 Jupiter 세미나룸

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

초록:  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.