Investigating Ultrafast Electron and Phonon Dynamics at the Atomic Scale

Electrons, phonons, and their mutual interactions are crucial for the complex phenomena in strongly correlated materials. In this talk, I will show that electron and phonon dynamics can be investigated at the atomic scale by combining THz pump-probe spectroscopy and a scanning tunneling microscope (STM) [1,2]. THz pulses induce strong electric fields and voltage transients in the tunnel junction of the STM. This can produce femtosecond Coulomb forces in the STM junction that launch coherent acoustic phonon wavepackets into a sample resulting in transient lattice displacement at the surface [1]. The intense THz field can also accelerate the electrons on the sample surface and thus modulate the surface's charge density. The THz-induced voltage transients cause electron tunneling making them ideal to not only excite but also detect the surface ultrafast lattice and charge density dynamics locally using pump-probe spectroscopy methods [2]. We found that THz excitation enables acoustic phonon generations, charge density wave propagations, and electron delocalization in a Mott insulator. These results show the possibility to coherently control phonons, electron motions, and phase transitions in correlated materials.

[1] S. Sheng, A. Oeter, M. Abdo, K. Lichtenberg, M. Hentschel, S. Loth, Phys. Rev. Lett. 129, 043001 (2022).
[2] M. Abdo, S. Sheng, S. Rolf-Pissarczyk, L. Arnhold, J. A. J. Burgess, M. Isobe, L. Malavolti, S. Loth, ACS Photonics. 8, 702–708 (2021).