Würzburg ToCoTronics Colloquium

In this talk, I will introduce light-driven scanning tunneling microscopy (STM) and discuss how it can be used to probe electronic and structural excitations and nonequilibrium processes at surfaces and in atomic-scale junctions. In particular, I will highlight the vast progress the field of ultrafast STM (USTM) has made in the last decade [1], and how excitation of an STM with femtosecond laser and/or THz pulses enables imaging with simultaneous angstrom spatial and ultrafast temporal resolution. I will introduce photon (quantum) driven and lightwave (field) driven tunneling as two distinct modes of USTM operation, and discuss different regimes of light-matter interaction and nonequilibrium tunneling phenomena in atomic-scale junctions. I will demonstrate that photon-driven
USTM using plasmonic junctions can be used to map coherent lattice vibrations with ~1 nm spatial resolution [2], providing complementary information to steady-state vibrational local probes such as tip-enhanced Raman spectroscopy (TERS). Moreover, I will present THz-lightwave-driven STM (THz-STM) [3] and discuss its application for probing the dynamics of photoexcited electrons [4] and collective excitations in strongly correlated materials [5]. I will show first results demonstrating ultrafast detection of the photoexcited coherent amplitude mode (AM) of the charge density wave (CDW) in 1T-TaS2 locally with THz-STM. I will discuss possible mechanisms by which USTM can track the dynamics of coherent phonons, hot carriers, and collective excitations via ultrafast modulation of the tunneling current. Finally, I will outline future directions for imaging the spatiotemporal evolution of quantum many-body states by USTM.

[1] M. Müller, Prog. Surf. Sci., in print (2023)
[2] S. Liu et al., Sci. Adv. 8, eabq5682 (2022)
[3] T. Cocker et al., Nat. Phot. 15, 558-569 (2021)
[4] N. Martín-Sabanés et al., ACS Nano 16, 9 (2022)
[5] L. E. Parra Lopéz, in preparation