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O: Fachverband Oberflächenphysik

O 3: Mini-Symposium: Ultrafast surface dynamics at the space-time limit I

O 3.5: Invited Talk

Monday, March 1, 2021, 12:00–12:30, R1

Atomic-resolution imaging of THz-driven dynamics on charge-ordered surfaces — •Sebastian Loth — Universität Stuttgart, Institut für Funktionelle Materie und Quantentechnologien, 70569 Stuttgart — Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart

Charge order in correlated-electron materials is intimately linked to fluctuations of charge density that occur at nanometer length scales and at ultrafast speed. Such localized fluctuations are not a simple perturbation but can be the determining factor for the dynamics of phase transitions and the macroscopic response of the electron system. While these fluctuations often remain hidden to ensemble-averaged measurements, the combination of ultrafast THz spectroscopy and scanning tunneling microscopy can both locally excite and probe dynamics with atomic spatial and femtosecond temporal resolution [1]. For the quasi two-dimensional charge density wave state in niobium diselenide we find that the tip-enhanced electric field of the THz pulses excites the sample directly by driving a strong in-plane displacement current in the surface. This leads to a distortion of the charge-density wave in the vicinity of atomic pinning sites that relaxes by emitting a complex pattern of amplitude and phase excitations rather than a uniform collective response. Resolving these fluctuations in real space at the scale of individual impurities provides a new route to unraveling the electronic dynamics of disordered correlated materials.

[1] T. L. Cocker et al., Nature Photon. 7, 620 (2013). & T. L. Cocker et al., Nature 539, 263 (2016).