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Motion of electrons is at the heart of any chemical transformation, photo-induced charge or energy transfer process in molecules. Contemporary techniques in ultrafast science have the capability to generate and trace the consequences of this motion in real-time, but not in real-space. Scanning tunnelling microscopy (STM), on the other hand, can locally probe the valence electron density in molecules, but cannot provide by itself dynamical information at this ultrafast time scale. In my talk, I will show you how dynamics of coherent superposition of valence electron states generated by < 5 femtosecond long carrier-envelope-phase (CEP) stable laser pulses, can be locally probed with angstrom-scale spatial resolution and 300 attosecond temporal resolution simultaneously, at the single orbital-level with the help of an STM, defying the previously established fundamental space-time limits [1-4]. Electronic motion in molecules is usually coupled with atomic motion, especially in molecules undergoing photo-induced charge/energy transfer, structural or chemical transformation. In order to understand this coupling, we have recently realized femtosecond broadband coherent anti-Stokes Raman spectroscopy (CARS) in an STM and it has enabled tracking of coherent atomic motions in a single graphene nanoribbon with sub-angstrom scale spatial, meV energy and ~30 fs temporal resolution, simultaneously [5-6]. Time-resolved CARS implemented in an STM is the key to probing both electronic and atomic motion at the same time.
1. Garg et al. Nature 359-363, 538 (2016).
2. Gutzler, Garg et al. Nature Reviews Physics 3, 441-453 (2021).
3. Garg et al., Nature Photonics, 16, 196-202 (2022).
4. Garg and Kern. Science 367 (6476), 411-415 (2020).
5. Luo et al. Nano Letters 22 (13), 5100-5106 (2022).
6. Luo et al. Under Review (2022). arXiv:2210.02561
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