Moritz Frankerl
University of Regensburg, Institute for Theoretical Physics

Spin-orbit dynamics and Jahn-Teller effect in single molecule junctions

Scanning tunnelling microscopy (STM) is a firmly established tool to investigate molecular systems.
In the last decade it became possible to couple light waves to the nano-junction in order to combine angstrom spatial resolution of an STM with the sup-picosecond time resolution of THz pump-probe spectroscopy [1, 2].
In this talk, I will report on our theoretical investigations of a copper-phthalocyanine (CuPc) molecule in such a junction [3].
The spin-orbit interaction on the molecule’s metallic center is responsible for charge beatings as a function of the delay time between pump and probe pulses.
We describe these dynamics directly in the time domain with a generalized master equation approach.
In the second part of the talk, I will focus on the alternate-charging scanning tunneling microscopy (AC-STM).
In this set-up the use of thick salt layers decouples the molecule from the conducting substrate allowing to stabilize charges on the molecule[4].
The degenerate LUMOs of CuPc show a Jahn-Teller splitting upon charging and more surprisingly, the same LUMO gets occupied by both electrons upon double charging.
We show that the Jahn-Teller splitting for CuPc in gas phase is not sufficient to account for this behavior and propose an explanation in terms of a cooperation between molecule and substrate deformation.

[1] T. L. Cocker et al., Nature Photon 7, 620-625 (2013)
[2] T. L. Cocker et al., Nature 539, 263-267 (2016)
[3] M. Frankerl and A. Donarini, PRB 103, 085420 (2021)
[4] L. Patera et al., Nature 566, 245-248 (2019)