Controlling Photocurrent Channels in Scanning Tunneling Microscopy

Benjamin Schröder, Ole Bunjes, Lara Wimmer, Katharina Kaiser, Georg A. Traeger, Thomas Kotzott, Claus Ropers, Martin Wenderoth
2020 New Journal of Physics  
We investigate photocurrents driven by femtosecond laser excitation of a (sub)-nanometer tunnel junction in an ultrahigh vacuum low-temperature scanning tunneling microscope (STM). The optically driven charge transfer is revealed by tip retraction curves showing a current contribution for exceptionally large tip-sample distances, evidencing a strongly reduced effective barrier height for photoexcited electrons at higher energies. Our measurements demonstrate that the magnitude of the
more » ... e of the photo-induced electron transport can be controlled by the laser power as well as the applied bias voltage. In contrast, the decay constant of the photocurrent is only weakly affected by these parameters. Stable STM operation with photoelectrons is demonstrated by acquiring constant current topographies. An effective nonequilibrium electron distribution as a consequence of multiphoton absorption is deduced by the analysis of the photocurrent using a one-dimensional potential barrier model.
doi:10.1088/1367-2630/ab74ac fatcat:nzxwbmr3nra3fiynmsdgu7mkr4