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O: Fachverband Oberflächenphysik

O 79: Electronic Structure of Surfaces: Spectroscopy, Surface States I

O 79.1: Hauptvortrag

Mittwoch, 22. März 2017, 15:00–15:30, WIL C307

Sensing the Quantum Limit in Scanning Tunneling Spectroscopy: From the Josephson Effect to Quantum Tunneling — •Christian R. Ast — Max-Planck-Institut für Festkörperforschung, Stuttgart

The tunneling current in scanning tunneling spectroscopy (STS) is typically and often implicitly modeled by a continuous and homogeneous charge flow. If the charging energy of a single-charge quantum sufficiently exceeds the thermal energy, however, the granularity of the current emerges. In this quantum limit, the capacitance of the tunnel junction mediates an interaction of the tunneling electrons with the surrounding electromagnetic environment and becomes a source of noise itself, which cannot be neglected in STS. Using a scanning tunneling microscope operating at 15 mK, we show that we operate in this quantum limit, which determines the ultimate energy resolution in STS. A theoretical description requires quantum electrodynamics to be included resulting in the P(E)-theory, which describes the probability for a tunneling electron to exchange energy with the environment. I will discuss this effect using a superconducting aluminium tip and a superconducting aluminium sample, where it is most pronounced. These considerations will be most important also at higher temperatures for extremely sharp spectral features, such as superconducting gaps, sharp Kondo peaks or Yu-Shiba-Rusinov states.