Berlin 2015 – wissenschaftliches Programm
TT 66.10: Vortrag
Mittwoch, 18. März 2015, 17:45–18:00, H 2053
Superconducting phase transition in STM tips — •Matthias Eltschka1, Berthold Jäck1, Maximilian Assig1, Markus Etzkorn1, Christian R. Ast1, and Klaus Kern1, 2 — 1Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany — 2Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
The superconducting properties of systems with dimensions comparable to the London penetration depth considerably differ from macroscopic systems. We have studied the superconducting phase transition of vanadium STM tips in external magnetic fields. Employing Maki’s theory we extract the superconducting parameters such as the gap or the Zeeman splitting from differential conductance spectra. While the Zeeman splitting follows the theoretical description of a system with s=1/2 and g=2, the superconducting gaps as well as the critical fields depend on the specific tip. For a better understanding of the experimental results, we solve a one dimensional Usadel equation modeling the superconducting tip as a cone with the opening angle α in an external magnetic field. We find that only a small region at the apex of the tip is superconducting in high magnetic fields and that the order of the phase transition is directly determined by α. Further, the spectral broadening increases with α indicating an intrinsic broadening mechanism due to the conical shape of the tip. Comparing these calculations to our experimental results reveals the order of the superconducting phase transition of the STM tips.