Regensburg 2022 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 25: Focus Session: Atomic-Scale Characterization of Correlated Ground States in Epitaxial 2D Materials
O 25.5: Vortrag
Dienstag, 6. September 2022, 12:15–12:30, H2
Superconductivity of ultrathin crystalline Al films — •Werner M.J. van Weerdenburg1, Anand Kamlapure1, Niels P.E. van Mullekom1, Xiaochun Huang1, Manuel Steinbrecher1, Peter Krogstrup2, and Alexander A. Khajetoorians1 — 1Institute for Molecules and Materials, Radboud University Nijmegen, the Netherlands — 2Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
While bulk Al is one of the best known BCS superconductors (SC), it exhibits strange SC behavior in the thin film limit, e.g. a strong enhancement of the critical temperature Tc [1]. The transition from bulk to thin film can modulate the electronic structure and quasiparticle excitations, and the interface with the substrate becomes relevant [2]. Understanding the role of reduced dimensionality, screening and interface effects is important for SC quantum technology.
Here, we study epitaxially grown crystalline Al films on Si(111) as a function of film thickness. Using scanning tunneling microscopy / spectroscopy with temperatures down to 30 mK, we show a strong increase of both the SC gap size Δ and Tc for coverages between 4 and 35 monolayers. Remarkably, we find that Δ is threefold enhanced compared to the bulk value. We characterize the SC state of the thin films in (vector) magnetic field and find a new vortex structure.
[1] P.W Adams et al., Phys. Rev. B 95, 094520 (2017)
[2] A. Kamlapure et al., arXiv:2109.08498 (2021)