Dresden 2026 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 85: Superconductivity: Yu-Shiba-Rusinov and Andreev Physics

TT 85.7: Talk

Thursday, March 12, 2026, 16:45–17:00, CHE/0089

Local Observation of Andreev Billiards in an In-Plane Magnetic Field — •Jens Brede, Adrian Greichgauer, and Yoichi Ando — University of Cologne

Quasiparticles in a normal metal can be confined by a surrounding superconductor through Andreev reflection at the N/S interface. For subgap energies, electrons are retroreflected as holes that retrace their paths, forming closed semiclassical trajectories. When their accumulated phase reaches 2π, these trajectories create Andreev bound states (ABS), observed as subgap features in the local density of states (LDOS). We probe these ABS using STM at 400 mK in the two-dimensional electron gas of the Cu(111) surface state, confined to quasi-rectangular islands by superconducting Nb. We observe a hard superconducting gap and, with increasing in-plane magnetic field, nearly periodic LDOS gap closings. The period scales roughly linearly with the island dimension perpendicular to the field direction. A simple model that incorporates the vector potential into the semiclassical trajectories qualitatively reproduces the experimental behavior.

Keywords: Andreev bound states; Scanning tunneling microscopy (STM); Superconductivity