Regensburg 2022 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 3: Superconductivity: Properties and Electronic Structure

TT 3.1: Talk

Monday, September 5, 2022, 09:30–09:45, H23

Is lead really a prototypical type I superconductor? New results on the phase diagram at ultra-low temperatures — Thomas Gozlinski, Qili Li, Rolf Heid, Jörg Schmalian, and •Wulf Wulfhekel — Karlsruhe Institute of Technology

Superconductors are classified by their behavior in a magnetic field into type I, which transitions from a superconducting Meissner to a normal state at the critical field and type II, which have an additional Shubnikov phase consisting of magnetic vortices with one magnetic flux quantum, each. For type I superconductors of finite lateral dimensions, the transition to the normal state is, however, known to occur locally in form of domains in the so-called intermediate Landau state. Basis for this classification are thermodynamic considerations near the critical temperature and a single band description of superconductivity. Although bulk lead (Pb) is classified as a prototypical type I superconductor, we surprisingly observe single and multi-flux quanta vortices in the intermediate state at temperatures far below the critical temperature using a 25 mK scanning tunneling microscope hand in hand with a complex superconducting behaviour of the two distinct Fermi surfaces of Pb. By probing the quasiparticle local density of states (LDOS) inside the vortices and comparison with quasi-classical simulations based on DFT band-structure calculations, we identify the Caroli-de-Gennes-Matricon states of the two superconducting bands of Pb and are consequently able to determine their winding number.