Berlin 2024 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 36: Superconductivity: Theory I

TT 36.7: Talk

Wednesday, March 20, 2024, 11:00–11:15, H 3005

Exceeding the Chandrasekhar-Clogston limit in flat-band superconductors: A multiband strong-coupling approach — •Kristian Maeland and Asle Sudbø — Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway

Hybrid systems of superconductors and magnets display promising applications in superconducting spintronics. This motivates a search for systems where superconductivity can survive larger in-plane critical magnetic fields than the conventional limit. The Chandrasekhar-Clogston (CC) limit applies to thin-film conventional superconductors with in-plane magnetic fields. For a magnetic field strength comparable to the superconducting gap, a spin-split normal state attains lower free energy than the superconducting state. A multiband superconductor with a flat band placed just below the Fermi surface has been shown to surpass the CC limit using weak-coupling theory. It is natural to anticipate corrections from strong-coupling theory in flat-band systems, owing to the large density of states of the flat bands. We derive Eliashberg equations and the free energy for a multiband superconductor in a magnetic field. First, we show that the CC limit can be exceeded by a small amount in one-band strong-coupling superconductors due to self-energy renormalization of the magnetic field. Next, we consider a two-band system with one flat band and find that the CC limit can be exceeded by a large amount also in strong-coupling theory, even when including hybridization between bands that intersect. [1] arXiv:2310.03082

Keywords: Strong-coupling superconductivity; Eliashberg theory; Chandrasekhar-Clogston limit; Phonon-mediated superconductivity; Superconducting spintronics