Dresden 2017 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 21: Focus Session: Nematicity, Magnetism and Superconductivity in FeSe and Related Compounds
TT 21.1: Invited Talk
Tuesday, March 21, 2017, 09:30–10:00, HSZ 03
BCS-BEC Crossover, Preformed Pairs and Highly Spin-Polarized Superconducting Phase in FeSe — •Yuji Matsuda — Kyoto University, Kyoto, Japan
There is growing evidence that superconducting semimetal FeSe (Tc=8K) is deep in the crossover regime between weak coupling Bardeen-Cooper-Schrieffer (BCS) and strong-coupling Bose-Einstein-condensate (BEC) limits. Therefore FeSe offers a unique and fascinating platform to study the crossover physics. Here we discuss several unique features which may provide new insights into fundamental aspects of the crossover. First is the observation of giant superconducting fluctuations by far exceeding the standard Gaussian theory and a possible pseugogap formation above Tc. Second is the electronic structure. FeSe is a compensated semimetal, and hence it is essentially multiband superconductor, which makes the crossover physics in FeSe distinguished from that in ultracold atomic gases. Third concerns the fate of the superfluid when the spin populations are strongly imbalanced. In FeSe in the crossover regime, the Zeeman effect is especially effective in shrinking the Fermi volume associated with the spin minority. We show the emergence of a distinct field-induced superconducting phase, which has an unprecedentedly large spin-imbalance.