Evidence for an FFLO state with segmented vortices in the BCS-BEC-crossover superconductor FeSe

2019/11/19 by S. Kasahara, Y. Sato, S. Licciardello +10 · 1 citation
Physics and Astronomy · #cond-mat.supr-con #cond-mat.quant-gas #cond-mat.str-el

paper · pdf · doi:10.1103/physrevlett.124.107001

published as Phys. Rev. Lett. 124, 107001 (2020) · 6 pages, 4 figures

arxiv created 2019/11/19 · arxiv updated 2020/03/17

Abstract

We present resistivity and thermal-conductivity measurements of superconducting FeSe in intense magnetic fields up to 35 T applied parallel to the ab plane. At low temperatures, the upper critical field μ₀ H_c2^ab shows an anomalous upturn, while thermal conductivity exhibits a discontinuous jump at μ₀ H^∗≈ 24 T well below μ₀ H_c2^ab, indicating a first-order phase transition in the superconducting state. This demonstrates the emergence of a distinct field-induced superconducting phase. Moreover, the broad resistive transition at high temperatures abruptly becomes sharp upon entering the high-field phase, indicating a dramatic change of the magnetic-flux properties. We attribute the high-field phase to the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state, where the formation of planar nodes gives rise to a segmentation of the flux-line lattice. We point out that strongly orbital-dependent pairing as well as spin-orbit interactions, the multiband nature, and the extremely small Fermi energy are important for the formation of the FFLO state in FeSe.

Cited by

• Anisotropic dynamic excitations in a two-dimensional Fulde-Ferrell superfluid