SKM 2023 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 28: Unconventional Superconductors
TT 28.6: Invited Talk
Wednesday, March 29, 2023, 10:45–11:15, HSZ 103
Studying the Fulde-Ferrell-Larkin-Ovchinnikov order parameter in quasi-2D organic superconductors — •Tommy Kotte1, S. Molatta1, D. Opherden1, G. Koutroulakis2, S. E. Brown3, J. A. Schlueter4,5, H. Kühne1, G. Zwicknagl6, and J. Wosnitza1,7 — 1Hochfeld-Magnetlabor Dresden, HZDR — 2UC Santa Barbara, USA — 3UC Los Angeles, USA — 4NSF, Alexandria, USA — 5ANL, Argonne, USA — 6IMP, TU Braunschweig — 7IFMP, TU Dresden
The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state can emerge in superconductors for which the orbital critical field exceeds the Pauli limit. This unconventional superconducting state is characterized by a spatial modulation of the superconducting order parameter. Although evidence of the formation of an FFLO state has been found in various classes of materials, it is still theoretically debated and experimentally unexplored how the superconducting order parameter evolves within the FFLO phase. Here, we present two fundamental studies concerning this question in quasi-2D organic superconductors, which are well established to host an FFLO state: (i) By means of 13C NMR spectroscopy on β”-(ET)2SF5CH2CF2SO3, we were able to quantify the modulation amplitude of the spin polarization throughout the FFLO state. This quantity is related to the modulated superconducting gap, hence representing the order parameter. (ii) By means of angular-resolved specific-heat measurements on κ-(ET)2Cu(NCS)2, we furthermore show how the FFLO order parameter becomes unstable against orbital interactions, leading to a crossover from the FFLO into Abrikosov-like states of higher-order Landau levels.