Evolution of the Fermi surface of the nematic superconductors FeSe_1-xS_x

I will present the evolution of the Fermi surfaces and electronic interactions across the nematic phase transition in single crystals of FeSe_1-xS_x using Shubnikov-de Haas oscillations in high magnetic fields up to 45 tesla in the low temperature regime. The unusually small and strongly elongated Fermi surface of FeSe increases monotonically with chemical pressure, x, due to the suppression of the in-plane anisotropy except for the smallest orbit which suffers a Lifshitz-like transition once nematicity disappears. Even outside the nematic phase the Fermi surface continues to increase, in stark contrast to the reconstructed Fermi surface detected in FeSe under applied external pressure. I will present the unusual signatures of orbital-dependent quasiparticle mass renormalization suppressed for those orbits with dominant d_xz/yz character, but unusually enhanced for those orbits with dominant dxy character. The lack of enhanced superconductivity outside the nematic phase in FeSe_1-xS_x suggest that nematicity may not play the essential role in enhancing Tc in these systems.