91̽»¨

Abstract:

These data are part of the manuscript "Suppression of superconductivity and enhanced critical field anisotropy in thin flakes of FeSe" on https://arxiv.org/abs/1907.13174 which will appear in npj Quantum Materials 2020. The data are magnetotransport data on FeSe thin flakes. These data were mainly generated using a 16T PPMS in 91̽»¨ and the thin flakes were preparated at the University of Bath. The magnetotransport data were mainly funded by the 91̽»¨ Centre for Applied Superconductivity (CFAS) at 91̽»¨ University (www.cfas.ox.ac.uk).

Abstract:

These data are part of the manuscript (arXiv:2003.02888) entitled: "Competing pairing interactions responsible for the large upper critical field in a stoichiometric iron-based superconductor, CaKFe4As4". The data represent resistivity data collected at low temperatures and in magnetic fields up 16T using a superconducting magnet in 91̽»¨ as well as in pulsed fields up to 80T at the LNCMI in Toulouse, France. The measurements were performed between 2K and 300K either at constant temperature and varying the magnetic field or keeping the field constant and varying the temperature.

Abstract:

The nematic electronic state and its associated critical fluctuations have emerged as a potential candidate for the superconducting pairing in various unconventional superconductors. However, in most materials their coexistence with magnetically ordered phases poses a significant challenge in determining their importance. Here, by combining chemical and hydrostatic physical pressure in FeSe0.89S0.11, we access a nematic quantum phase transition isolated from any other competing magnetic phases. From quantum oscillations in high magnetic fields, we trace the evolution of the Fermi surface and electronic correlations as a function of applied pressure and detect a Lifshitz transition that separates two distinct superconducting regions. One emerges from the nematic phase with a small Fermi surface and strong electronic correlations, while the other one has a large Fermi surface and weak correlations that promotes nesting and stabilization of a magnetically ordered phase at high pressures. The absence of mass divergence at the nematic quantum phase transition suggests that the nematic fluctuations could be quenched by the strong coupling to the lattice or local strain effects. A direct consequence is the weakening of superconductivity at the nematic quantum phase transition in the absence of magnetically driven fluctuations.