The anomalous high magnetic field electronic state of the nematic iron-based superconductor FeSe_1-xS_x

Superconductivity is closely linked to the electronic states from which it emerges. Here we investigate the normal electronic state of the nematic superconductor FeSe_1-xS_x using magneto-transport and Hall Effect studies in magnetic fields up to 35 T (Nijmegen) and 70 T (Toulouse) over a large temperature range. Inside the nematic phase we find anomalous magneto-resistivity behaviour in very high magnetic fields, well above the upper critical field. The behaviour changes outside the nematic phase, where we show that at low temperatures Fermi-liquid behaviour is recovered. We account for the multiband structure and trace the carrier densities and motilities across the nematic phase transition. We also investigate the regime of superconducting fluctuations, which is expected to varying significantly in this isoelectronic series. We will discuss our results in relation to both Fermi liquid and non-Fermi liquid behaviour, and superconducting fluctuations.