Quantum matter in high magnetic fields

Abstract:

Isoelectronic substitution is an ideal tuning parameter to alter electronic states and correlations in iron-based superconductors. As this substitution takes place outside the conducting Fe planes, the electronic behaviour is less affected by the impurity scattering experimentally and relevant key electronic parameters can be accessed. In this short review, I present the experimental progress made in understanding the electronic behaviour of the nematic electronic superconductors, FeSe1-xSx. A direct signature of the nematic electronic state is in-plane anisotropic distortion of the Fermi surface triggered by orbital ordering effects and electronic interactions that result in multi-band shifts detected by ARPES. Upon sulphur substitution, the electronic correlations and the Fermi velocities decrease in the tetragonal phase. Quantum oscillations are observed for the whole series in ultra-high magnetic fields and show a complex spectra due to the presence of many small orbits. Effective masses associated to the largest orbit display non-divergent behaviour at the nematic end point (x~0.175(5)), as opposed to critical spin-fluctuations in other iron pnictides. Magnetotransport behaviour has a strong deviation from the Fermi liquid behaviour and linear T resistivity is detected at low temperatures inside the nematic phase, where scattering from low energy spin-fluctuations are likely to be present. The superconductivity is not enhanced in FeSe1-xSx and there are no divergent electronic correlations at the nematic end point. These manifestations indicate a strong coupling with the lattice in FeSe1-xSx and a pairing mechanism likely promoted by spin fluctuations.

Abstract:

The data are part of the publication "Signatures of a Quantum Griffiths Phase close to an Electronic Nematic Quantum Phase Transition" https://arxiv.org/abs/2103.07991 to appear in Physical Review Letters. The magnetotransport data were collected at the National High Magnetic Field Laboratory in Tallahassee up to 45T as well as in Oxford up to 16T. The raw data which are part of the figures are provided as .DAT ASCII files. Figure 1 contains an image made with Mathematica code.

Abstract:

These data are part of the publication entitled "Strain-tuning of nematicity and superconductivity in single crystals of FeSe" to appear in Physical Review B (also on archive arXiv:2102.11984, https://arxiv.org/abs/2102.11984). The data collected are resistivity data measured as a function of temperature of FeSe under applied uniaxial strain. Measurements were also collected at fixed temperature by varying the applied strain. Studies were also perfomed in magnetic fields. Each data file is related to the different figures reported in the manuscript.