Quantum matter in high magnetic fields

Abstract:

Understanding superconductivity requires detailed knowledge of the normal electronic state from which it emerges. A nematic electronic state that breaks the rotational symmetry of the lattice can potentially promote unique scattering relevant for superconductivity. Here, we investigate the normal transport of superconducting FeSe$_{1-x}$S$_x$ across a nematic phase transition using high magnetic fields up to 69 T to establish the temperature and field-dependencies. We find that the nematic state is an anomalous non-Fermi liquid, dominated by a linear resistivity at low temperatures that can transform into a Fermi liquid, depending on the composition $x$ and the impurity level. Near the nematic end point, we find an extended temperature regime with $T^{1.5}$ resistivity. The transverse magnetoresistance inside the nematic phase has as a $H^{1.55}$ dependence over a large magnetic field range and it displays an unusual peak at low temperatures inside the nematic phase. Our study reveals anomalous transport inside the nematic phase, driven by the subtle interplay between the changes in the electronic structure of a multi-band system and the unusual scattering processes affected by large magnetic fields and disorder

Abstract:

We demonstrate the capability of embedded mean-field theory (EMFT) within the linear-scaling density-functional-theory code ONETEP, which enables DFT-in-DFT quantum embedding calculations on systems containing thousands of atoms at a fraction of the cost of a full calculation. We perform simulations on a wide range of systems from molecules to complex nanostructures to demonstrate the performance of our implementation with respect to accuracy and efficiency. This work paves the way for the application of this class of quantum embedding method to large-scale systems that are beyond the reach of existing implementations.

Abstract:

These data are raw data as part of the manuscript: "Anomalous high-magnetic field electronic state of the nematic superconductors FeSe1−xSx" (arXiv:1904.02522) https://arxiv.org/abs/1904.02522. The manuscript will be published as an Article in Physical Review Research 2020. The magnetotransport data were collected using high magnetic fields with Helium 3 cryostats either in Nijmegen up to 38T , Tallahahassee up to 45T and pulsed fields close to 65T in Toulouse. The data were collected using lock-in amplifiers. The data here are part of the figures presented in the manuscript were detailed figure captions are provided.

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 Oxford and the thin flakes were preparated at the University of Bath. The magnetotransport data were mainly funded by the Oxford Centre for Applied Superconductivity (CFAS) at Oxford 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 Oxford 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.