Quantum matter in high magnetic fields

Abstract:

FeSe is a fascinating superconducting material at the frontier of research in condensed matter physics. Here we provide an overview on the current understanding of the electronic structure of FeSe, focusing in particular on its low energy electronic structure as determined from angular resolved photoemission spectroscopy, quantum oscillations and magnetotransport measurements of single crystal samples. We discuss the unique place of FeSe amongst iron-based superconductors, being a multi-band system exhibiting strong orbitally-dependent electronic correlations and unusually small Fermi surfaces, prone to different electronic instabilities. We pay particular attention to the evolution of the electronic structure which accompanies the tetragonal-orthorhombic structural distortion of the lattice around 90 K, which stabilizes a unique nematic electronic state. Finally, we discuss how the multi-band multi-orbital nematic electronic structure has an impact on the understanding of the superconductivity, and show that the tunability of the nematic state with chemical and physical pressure will help to disentangle the role of different competing interactions relevant for enhancing superconductivity.

Abstract:

We report magnetotransport studies in thin (<100nm) exfoliated films of Cu_xBi₂Se₃ and we detect an unusual electronic transition at low temperatures. Bulk crystals show weak superconductivity with T_c∽3.5K and a possible electronic phase transition around 200K. Following exfoliation, superconductivity is supressed and a strongly temperature dependent multi-band conductivity is observed for T<30K. This transition between competing conducting channels may be enhanced due to the presence of electronic ordering, and could be affected by the presence of an effective internal stress due to Cu intercalation. By fitting to the weak antilocalisation conductivity correction at low magnetic fields we confirm that the low temperature regime maintains a quantum phase coherence length L_φ > 100nm indicating the presence of topologically protected surface states.

Abstract:

These data were created by recording the transport behaviour on thin flakes devices at low temperatures and in magnetic field. These are all DAT files easily readable

Abstract:

These are the Raw data used to generate the figures related to the publication: "Evolution of the Fermi surface of the nematic superconductors FeSe1-xSx" by A. I. Coldea et al.

Abstract:

These data make up the figures of the paper with the same name to be published in Physical Review Materials. The data are raw .DAT file created mainly by measuring magnetization in magnetic field at different temperatures and analysing the raw data, as described in the paper.