Amalia Coldea

Abstract:

This data set accompanies the publication entitled "Anisotropic magnetic interactions in a candidate Kitaev spin liquid close to a metal-insulator transition" posted on the archive (https://arxiv.org/abs/2407.15657) and also to appear in Communication Physics. These data were generated by firstly performing X-ray diffraction on single crystals of RuI3. The torque experiments were performed using piezocantilevers and a single axis rotator in a 16T PPMS cryostat at different temperatures. The detailed measurements were performed for three different plans of rotations. The data were analyzed using Fourier decomposition of the contribution to the torque signal as well as direct fitting using an empirical expression described in the text. The experimental data are compared with theoretical simulation using parameters described in the text.

Abstract:

This data set corresponds to the generated data for the publication entitled with the same name to appear in npj Quantum Materials in 2024. The data were collected while measuring resistivity in high magnetic fields and under applied pressure for a novel iron-based superconductor, FeSe1-xSx (x~0.18). Most of the data are ASCII files related to the figures provided (often (x,y) format).

Abstract:

Iron-chalcogenide superconductors display rich phenomena caused by orbital-dependent band shifts and electronic correlations. Additionally, they are potential candidates for topological superconductivity due to the band inversion between the Fe d bands and the chalcogen p_z band. Here we present a detailed study of the electronic structure of the nematic superconductors FeSe_1−xTe_x (0 < x < 0.4) using angle-resolved photoemission spectroscopy to understand the role of orbital-dependent band shifts, electronic correlations and the chalcogen band. We assess the changes in the effective masses using a three-band low energy model, and the band renormalization via comparison with DFT band structure calculations. The effective masses decrease for all three-hole bands inside the nematic phase, followed by a strong increase for the band with d_xy orbital character. Interestingly, this nearly-flat d_xy band becomes more correlated as it shifts towards the Fermi level with increasing Te concentrations and as the second superconducting dome emerges. Our findings suggests that the d_xy hole band, which is very sensitive to the chalcogen height, could be involved in promoting an additional pairing channel and increasing the density of states to stabilize the second superconducting dome in FeSe_1−xTe_x. This simultaneous shift of the d_xy hole band and enhanced superconductivity is in contrast with FeSe_1−xS_x.

Abstract:

The upper critical field of multi-band superconductors can be an essential quantity to unravel the nature of superconducting pairing and its interplay with the electronic structure. Here we experimentally map out the complete upper critical field phase diagram of FeSe for different magnetic field orientations at temperatures down to 0.3 K using both resistivity and torque measurements. The temperature dependence of the upper critical field reflects that of a multi-band superconductor and requires a two-band description in the clean limit with band coupling parameters favouring interband over intraband interactions. Despite the relatively small Maki parameter in FeSe of α ∼ 1.6, the multi-band description of the upper critical field is consistent with the stabilization of a FFLO state below T /Tc ∼ 0.3. We find that the anomalous behaviour of the upper critical field is linked to a departure from the single-band picture, and FeSe provides a clear example where multi-band effects and the strong anisotropy of the superconducting gap need to be taken into account.