Izabela Bialo (AGH University of Science and Technology, Krakow & TU Wien)

Pulsed-field X-ray absorption spectroscopy study in High-Tc superconductors

The phenomenon of high-transition-temperature (high-Tc) superconductivity is one of the most exciting, thoroughly investigated, yet still unresolved problems. A major difficulty in understanding high Tc systems is the complexity of the materials, the presence of strong electron-electron interactions, and their rich phase diagrams. The delicate balance among a number of coexisting phases makes it hard to identify the principal interactions. High magnetic fields play an important role in studying the high-Tc phenomenon, because such fields suppress the superconducting state and enable the exploration of competing states in the normal state (e.g., in the absence of superconductivity). In this work we used X-ray absorption spectroscopy at the Cu K-edge to study the origin of the magnetic field induced three-dimensional charge density wave order in the cuprate superconductors. While changes in the absorption spectra were observed upon applying magnetic field in orthorhombic YBCO, no impact of the magnetic field on the absorption spectra was detected in the orthorhombic cuprates. The onset of the field induced changes in the spectra is consistent with the value of the magnetic field above which the three-dimensional charge correlations were detected via X-ray diffraction [1,2]. Furthermore, the energy range of the spectra where the changes were observed corresponds to the Cu-states within the unidirectional Cu-O chains, characteristic to YBCO. We conclude, that the magnetic field induced charge correlations are specific to YBCO, due to the existence of the Cu-O chains, and not generic to the cuprate superconductors.

References:
[1] S. Gerber et al., Science
[2] J. Chang et al., Nature Comm. 2016