Quadrupolar charge dynamics in the nonmagnetic FeSe 1− x S x superconductors
- 12 May 2021
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences of the United States of America
- Vol. 118 (20)
- https://doi.org/10.1073/pnas.2020585118
Abstract
We use polarization-resolved electronic Raman spectroscopy to study quadrupolar charge dynamics in a nonmagnetic superconductor. We observe two types of long-wavelength symmetry excitations: 1) a low-energy quasi-elastic scattering peak (QEP) and 2) a broad electronic continuum with a maximum at 55 meV. Below the tetragonal-to-orthorhombic structural transition at , a pseudogap suppression with temperature dependence reminiscent of the nematic order parameter develops in the symmetry spectra of the electronic excitation continuum. The QEP exhibits critical enhancement upon cooling toward . The intensity of the QEP grows with increasing sulfur concentration x and maximizes near critical concentration , while the pseudogap size decreases with the suppression of . We interpret the development of the pseudogap in the quadrupole scattering channel as a manifestation of transition from the non-Fermi liquid regime, dominated by strong Pomeranchuk-like fluctuations giving rise to intense electronic continuum of excitations in the fourfold symmetric high-temperature phase, to the Fermi liquid regime in the broken-symmetry nematic phase where the quadrupole fluctuations are suppressed.
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