Electronic Origin of Tc in Bulk and Monolayer FeSe

Swagata Acharya, Dimitar Pashov, Francois Jamet, Mark van Schilfgaarde

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9 Scopus Citations

Abstract

FeSe is classed as a Hund’s metal, with a multiplicity of d bands near the Fermi level. Correlations in Hund’s metals mostly originate from the exchange parameter J, which can drive a strong orbital selectivity in the correlations. The Fe-chalcogens are the most strongly correlated of the Fe-based superconductors, with dxy the most correlated orbital. Yet little is understood whether and how such correlations directly affect the superconducting instability in Hund’s systems. By applying a recently developed ab initio theory, we show explicitly the connections between correlations in dxy and the superconducting critical temperature Tc. Starting from the ab initio results as a reference, we consider various kinds of excursions in parameter space around the reference to determine what controls Tc. We show small excursions in J can cause colossal changes in Tc. Additionally we consider changes in hopping by varying the Fe-Se bond length in bulk, in the free standing monolayer M-FeSe, and M-FeSe on a SrTiO3 substrate (M-FeSe/STO). The twin conditions of proximity of the dxy state to the Fermi energy, and the strength of J emerge as the primary criteria for incoherent spectral response and enhanced single-and two-particle scattering that in turn controls Tc. Using constrained RPA, we show further that FeSe in monolayer form (M-FeSe) provides a natural mechanism to enhance J. We explain why M-FeSe/STO has a high Tc, whereas M-FeSe in isolation should not. Our study opens a paradigm for a unified understanding what controls Tc in bulk, layers, and interfaces of Hund’s metals by hole pocket and electron screening cloud engineering.

Original languageAmerican English
Article number169
Pages (from-to)1-16
Number of pages16
JournalSymmetry
Volume13
Issue number2
DOIs
StatePublished - 2021

Bibliographical note

Publisher Copyright:
Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

NREL Publication Number

  • NREL/JA-5F00-79447

Keywords

  • Hund’s metals
  • Spin susceptibilities
  • Unconventional superconductivity
  • Vertex functions

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