Electronic Origin of Tc in Bulk and Monolayer FeSe

Symmetry

Dimitar Pashov¹  Swagata Acharya¹  Francois Jamet¹  Mark van Schilfgaarde¹ 

[1] King’s College London, Theory and Simulation of Condensed Matter, The Strand, London WC2R 2LS, UK;

关键词: unconventional superconductivity;    spin susceptibilities;    vertex functions;    hund’s metals;   

DOI  :  10.3390/sym13020169

来源: DOAJ

【 摘 要 】

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 $d_{xy}$ 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 $d_{xy}$ and the superconducting critical temperature $T_c$. 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 $T_c$. We show small excursions in J can cause colossal changes in $T_c$. 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 SrTiO${}_3$ substrate (M-FeSe/STO). The twin conditions of proximity of the $d_{xy}$ 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 $T_c$. 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 $T_c$, whereas M-FeSe in isolation should not. Our study opens a paradigm for a unified understanding what controls $T_c$ in bulk, layers, and interfaces of Hund’s metals by hole pocket and electron screening cloud engineering.

【 授权许可】

Unknown