Imaging Orbital-selective Quasiparticles in the Hund's Metal State of FeSe
22 Jul 2018
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Kostin Andrey
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Sprau Peter O.
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Kreisel Andreas
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Chong Yi Xue
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Böhmer Anna E.
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Canfield Paul C.
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Hirschfeld Peter J.
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Andersen Brian M.
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Davis J. C. Séamus
Strong electronic correlations, emerging from the parent Mott insulator
phase, are key to copper-based high temperature superconductivity (HTS). By
contrast, the parent phase of iron-based HTS is never a correlated insulator...But this distinction may be deceptive because Fe has five active d-orbitals
while Cu has only one. In theory, such orbital multiplicity can generate a
Hund's Metal state, in which alignment of the Fe spins suppresses inter-orbital
fluctuations producing orbitally selective strong correlations. The spectral
weights $Z_m$ of quasiparticles associated with different Fe orbitals m should
then be radically different. Here we use quasiparticle scattering interference
resolved by orbital content to explore these predictions in FeSe. Signatures of
strong, orbitally selective differences of quasiparticle $Z_m$ appear on all
detectable bands over a wide energy range. Further, the quasiparticle
interference amplitudes reveal that $Z_{xy}<Z_{xz}<<Z_{yz}$, consistent with
earlier orbital-selective Cooper pairing studies. Thus, orbital-selective
strong correlations dominate the parent state of iron-based HTS in FeSe.(read more)