Imaging orbital-selective quasiparticles in the Hund’s metal state of FeSe

Abstract

Strong electronic correlations, emerging from the parent Mott insulator phase, are key to copper-based high-temperature superconductivity. By contrast, the parent phase of an iron-based high-temperature superconductor is never a correlated insulator. However, this distinction may be deceptive because Fe has five actived 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 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 appear on all detectable bands over a wide energy range. Further, the quasiparticle interference amplitudes reveal that [Formula: see text], consistent with earlier orbital-selective Cooper pairing studies. Thus, orbital-selective strong correlations dominate the parent state of iron-based high-temperature superconductivity in FeSe.

kz Selective Scattering within Quasiparticle Interference Measurements of FeSe

“…In the supplementary material, we present simulations including the quasiparticle weight factors suggested in Refs. [14]. We find that, although this approach does account for the general observation of highly two-fold symmetric QPI spectra and qualitatively captures some features, a more satisfactory agreement can be found within our approach, in which we keep all the orbitals coherent but implement a pocket-selective coherence.…”

“…The removal of states "by hand", makes this model highly phenomenological, however, within the energy region of ±50 meV, this approach quantitatively reproduces the experimental band dispersions measured by ARPES experiments on detwinned crystals [17][18][19]. The calculation of the local density of states (LDOS), N (r, ω), measured by QPI experiments, has been discussed extensively within the literature [14,26,27]. Here we employ the same T-matrix formalism [28], however, we extend the definition to include out-of-plane scattering vectors.…”

“…However, in our understanding, the QPI data does not support this interpretation; there is no band minimum observed above the Fermi level, and no low-q electron-like dispersions in the q x direction (Fig 3e). Another proposition is that the apparent absence of spectral weight on the second electron pocket is a manifestation of orbital-selective quasiparticle weights [14], since the phenomenological suppression of d xz and d xy weight would particularly affect this pocket. In the supplementary material, we present simulations including the quasiparticle weight factors suggested in Refs.…”

“…As we are assuming a point-like impurity, the impurity potential, V , is assumed to be a constant. In this report we set V = −100 meV, as suggested by tunnelling experiments on FeSe [14].…”

“…In this report we will show that the scattering dispersion of FeSe, measured by QPI [12][13][14], can be directly reproduced from a model that captures the "one-electron-pocket" FIG. 1.…”