Fractional power-law behavior and its origin in iron-chalcogenide and ruthenate superconductors: Insights from first-principles calculations

TL;DR

This study uses first-principles calculations to reveal orbital-dependent fractional power-law behavior and incoherence in iron chalcogenides and ruthenates, linking these phenomena to Hund's coupling effects rather than quantum criticality.

Contribution

It identifies the origin of fractional power-law behavior and electronic incoherence in these materials through detailed first-principles analysis, highlighting Hund's coupling as a key factor.

Findings

Orbital-dependent fractional power-law behavior observed in FeTe and KxFe2-ySe2.

Electronic states become hidden at high temperatures and reemerge at low temperatures.

Anomalies are due to coexistence of orbital and spin fluctuations, not quantum criticality.

Abstract

We perform realistic first-principles calculations of iron chalcogenides and ruthenate based materials to identify experimental signatures of Hund's coupling induced correlations in these systems. We find that FeTe and K$_x$Fe$_{2-y}$Se$_2$ display unusual orbital dependent fractional powerlaw behavior in their quasiparticle self energy and optical conductivity, a phenomena first identified in SrRuO$_3$. Strong incoherence in the paramagnetic state of these materials results in electronic states hidden to angle-resolved photoemission spectroscopy which reemerge at low temperatures. We identify the effective low energy Hamiltonian describing these systems and show that these anomalies are not controlled by the proximity to a quantum critical point but result from coexistence of fast quantum mechanical orbital fluctuations and slow spin fluctuations.