Unconventional Mott Transition in KxFe2-ySe2

TL;DR

This paper uses advanced computational methods to show that KxFe2-ySe2 is a doped Mott insulator, revealing a new type of insulator and explaining the emergence of superconductivity.

Contribution

It demonstrates that KxFe2-ySe2 is a Mott-Kondo insulator and that doping induces a Mott transition, providing a realistic scenario for superconductivity.

Findings

KFe1.6Se2 is a Mott-Kondo insulator.

Electron doping causes a Mott transition to a non-Fermi liquid metal.

Superconductivity likely emerges from a doped Mott insulator.

Abstract

Whether the newly discovered KxFe2-ySe2 systems are doped Mott or band insulators is key to how superconductivity emerges at lower temperature. With extant theoretical studies supporting conflicting scenarios, a more realistic approach is urgently called for. Here, we use LDA+DMFT to study this issue in KxFe2-ySe2. We find that the undoped KFe1.6Se2 system is a new kind of Mott-Kondo insulator (MKI). Electron doping this MKI drives a Mott transition to an orbital-selective non-Fermi liquid metal. Good agreement with spectral and transport responses supports our view, implying that superconductivity arises from a doped Mott insulator, as in the high-Tc cuprates.