Quantum Criticality in the 122 Iron Pnictide Superconductors Emerging from Orbital-Selective Mottness

TL;DR

This study combines experimental measurements and theoretical modeling to reveal an orbital-selective Mott transition and electronic nematic order as key factors in the unconventional superconductivity of 122 iron pnictides.

Contribution

It provides new evidence linking orbital-selective Mottness and nematic order to the pairing mechanism in iron-based superconductors.

Findings

Identification of an orbital-selective Mott transition in Sr(Fe,Co)2As2

Observation of electronic nematic order near optimal doping

Evidence for a quantum-critical point driving superconductivity

Abstract

The twin issues of the nature of the normal state and competing order(s) in the iron arsenides are central to understanding their unconventional, high-Tc superconductivity. We use a combination of transport anisotropy measurements on detwinned Sr(Fe(1-x)Co(x))2As2 single crystals and local density approximation plus dynamical mean field theory (LDA + DMFT) calculations to revisit these issues. The peculiar resistivity anisotropy and its evolution with x are naturally interpreted in terms of an underlying orbital-selective Mott transition (OSMT) that gaps out the dxz or dyz states. Further, we use a Landau-Ginzburg approach using LDA + DMFT input to rationalize a wide range of anomalies seen up to optimal doping, providing strong evidence for secondary electronic nematic order. These findings suggest that strong dynamical fluctuations linked to a marginal quantum-critical point associated with this OSMT and a secondary electronic nematic order constitute an intrinsically electronic pairing mechanism for superconductivity in Fe arsenides.