Non-Fermi Liquid due to Orbital Fluctuations in Iron Pnictide Superconductors

TL;DR

This paper demonstrates that orbital fluctuations near a structural quantum critical point induce non-Fermi liquid behavior in iron-pnictide superconductors, explaining experimental tunneling observations and emphasizing the role of quantum criticality.

Contribution

It reveals how orbital fluctuations lead to non-Fermi liquid behavior in iron-pnictides, highlighting the significance of quantum criticality in their normal state properties.

Findings

Overdamped collective modes develop at low frequency in specific orbital channels.

Approaching the structural phase transition causes these modes to soften and gain spectral weight.

Non-Fermi liquid behavior characterized by $ ext{Im} ext{SelfEnergy} \, \sim \omega^\lambda$ is observed near the critical point.

Abstract

We study the influence of quantum fluctuations on the electron self energy in the normal state of iron-pnictide superconductors using a five orbital tight binding model with generalized Hubbard on-site interactions. Within a one-loop treatment, we find that an overdamped collective mode develops at low frequency in channels associated with quasi-1D $d_{xz}$ and $d_{yz}$ bands. When the critical point for the $C_4$ symmetry broken phase (structural phase transition) is approached, the overdamped collective modes soften, and acquire increased spectral weight, resulting in non-Fermi liquid behavior at the Fermi surface characterized by the frequency dependence of the imaginary part of electron self energy of the form $\omega^\lambda$, $0<\lambda<1$. We argue that this non-Fermi liquid behavior is responsible for the recently observed zero-bias enhancement in the tunneling signal in quantum point contact spectroscopy. A key experimental test of this proposal is the absence of the non-Fermi liquid behaviour in the hole-doped materials. Our result suggests that quantum criticality plays an important role in understanding the normal state properties of iron-pnictide superconductors.