Linkage between scattering rates and superconductivity in doped ferropnictides

TL;DR

This study reveals a linear energy-dependent scattering rate in doped ferropnictides that peaks near optimal doping and correlates with superconductivity, supporting a spin fluctuation pairing mechanism.

Contribution

It provides the first detailed ARPES analysis linking scattering rates and superconductivity in doped ferropnictides, highlighting the role of incoherent charge carriers.

Findings

Scattering rate is linear in energy and independent of doping.

Maximum scattering rate slope occurs near optimal doping.

Scattering rate exceeds the Planckian limit in optimally doped samples.

Abstract

We report an angle-resolved photoemission study of a series of hole and electron doped iron-based superconductors, their parent compound BaFe2As2, and their cousins BaCr2As2 and BaCo2As2. We focus on the energy (E) dependent scattering rate Gamma(E) as a function of the 3d count and on the renormalization function Z(E) of the inner hole pocket, which is the hot spot in these compounds. We obtain a non-Fermi-liquid-like linear in energy scattering rate Gamma(E>> kBT), independent of the dopant concentration. The main result is that the slope beta=Gamma(E >> kBT)/E, reaches its maxima near optimal doping and scales with the superconducting transition temperature. This supports the spin fluctuation model for superconductivity for these materials. In the optimally hole-doped compound, the slope of the scattering rate of the inner hole pocket is about three times bigger than the Planckian limit Gamma(E)/E~1. This result together with the energy dependence of the renormalization function Z(E) signals very incoherent charge carriers in the normal state which transform at low temperatures to a coherent unconventional superconducting state.