Unscreening Effect on Fe-Pnictide Superconductor

TL;DR

This paper investigates how unscreening of Coulomb interactions enhances superconductivity in Fe-pnictides, explaining the inverse relationship between T_c and density of states through a microscopic mechanism.

Contribution

It introduces a microscopic model incorporating unscreening effects, revealing their role in increasing T_c despite decreasing density of states in Fe-pnictide superconductors.

Findings

Superconducting T_c increases with electron doping due to unscreening.

Spin-density wave T_s decreases rapidly with doping.

Provides a microscopic explanation for the T_c and density of states relationship.

Abstract

We study a microscopic mechanism of Fe-pnictide superconductor, considering the screening effects of Coulomb interaction in addition to the conventional spin-fluctuation mechanism. It is shown that, by electron doping, the transition temperature of superconductivity increases due to the "unscreening" effect even though the density of states decrease, while that of spin-density wave rapidly decreases due to breaking of nesting conditions. Our results give a clear interpretation to the mystery of interrelation between T_c and the density of states observed in the Fe-pnictide superconductors.