Importance of Fermi surface topology for high temperature superconductivity in electron-doped iron arsenic superconductors

TL;DR

This study shows that changes in Fermi surface topology, especially the presence of central hole pockets, are crucial for high-temperature superconductivity in electron-doped iron arsenic superconductors, with Lifshitz transitions correlating with Tc suppression.

Contribution

It provides experimental evidence linking Fermi surface topology changes to the suppression of superconductivity in overdoped Ba(Fe1-xCox)2As2, highlighting the importance of Fermiology.

Findings

Lifshitz transitions occur at high doping levels.

Superconductivity vanishes when central hole pockets disappear.

Presence of central hole pockets is necessary for high Tc.

Abstract

We used angle resolved photoemission spectroscopy and thermoelectric power to study the poorly explored, highly overdoped side of the phase diagram of Ba(Fe1-xCox)2As2 high temperature superconductor. Our data demonstrate that several Lifshitz transitions - topological changes of the Fermi surface - occur for large x. Tc starts to decrease with doping when the cylindrical, central hole pocket changes to ellipsoids centering at the Z point, and goes to zero before these ellipsoids disappear around x = 0.2. Changes in thermoelectric power occur at similar x-values. Beyond this doping level the central pocket changes to electron-like and superconductivity does not exist. Our observations reveal the crucial importance of the underlying Fermiology in this class of materials. A necessary condition for superconductivity is the presence of the central hole pockets rather than perfect nesting between central and corner pockets.