Multiband thermal transport in the iron-based superconductor Ba1 xKxFe2As2

TL;DR

This study investigates thermal and electrical transport in Ba1-xKxFe2As2 superconductors, revealing how doping affects electronic structure, charge carriers, and superconducting gap characteristics through detailed measurements.

Contribution

It provides new insights into how potassium doping influences the electronic pockets and superconducting gap structure in Ba1-xKxFe2As2, expanding understanding of multiband thermal transport.

Findings

Electron pocket contracts with K doping but remains significant at high doping levels.

Enhanced Hall-Lorenz number due to small electron pockets in K-doped samples.

Maximum in thermal conductivity appears below Tc in certain doping levels.

Abstract

We present results of precise measurements of the thermal and electrical transport in the optimally- and over-doped Ba1-xKxFe2As2 single crystals (x = 0.35, 0.55, 0.88) and compare them to the previously reported data on Ba(Fe1-yCoy)2As2. A contraction of the electron pocket is observed upon substitution potassium for barium, but even at the extreme doping (x = 0.88) there is still a noticeable contribution from negative charge carriers to the electronic transport. The size of the electron pocket in all K-doped samples is small enough to cause a significant enhancement of the respective Hall-Lorenz number. Another observed characteristic is the emergence of a maximum in the transverse thermal conductivity below the superconducting critical temperature of the optimally- (x = 0.35) and slightly over-doped (x = 0.55) samples. The evolution of this anomaly from the optimally electron-doped Ba(Fe0.94Co0.06)2As2 to hole-overdoped Ba0.45K0.55Fe2As2 suggests formation of a uniform superconducting gap on the electron pocket in the former and regions of a depressed gap on the hole-pocket in the latter.