Thermoelectric power and Hall coefficient measurements on Ba(Fe(1-x)TMx)2As2 (TM = Co and Cu)

TL;DR

This study measures thermoelectric power and Hall coefficient in Ba(Fe1-xTMx)2As2 with TM = Co and Cu, revealing electronic structure changes related to superconductivity and magnetic transitions.

Contribution

It provides new insights into how electron doping affects Fermi surface modifications and the emergence of superconductivity in iron-based compounds.

Findings

Significant changes in TEP and Hall coefficient at critical doping levels.

Similar electronic modifications occur in Cu-doped samples without superconductivity.

Suppression of magnetic/structural transitions alone is not sufficient for superconductivity.

Abstract

Temperature dependent thermoelectric power (TEP) data on Ba(Fe1-xTMx)2As2 (TM = Co and Cu), complemented by the Hall coefficient data on the samples from the same batches, have been measured. For Co-doping we clearly see a change in the temperature dependent TEP and Hall coefficient data when the sample is doped to sufficient $e$ (the number of extra electrons associated with the TM doping) so as to stabilize low temperature superconductivity. Remarkably, a similar change is found in the Cu-doped samples at comparable e-value, even though these compounds do not superconduct. These changes possibly point to a significant modification of the Fermi surface / band structure of Ba(Fe1-xTM_x)2As2 at small electron doping, that in the case of Co-doping is just before, and probably allows for, the onset of superconductivity. These data further suggest that suppression of the structural / magnetic phase transition and the establishment of a proper e-value are each necessary but, individually, not sufficient conditions for superconductivity.