Thermoelectric response of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$: evidence for strong correlation and low carrier density

TL;DR

This study investigates the thermoelectric properties of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$, revealing it as a low-density, strongly correlated superconductor with significant superconducting fluctuations and a low Fermi temperature.

Contribution

The paper provides the first detailed thermoelectric measurements of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ up to high magnetic fields, identifying its low carrier density and strong electronic correlations.

Findings

Large Seebeck coefficient indicating low Fermi temperature

Identification of strong electronic correlations in the material

Presence of significant superconducting fluctuations

Abstract

We present a study of the Seebeck and Nernst coefficients of Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ extended up to 28 T. The large magnitude of the Seebeck coefficient in the optimally doped sample tracks a remarkably low normalized Fermi temperature, which, like other correlated superconductors, is only one order of magnitude larger than T$_c$. We combine our data with other experimentally measured coefficients of the system to extract a set of self-consistent parameters, which identify Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ as a low-density correlated superconductor barely in the clean limit. The system is subject to strong superconducting fluctuations with a sizeable vortex Nernst signal in a wide temperature window.