Positive Seebeck coefficient in highly doped La$_{2-x}$Sr$_x$CuO$_4$ ($x$=0.33); its origin and implication

TL;DR

This study reveals a positive Seebeck coefficient in heavily overdoped La$_{1.67}$Sr$_{0.33}$CuO$_4$, indicating complex scattering mechanisms and electron-hole asymmetry that influence superconductivity.

Contribution

It demonstrates the origin of positive Seebeck coefficient in overdoped cuprates and links it to scattering time asymmetry affecting superconductivity.

Findings

Positive Seebeck coefficient despite electron-like Fermi surface

Energy-dependent scattering time causes electron-hole asymmetry

Implication for suppression of Cooper pairing along nodal directions

Abstract

We present a study of the thermoelectric (Seebeck and Nernst) response in heavily overdoped, non-superconducting La$_{1.67}$Sr$_{0.33}$CuO$_4$. In spite of the electron-like curvature of the Fermi surface, the Seebeck coefficient is positive at low temperatures. Such a feature, previously observed in copper, silver, gold and lithium, is caused by a non-trivial energy dependence of the scattering time. We argue that this feature implies a strong asymmetry between the lifetime of occupied and unoccupied states along the zone diagonals and such an electron-hole asymmetry impedes formation of Cooper pairs along the nodal direction in the superconducting ground state emerging at lower doping levels.