Thermopower across the pseudogap critical point of La(1.6-x)Nd(0.4)Sr(x)CuO(4): Evidence for a quantum critical point in a hole-doped high-Tc superconductor

TL;DR

This study investigates thermopower behavior near the pseudogap critical point in a high-Tc superconductor, revealing signatures of a quantum critical point and potential order reconstruction affecting electronic properties.

Contribution

It provides evidence for a quantum critical point at the pseudogap critical doping in La(1.6-x)Nd(0.4)Sr(x)CuO(4), linking thermopower behavior to Fermi surface reconstruction.

Findings

S/T varies as ln(1/T) above p*

Large increase in S/T below T* below p*

Linear resistivity above p* and upturn below T*

Abstract

The thermopower S of the high-Tc superconductor La(1.6-x)Nd(0.4)Sr(x)CuO(4) was measured as a function of temperature T near its pseudogap critical point, the critical hole doping p* where the pseudogap temperature T* goes to zero. Just above p*, S/T varies as ln(1/T) over a decade of temperature. Below p*, S/T undergoes a large increase below T*. As with the temperature dependence of the resistivity, which is linear just above p* and undergoes a large upturn below T*, these are typical signatures of a quantum phase transition. This suggests that p* is a quantum critical point below which some order sets in, causing a reconstruction of the Fermi surface, whose fluctuations are presumably responsible for the linear-T resistivity and logarithmic thermopower. We discuss the possibility that this order is the "stripe" order known to exist in this material.