A Universal Intrinsic Scale of Hole Concentration for High-Tc Cuprates

TL;DR

This study introduces a universal scale based on thermoelectric power to accurately measure hole concentration in high-Tc cuprates, revealing consistent pseudogap behaviors and clarifying the relationship between doping, pseudogaps, and superconductivity.

Contribution

The paper proposes a universal intrinsic scale for hole concentration using thermoelectric power, unifying measurements across different cuprates and clarifying pseudogap phenomena.

Findings

Thermoelectric power at room temperature correlates with hole concentration across cuprates.

Universal phase diagram for pseudogap temperatures as a function of hole concentration.

Pseudogaps are intrinsic to doped holes, but Tc depends on inter-layer coupling.

Abstract

We have measured thermoelectric power (TEP) as a function of hole concentration per CuO2 layer, Ppl, in Y1-xCaxBa2Cu3O6 (Ppl = x/2) with no oxygen in the Cu-O chain layer. The room-temperature TEP as a function of Ppl, S290(Ppl), of Y1-xCaxBa2Cu3O6 behaves identically to that of La2-zSrzCuO4 (Ppl = z). We argue that S290(Ppl) represents a measure of the intrinsic equilibrium electronic states of doped holes and, therefore, can be used as a common scale for the carrier concentrations of layered cuprates. We shows that the Ppl determined by this new universal scale is consistent with both hole concentration microscopically determined by NQR and the hole concentration macroscopically determined by the Cu valency. We find two characteristic scaling temperatures, TS* and TS2*, in the TEP vs. temperature curves that change systematically with doping. Based on the universal scale, we uncover a universal phase diagram in which almost all the experimentally determined pseudogap temperatures as a function of Ppl fall on two common curves; upper pseudogap temperature defined by the TS* versus Ppl curve and lower pseudogap temperature defined by the TS2* versus Ppl curve. We find that while pseudogaps are intrinsic properties of doped holes of a single CuO2 layer for all high-Tc cuprates, Tc depends on the number of layers, therefore the inter-layer coupling, in each individual system.