Charge carriers of different origin in cuprates as revealed by experiment

TL;DR

This study investigates the origin and behavior of charge carriers in cuprates, revealing that their number exceeds doping levels at high doping and varies with temperature, affecting the phase diagram.

Contribution

It provides experimental evidence that charge carriers in cuprates originate from multiple sources and are influenced by temperature and doping, challenging simpler models.

Findings

Carrier number exceeds doping level at high doping

Activation energy relates to Fermi surface features

Crossover temperature aligns with carrier activation

Abstract

The Hall coefficient data for cuprates show that number of carriers exceeds external doping $x$ at higher $x$ and varies with temperature. Hence, spins on the Cu-sites are not conserved. Activation energy for thermally excited carriers equals the energy between the Fermi surface "arc" and the band bottom near the van Hove singularities. Crossover from marginal Fermi liquid- to pseudogap- regime happens at temperatures at which number of activated carriers gets comparable with the number of externally doped holes. Implications for the $(T,x)$-phase diagram of cuprates are discussed.