The mechanism of hole carrier generation and the nature of pseudogap- and 60K-phases in YBCO

TL;DR

This paper presents a model explaining hole carrier generation and the pseudogap phase in YBCO, showing quantitative agreement with experimental data and suggesting the pseudogap's superconducting nature arising from fluctuations in small clusters.

Contribution

The paper introduces a model based on NUC formation on Cu pairs that explains hole doping, pseudogap, and 60K phases in YBCO, aligning well with experimental observations.

Findings

Calculated hole concentration matches experimental data.

Pseudogap has a superconducting nature arising from cluster fluctuations.

Temperature dependences of pseudogap and transition temperatures agree with experiments.

Abstract

In the framework of the model assuming the formation of NUC on the pairs of Cu ions in CuO$_{2}$ plane the mechanism of hole carrier generation is considered and the interpretation of pseudogap and 60 K-phases in $YBa_{2}Cu_{3}O_{6+\delta}$. is offered. The calculated dependences of hole concentration in $YBa_{2}Cu_{3}O_{6+\delta}$ on doping $\delta$ and temperature are found to be in a perfect quantitative agreement with experimental data. As follows from the model the pseudogap has superconducting nature and arises at temperature $T^{*}>T_{c\infty}>T_{c}$ in small clusters uniting a number of NUC's due to large fluctuations of NUC occupation. Here $T_{c\infty}$ and $T_{c}$ are the superconducting transition temperatures of infinite and finite clusters of NUC's, correspondingly. The calculated $T^{*}(\delta)$ and $T_{n}(\delta)$ dependences are in accordance with experiment. The area between $T^{*}(\delta)$ and $T_{n}(\delta)$ corresponds to the area of fluctuations where small clusters fluctuate between superconducting and normal states owing to fluctuations of NUC occupation. The results may serve as important arguments in favor of the proposed model of HTSC.