Theory of Thermal Conductivity in High-Tc Superconductors below Tc: Comparison between Hole-Doped and Electron-Doped Systems

TL;DR

This paper investigates the differing thermal conductivity behaviors in hole-doped and electron-doped high-Tc superconductors below Tc, attributing differences to hot/cold spot structures and using the Hubbard model with FLEX approximation.

Contribution

It demonstrates that the contrasting thermal conductivity behaviors are due to hot/cold spot structures, providing a theoretical explanation for experimental observations.

Findings

Nodal d-wave state is predicted in both systems.

Coherence peak appears only with cold spots on the nodal line.

Differences in hot/cold spot structures explain thermal conductivity behavior.

Abstract

In hole-doped high-Tc superconductors, thermal conductivity increases drastically just below Tc, which has been considered as a hallmark of a nodal gap. In contrast, such a coherence peak in thermal conductivity is not visible in electron-doped compounds, which may indicate a full-gap state such as a (d+is)-wave state. To settle this problem, we study the thermal conductivity in the Hubbard model using the fluctuation-exchange (FLEX) approximation, which predicts that the nodal d-wave state is realized in both hole-doped and electron-doped compounds. The contrasting behavior of thermal conductivity in both compounds originates from the differences in the hot/cold spot structure. In general, a prominent coherence peak in thermal conductivity appears in line-node superconductors only when the cold spot exists on the nodal line.