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

摘要

In hole-doped high-Tc superconductors, thermal conductivity increasesdrastically just below Tc, which has been considered as a hallmark of a nodalgap. In contrast, such a coherence peak in thermal conductivity is not visiblein 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 inthe Hubbard model using the fluctuation-exchange (FLEX) approximation, whichpredicts that the nodal d-wave state is realized in both hole-doped andelectron-doped compounds. The contrasting behavior of thermal conductivity inboth compounds originates from the differences in the hot/cold spot structure.In general, a prominent coherence peak in thermal conductivity appears inline-node superconductors only when the cold spot exists on the nodal line.