Unusual Increase of Electron Thermal Conductivity Caused by a Pseudogap at the Fermi Level

摘要

At high temperatures above 200 K, a significant increase in thermal conductivity, κ(T), was observed for the Al-based complex structure alloys, Al_82.6−x Re_17.4Si _x and Al_82.6−x Mn_17.4Si _x (7 ≤ x ≤ 11), in which 138 atoms exist in a large cubic unit cell with a lattice constant of a ≈ 1.2 nm. By analyzing the measured κ(T) in terms of the electronic density of states determined both by the low-temperature specific heat measurement and a band calculation, we found that the increase in κ(T) at high temperatures is most pronounced when the Fermi level (Ɛ _F) is located at the local minimum of the electronic density of states (pseudogap). The behavior of κ(T) at high temperature is almost quantitatively accounted for using the linear response theory with the theoretically calculated electronic density of states. These facts unambiguously indicate that the large increase in κ(T) is not brought about by the lattice but by the electrons in the pseudogap persisting at Ɛ _F.