We report on measurements of the thermal conductivity ${\mathrm{\kappa }}_{\mathrm{T}}$ close to the Peierls transition temperature ${\mathrm{T}}_{\mathrm{P}}$ in ${\mathrm{K}}_{0.3}$${\mathrm{MoO}}_3$ and (${\mathrm{TaSe}}_4$${)}_2$I. In both cases there is an enhancement of ${\mathrm{\kappa }}_{\mathrm{T}}$ that peaks at the transition. Simultaneous measurements of the specific heat suggest that the anomalous behavior is a result of mode occupation rather than changes in electron- or phonon-scattering processes.

• Received 30 January 1989

DOI:https://doi.org/10.1103/PhysRevLett.63.895