The low-temperature ${\mathrm{T}}^2$ rise and the subsequent plateau of the thermal conductivity of glasses allow one to determine two parameters of the phenomenological soft-potential model. The first of these is a weighted average C-bar of the dimensionless parameter combinations ${\mathrm{C}}_{\mathrm{l}}$ and ${\mathrm{C}}_{\mathrm{t}}$ which the soft-potential model shares with the tunneling model. The second is the crossover energy W between tunneling states and vibrations. Values of W and C-bar obtained from the thermal conductivity of ten different glasses agree within experimental error with those obtained from specific-heat and acoustic-absorption data.

• Received 24 May 1996

DOI:https://doi.org/10.1103/PhysRevB.55.5749