Thermal properties of layered transition-metal dichalcogenides at charge-density-wave transitions

The heat capacity and resistivity at the charge-density-wave (CDW) transitions of several layered transition-metal dichalcogenides are presented. The magnitude of the thermal and resistive anomalies in the 2H polytypes indicates only a small fraction of the Fermi surface is involved in the CDW distortion. The transition from the normal to the incommensurate CDW state at T0 is second order, while the transition to the commensurate CDW state at Td is first order. However, the heat capacity anomaly at T0, especially in 2H-TaSe2, does not show the simple BCS-like jump expected from Landau models, rather a peak in the heat capacity occurs at T0. © 1977 The American Physical Society.