Specific heat and resistivity near the charge-density-wave phase transitions in 2H-TaSe2 and 2H-TaS2

Detailed measurements of the specific heat and resistivity have been made on samples of 2H-TaSe2 and 2H-TaS2 near their charge-density-wave phase transitions. Because the crystal quality of 2H-TaSe2 is much better than that of 2H-TaS2, we emphasize the results on 2H-TaSe2 and make quantitative comparison with the theory of charge-density waves in this material. In 2H-TaSe2 the normal to incommensurate phase transition was found to be second order; the incommensurate to commensurate transition was first order. Specific-heat measurements on this material indicate that the zero-temperature coherence length is relatively short; πξ014 . The resistivity of 2H-TaSe2 immediately above the normal to incommensurate phase transition is dominated by resistive scattering from the periodic structural deformations accompanying the charge-density waves. The specific-heat and resistivity measurements both indicate that the normal to incommensurate phase transition in 2H-TaSe2 can be analyzed within a nearly-mean-field model. © 1977 The American Physical Society.