ac-Calorimetry of (TMTSF)2PF6

We have searched for dynamic thermal effects in (TMTSF)2PF6 by measuring its specific heat with ac calorimetry. Near its spin-density-wave transition (Tc=12 K), the magnitude of the specific heat is the same as that measured in quasi-static measurements, indicating that there are no kinetic contributions to the specific heat at these temperatures. The anomaly at Tc is consistent with the Ehrenfest relation estimate for a continuous phase transition. No anomalies are observed in a pellet of (TMTSF)2PF6 mixed with KBr at Tc or the expected “spin-density-wave glass” transition (Tg∼3.5 K), suggesting that residual disorder in the pellet freezes in a glassy state at Tc.