Specific heat of TSeF-TCNQ

We have measured the specific heat of single crystals of TSeF-TCNQ. Anomalies are observed at T_a = 28 K and T_b = 33 K, indicating that there are two phase transitions, presumably reflecting the separate condensation of the charge-density-wave on the TSeF and TCNQ conducting chains. The total increase of the specific heat on cooling through both transitions is larger than the value estimated from mean-field theory, as expected for transitions in a quasi-one dimensional material, but, because of the proximity of the two transitions, it is not possible to unambiguously determine the specific heat baseline and hence the magnitude of the specific heat step. A sharp peak in specific heat is also observed at T_a; if the entropy contained in this peak is to be associated with locking of the charge-density-wave phases on the two conducting chains, its large size implies a surprisingly small phase coherent volume.