TMTSF specific heat

The observation of a Meissner flux expulsion [78] and of specific heat anomaly [79] supports the picture of bulk superconductivity (Fig. 21). On a C/T versus T2 plot, the specific heat of (TMTSF)2C104 displays a very large anomaly at 1.2 K and follows the law... 

Figure 21 Superconductivity in (TMTSF)2C104 by transport [10], magnetic [78], and specific heat data [79].

The question whether or not the superconducting state in the Bechgaard salts is of the ordinary BCS type is still under considerable debate. A large variety of different experimental techniques have been employed to elucidate this question. One example was the measurement of the specific heat, C. The result for (TMTSF)2C104 is shown in Fig. 2.11 [113]. At Tc 1.22K a clear... 

On the other hand, the electronic specific heat reveals an important field dependence [62] (Fig. 10). The linear specific heat eoefficient 7 increases from 10 mJ mol K at low field (although larger than the critical field = 1 kOe along c ), and passes through a maximum of 25 mJ mol K at H = 20 kOe for r == 1 K. The locus of the points corresponding to the maximum of 7 in the H -T plane is located in the paramagnetic domain of (TMTSF)2C104, i.e. not to... 

Figure 9 Specific heat as a function of temperature in (TMTSF)2C104 near the superconducting transition, after [61].

Figure 10 Magnetic field dependence of the Sommerfeld constant of specific heat in (TMTSF)2C104 at low temperature, after [62].

Figures 3 and 4 illustrate for the (TMTSF)2C104 compound, the two main effects of the cooling rate. The first effect concerns the shift of the threshold field, as displayed on Fig. 3 the threshold fields corresponding to quenched and relaxed states are represented by solid and dashed arrows, respectively. This shift is responsible for the discrepancy we observed between the threshold fields, as determined by specific heat or by magnetocaloric effect measurements 31,32 fact. Figure 3 leads to a first conclusion in order to construct a coherent phase diagram, all the experiments are to be performed for the same cooling rate, at...

The specific heat measurements (Table 10.2) indicate AC/yT). is 1.50 0.15 or >2 (-2.8) for the Cu(NCS)2 salt and 2 0.5 for the Cu[N(CN)2]Br salt. These values are close to or a little higher than the BCS value. The values (215 10 K, 210 15 K) are similar to those for (TMTSF)2C104. The superconducting gaps of the CufNCSlj and Cu[N(CN)2]Br were examined by a tuimeling spectroscopic method, magnetic field penetration depth measurements by AC susceptibility, pSR, microwave in5)ed-ance, etc. The results, however, are inconsistent and controvCTsial (some claim an anisotropic gap or zero gap non-BCS type, another claims normal BCS type). 

---