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on different sheets of the Fermi surface, or from an in- trinsically anisotropic gap(s). 

We turn now to the information contained in the mag- netic field dependence of γ . The inset to Fig. 1 shows the suppression of the superconducting anomaly in mag- netic fields from 1 to 13T in 1T increments. Because the phonon specific heat is independent of magnetic field, the change in electronic specific heat with field is obtained by subtracting the zero field data from the data measured in a field (see Fig. 4(a)). 

Integrating over temperature gives the change in elec- 

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tronic entropy with field (see Fig. 4(b)). 

The change in free energy is obtained by integrating the entropy over temperature (see Fig. 4(c)). 

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Δ F ( H, 0) is determined from the condition that the su- perconducting contribution to Δ F ( H, T ) tends to zero for T ≫ T$_{c}$ . At each temperature, the field dependence of the free energy is fitted to a theoretical expression de- rived from the model of Hao and Clem[18] for an s -wave superconductor. 

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The coefficients a and β are weakly field dependent and are given by a ∼ 0 . 77 and β ∼ 1 . 44 in the range 0 . 02 < H/H$_{c}$$_{2}$ < 0 . 3. A fit to the free energy at 2.5K is shown in the inset to Fig. 4(c). 

The penetration depth, λ , and the upper critical field, H$_{c}$$_{2}$, are determined directly from the fit parameters a$_{1}$ and a$_{2}$ . Then using the following Ginsburg-Landau rela- tions we extract the: critical field H 2 c = ( φ$_{0}$/ 4 πλ $^{2}$) H$_{c}$$_{2}$ , 

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