Specific heat of Nb3Sn:: The case for a second energy gap -: art. no. 184526

We present specific-heat data for Nb3Sn, a well-known technically applied superconductor with a critical temperature T(c)congruent to18 K, in the temperature range from 1.2 to 200 K in zero magnetic field, and from 1.5 to 22 K in fields Hless than or equal to16 T. The particularly dense and homogeneous polycrystalline sample used for this study is characterized in detail. We determine the bulk upper critical field H-c2(T) from specific-heat data, and the Sommerfeld constant gamma from the entropy S(T). We investigate in detail a low-temperature anomaly already noticed in previous investigations in zero field, and find that this feature can be quantitatively ascribed to the presence of a second superconducting gap 2Delta(S)(0)congruent to0.8k(B)T(c), in addition to the main one 2Delta(L)(0)congruent to4.9k(B)T(c). The signature of this minor gap, which affects 7.5% of the electronic density-of-states, vanishes in high fields.