Specific heat ofNb3Sn: The case for a second energy gap

Abstract

We present specific-heat data for Nb 3 Sn, a well-known technically applied superconductor with a critical temperature T c Х 18 K, in the temperature range from 1.2 to 200 K in zero magnetic field, and from 1.5 to 22 K in fields H ഛ 16 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 ͑T͒ from specific-heat data, and the Sommerfeld constant ␥ from the entropy S͑T͒. 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 2⌬ S ͑0͒Х0.8k B T c , in addition to the main one 2⌬ L ͑0͒Х4.9k B T c . The signature of this minor gap, which affects 7.5% of the electronic density-of-states, vanishes in high fields.

Towards analysis of the electron density of states of Nb3Sn as a function of strain

“…This has been observed and commented on a number of times in literature [6,12,24]. A likely explanation is that phenomenon is related to compositional inhomogeneity, similar to the effects observed in wires [22], noting that the sample is not perfectly homogeneous but rather a mixture of compositions ranging from Nb 0.…”

Low-temperature specific heat of the superconductor Mo3Sb7

“…We may add that two-band gap feature has been found in some superconductors, except for MgB 2 mentioned above, also in YbNi 2 B 2 C [22] and Nb 3 Sn [23].…”

Thermal fluctuations and vortex melting in theNb3Snsuperconductor from high resolution specific heat measurements

“…We thus normalize the ⌬S value by the coherence length ͑ = 36 Å for Nb 3 Sn͒ which extends in Nb 3 Sn over a few lattice parameters ͑5.293 Å͒. 12 We find 0.3± 0.1 k B / vortex/ , comparable to the value of YBCO and thus a reasonable value for a vortex-melting transition. A four times smaller value is derived from the AC specific-heat data in 6 T indicating an underestimation of the latent heat due to the presence of a temperature hysteresis and thus confirming the first-order nature of the transition.…”