Specific heat versus field in the 30 K superconductorBaFe2(As0.7P0.3)

Abstract

Abstract:We report specific heat measurements on the Fe-based superconductor BaFe 2 (As 0.7 P 0.3 ) 2 , a material on which previous penetration depth, NMR, and thermal conductivity measurements have observed a high density of low-energy excitations, which have been interpreted in terms of order parameter nodes. Within the resolution of our measurements, the low temperature limiting C/T is found to be linear in field, i.e. we find no evidence for a Volovik effect associated with nodal quasiparticles in either the clean or dirty limit. We discuss possible reasons for this apparent contradiction.

Superconducting gap evolution in overdopedBaFe2(As1−xPx)2single crystals through nanocal

“…[14] and [15], which report ∼ 5 − 8 meV for the gap on the hole pockets and ∼ 7 − 8 meV on the electron pockets. The values seem in good agreement considering that we are slightly out of optimally doped conditions and that the specific heat signal is more sensitive to the hole pockets (see [40] and references therein). P overdoping has the effect of reducing the main superconducting gap and increasing the weight of the second gap.…”

Effect of annealing on the specific heat of Ba(Fe1−xCox)Gofryk1, Vorontsov2, Vekhter3 et al. 2011Phys. Rev. B

“…This is also true for other Fe-based superconductors (see for instance Ref. [42][43][44]. Clearly there are additional low energy excitations not captured by a single gap and, at least, a two gap scenario is necessary to describe the experimental results in this system 8,10,38,41 .…”

Gap symmetry and structure of Fe-based superconductors

“…Note that the underdoped sample is in the SDW-SC coexistence phase. In the isovalent analog system BaFe 2 (As 1−x P x ) 2 , an early report of linear-H behavior which appeared inconsistent with penetration depth measurements [223] reporting linear T behavior as discussed above [205], as well as evidence for nodes from NMR [149] and thermal conductivity measurements [205], was recently superseded by a measurement reporting a small Volovik term at low fields crossing over to linear behavior at higher fields [224]. This work underlined the importance of determining on which sheets the nodes occur, since sheets with smaller mass and longer relaxation times will dominate transport, while larger mass alone will determine specific heat.…”