Specific heat and ac susceptibility studies of the superconducting phase diagram ofPrOs4Sb12

Abstract

We report on ac-susceptibility and heat-capacity measurements of the superconductor PrOs 4 Sb 12 in magnetic fields. The resulting phase diagram reveals two distinguishable superconducting phases with transitions at the upper critical field B c2 and a slightly lower field B c2 * . Between B c2 * and 0.7ϫ B c2 * the ac-susceptibility data shows a region with enhanced pinning properties characterized by an extended peak effect. The heat-capacity data reveal an extremely strongly coupled superconductivity with a considerable contribution of heavy quasiparticles. This unusual strong-coupling behavior originates in a sharp increase of the superfluid density at T c . The decrease of the discontinuity of the specific heat at T c and the corresponding pronounced increase of the Ginzburg-Landau-Maki parameter 2 indicate that the superconductivity is most probably not Pauli limited in a large temperature range.

Double superconducting transition in the filled skutteruditePrOs4Sb12and sample characterizations

“…These result confirm that the Pr atom is in a strongly disordered position as reported in 8,30 . Moreover, they seem to indicate the possibility of a nearly but not completely filled Pr site in the filled skutterudite structure for PrOs 4 Sb 12 .…”

“…Ever since, a plethora of publications have dealt with its observation and with possible theories. This double transition has since been observed by specific heat measurements by many groups (from Japan 4 , USA 3,5 , Germany 2,7,8,9 , France 10 ) and by thermal expansion 11 with samples from different origins and even in La doped or Ru substituted samples 5,12 . So whatever the origin, the double transition is a robust property of this compound and we will see that it appears in good samples.…”

Superconducting phases off-electron compounds

“…Although the low temperature specific heat is dominated by a Schottky anomaly around 2 K, it is possible to infer a strongly enhanced linear term in the normal state specific heat C/T ≈ 0.2 to 0.75 J/mol K 2 (for a comprehensive discussion of the analysis of C(T ) see (Grube et al, 2006) and references therein). A related large anomaly is observed in the specific heat at the superconducting transition, ∆C/T s ≈ 0.5 J/mol K 2 , which, depending on the strength of the coupling, also points to a large value of γ. Finally,H c2 ∼ 2.2 T is close to the orbital limit H orb c2 = 2.4 T, inferred from the experimentally observed variation dH c2 /dT ≈ −1.9 T/K near T s .…”

Limits on superconductivity-related magnetization inSr2RuO4andPrOs4Hicks1, Kirtley2, Lippman3 et al. 2010Phys. Rev. B18672052View full textAdd to dashboardCite

“…5,6 Measurements of specific heat show an unusual double superconducting transition, with T c1 Ϸ 1.86 K and T c2 Ϸ 1.70 K. [7][8][9] The coherence length of PrOs 4 Sb 12 is = 12 nm, while muon spin rotation ͑SR͒ measurements yield ͑0͒Ϸ350 nm. 10,11 Sr 2 RuO 4 and PrOs 4 Sb 12 both have unusual superconducting states.…”