•K. Grube¹, S. Drobnik², C. Pfleiderer², A. Faisst², R. Vollmer², H. v. Löhneysen^1,2, E.D. Bauer³ und M.B. Maple^3
3Department of Physics and Institute of Pure and Applied Physical Sciences, University of California San Diego, La Jolla, California 92093-0319
¹Forschungszentrum Karlsruhe, Institut für Festkörperphysik, D-76021 Karlsuhe
²Physikalisches Institut, Universität Karlsruhe, D-76128 Karlsuhe

PrOs₄Sb₁₂ is the first Pr based heavy-fermion superconductor. Detailed measurements of the low temperature specific heat [1] have helped identify the superconductivity in PrOs₄Sb₁₂ as a strong contender for quadrupolar pairing, i.e., superconductivity that is neither electron-phonon nor magnetically mediated. Here we focus on a related issue, the formation of an ordered phase at low temperatures and high magnetic fields, that appears to be connected with the Zeeman splitting of the crystal electric field ground state. We have revisited this high field phase in a detailed study of the specific heat up to 14 T at temperatures down to 0.4 K. The possible nature of the high-field phase is discussed in the context of the crystal field ground state and the evidence for several superconducting phases.

[1] R. Vollmer et al., Phys. Rev. Lett. 90 (2003) 057001.