title: Heavy-fermion superconductivity in the quadrupole ordered state of PrV2Al20.
abstract: PrV2Al20 is a rare example of a heavy-fermion system based on strong hybridization between conduction electrons and nonmagnetic quadrupolar moments of the cubic Γ3 ground doublet. Here, we report that a high-quality single crystal of PrV2Al20 exhibits superconductivity at Tc=50  mK in the antiferroquadrupole-ordered state under ambient pressure. The heavy-fermion character of the superconductivity is evident from the specific heat jump of ΔC/T∼0.3  J/mol K(2) and the effective mass m*/m0∼140 estimated from the temperature dependence of the upper critical field. Furthermore, the high-quality single crystals exhibit double transitions at TQ=0.75  K and T*=0.65  K associated with quadrupole and octupole degrees of freedom of the Γ3 doublet. In the ordered state, the specific heat C/T shows a T(3) dependence, indicating the gapless mode associated with the quadrupole order, the octupole order, or both. The strong sensitivity to impurity of the superconductivity suggests unconventional character due to significant quadrupolar fluctuations.
authors.affiliation: Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Tsujimoto
authors.affiliation: Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Matsumoto
authors.affiliation: Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Tomita
authors.affiliation: Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Akito
authors.initials: A
authors.lastname: Sakai
authors.affiliation: Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan and PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Nakatsuji