A theory of new type of heavy-electron superconductivity in PrOs_4Sb_12: quadrupolar-fluctuation mediated odd-parity pairings

TL;DR

This paper proposes a theoretical framework explaining the unconventional heavy-electron superconductivity in PrOs_4Sb_12, emphasizing quadrupolar fluctuations and odd-parity pairing, aligning with recent experimental observations.

Contribution

It introduces a unified theory incorporating crystal electric field effects, Fermi surface shape, and quasiparticle structure to explain the superconducting state of PrOs_4Sb_12.

Findings

Chiral p-wave states are favored under magnetic fields due to orbital Zeeman effect.

p_x+ip_y states are stabilized by magnetic field, while p_x states are stabilized without it.

Double superconducting transition can occur due to spin-orbit coupling in triplet pairs.

Abstract

It is shown that unconventional nature of superconducting state of PrOs_4Sb_12, a Pr-based heavy electron compound with the filled-Skutterudite structure, can be explained in a unified way by taking into account the structure of the crystalline-electric-field (CEF) level, the shape of the Fermi surface determined by the band structure calculation, and a picture of the quasiparticles in f$^{2}$-configuration with magnetically singlet CEF ground state. Possible types of pairing are narrowed down by consulting recent experimental results. In particular, the chiral "p"-wave states such as p_x+ip_y is favoured under the magnetic field due to the orbital Zeeman effect, while the "p"-wave states with two-fold symmetery such as p_x can be stabilized by a feedback effect without the magnetic field. It is also discussed that the double superconducting transition without the magnetic field is possible due to the spin-orbit coupling of the "triplet" Cooper pairs in the chiral state.