A new heavy fermion superconductor: the filled skutterudite compound PrOs$_4$Sb$_{12}$

TL;DR

This paper reports the discovery of superconductivity in the filled skutterudite PrOs4Sb12, a heavy fermion compound with unconventional two-phase superconductivity possibly near a quantum critical point.

Contribution

It provides detailed experimental characterization and a proposed energy level scheme for PrOs4Sb12, revealing its unconventional superconducting and quadrupolar properties.

Findings

Superconductivity below 1.85 K with heavy fermion behavior

Unconventional superconductivity with two distinct phases

Presence of quadrupolar order and proximity to a quantum critical point

Abstract

The filled skutterudite compound \PrOsSb{} exhibits superconductivity below a critical temperature $T_\mathrm{c} = 1.85$ K that develops out of a nonmagnetic heavy Fermi liquid with an effective mass $m^{*} \approx 50 m_\mathrm{e}$, where $m_\mathrm{e}$ is the free electron mass. Analysis of magnetic susceptibility, specific heat, electrical resistivity and inelastic neutron scattering measurements within the context of a cubic crystalline electric field yields a Pr$^{3+}$ energy level scheme that consists of a $\Gamma_{3}$ nonmagnetic doublet ground state that carries an electric quadrupole moment, a low lying $\Gamma_{5}$ triplet excited state at $\sim 10$ K, and $\Gamma_{4}$ triplet and $\Gamma_{1}$ singlet excited states at much higher temperatures. The superconducting state appears to be unconventional and to consist of two distinct superconducting phases. An ordered phase of magnetic or quadrupolar origin occurs at high fields and low temperatures, suggesting that the superconductivity may occur in the vicinity of a magnetic or electric quadrupolar quantum critical point.