Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTi$_2$Al$_{20}$

TL;DR

This paper reports the discovery of type-II superconductivity at 200 mK in the quadrupolar Kondo lattice compound PrTi$_2$Al$_{20}$, highlighting the interplay between quadrupolar ordering and superconductivity in a strongly hybridized electron system.

Contribution

It demonstrates superconductivity emerging within the ferroquadrupolar state of PrTi$_2$Al$_{20}$, a novel finding linking quadrupolar order and superconductivity in a Kondo lattice.

Findings

Superconductivity at $T_c = 200$ mK observed in PrTi$_2$Al$_{20}$.

Superconductivity occurs in the nonmagnetic ferroquadrupolar state.

Effective mass of quasiparticles is approximately 16 times the free electron mass.

Abstract

The cubic compound PrTi$_2$Al$_{20}$ is a quadrupolar Kondo lattice system that exhibits quadrupolar ordering due to the non-Kramers $\Gamma_3$ ground doublet and has strong hybridization between $4f$ and conduction electrons. Our study using high-purity single crystal reveals that PrTi$_2$Al$_{20}$ exhibits type-II superconductivity at $T_{\rm c} = 200$ mK in the nonmagnetic ferroquadrupolar state. The superconducting critical temperature and field phase diagram suggests moderately enhanced effective mass of $m^*/m_0 \sim 16$.