Evidence for the Quadrupolar Kondo Effect in the Heavy Fermion Superconductor PrV2Al20
The non-Fermi liquid (NFL) phase holds abiding fascination owing to its prime connections with unconventional superconductivity and other intriguing emergent quantum states in itinerant electron systems. Magnetic heavy-fermion metals offer some prototypical examples of the NFL as a result of the competing interplay between the magnetic Kondo effect and the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction among local dipolar moments. Such NFL often appears at the boundary of magnetic instability and is attributed to quantum criticality.
Heavy fermion metals hosting multipolar local moments entail a new route to exotic spin-orbital entangled quantum phases. In the case of quadrupolar systems, the conventional Kondo effect is replaced by a two-channel Kondo mechanism, known as the quadrupolar Kondo effect. Here Kondo entanglement takes place between the quadrupolar moments of f-electrons and the orbital fluctuations of the conduction electrons, while the conduction electron spins offer two separated scattering channels. This effect is considered a key mechanism behind the orbital-driven NFL behavior and quantum critical phenomena. The heavy fermion superconductor PrV2Al20 possesses a nonmagnetic ground-state doublet, featuring both electric quadrupoles and magnetic octupoles. It exhibits novel NFL behavior above the antiferroquadrupolar ordering transition at ambient pressure, with ~ √T dependent resistivity and ~ −√T magnetic susceptibility. The relation of this NFL phase with the quadrupolar Kondo effect is yet to be explored.
We report a comprehensive study of the NFL phenomena in PrV2Al20 single crystals based on magnetoresistance (MR), magnetic susceptibility, and specific heat measurements obtained under a  magnetic field. Upon entering the NFL regime, we observed a universal scaling behavior expected for the quadrupolar Kondo lattice, which reveals the vital role of the quadrupolar Kondo effect in shaping the NFL phase of PrV2Al20. Deviations from this scaling relation occur below about 8 K, accompanied by a negative MR and a power-law divergent specific heat. Such behavior signifies the emergence of an anomalous low-temperature state, which is likely driven by heavy-fermion coherence in the quadrupolar Kondo lattice or critical quantum fluctuations of multipolar moments.
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