Strange-metal behavior in ${\mathrm{PrAu}}_2{\mathrm{In}}_4$ with a pseudodoublet ground state

Single crystals of the quasi-one-dimensional ${\mathrm{PrAu}}_2{\mathrm{In}}_4$ have been successfully grown and studied down to very low temperatures. Consistent with the singlet spin-orbit ground state of ${\mathrm{Pr}}^{3+}$, no magnetic ordering is observed in this compound. Nevertheless, ${\mathrm{PrAu}}_2{\mathrm{In}}_4$ reveals a strong magnetic instability arising from the nearly degenerate ground and low-lying singlets that are spaced by only 9 K (termed the pseudodoublet), laying a ground for the competition among crystal field energy, magnetic exchange interaction, and Kondo physics. Moderate Kondo effect comparable to the pseudodoublet spacing is evidenced by a comparative investigation of specific heat and thermopower between ${\mathrm{PrAu}}_2{\mathrm{In}}_4$ and ${\mathrm{LaAu}}_2{\mathrm{In}}_4$. Notably, at $T>2K$, ${\mathrm{PrAu}}_2{\mathrm{In}}_4$ can be smoothly tuned by field to a strange-metal state near 1 T that is reminiscent of quantum critical fluctuations. At the lowest temperatures of $T<1K$, however, such quantum fluctuations are quenched and the compound behaves consistently as a Fermi liquid. The strange-metal behavior visible solely at elevated temperatures is considered generic to Kondo lattices with pseudodoublet ground state of non-Kramers ions, characterized by closely spaced singlets.