Strange-metal behavior in PrAu2In4 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 $T>2\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, ${\mathrm{PrAu}}_{2}{\mathrm{In}}_{4}$ 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 $T<1\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, 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.