Antiferroquadrupolar Ordering in a Pr-Based SuperconductorPrIr2Zn20

Abstract

An antiferroquadrupolar ordering at $T_{\mathrm{Q}}=0.11\mathrm{K}$ has been found in a Pr-based superconductor ${\mathrm{PrIr}}_2{\mathrm{Zn}}_{20}$. The measurements of specific heat and magnetization revealed the non-Kramers ${\Gamma }_3$ doublet ground state with the quadrupolar degrees of freedom. The specific heat exhibits a sharp peak at $T_{\mathrm{Q}}=0.11\mathrm{K}$. The increment of $T_{\mathrm{Q}}$ in magnetic fields and the anisotropic $B-T$ phase diagram are consistent with the antiferroquadrupolar ordered state below $T_{\mathrm{Q}}$. The entropy release at $T_{\mathrm{Q}}$ is only 20% of $R\ln 2$, suggesting that the quadrupolar fluctuations play a role in the formation of the superconducting pairs below $T_{\mathrm{c}}=0.05\mathrm{K}$.