Pressure-induced super heavy fermion state and antiferromagnetism in YbIr₂Zn₂₀

We studied an effect of pressure on the electronic state of YbIr ₂Zn₂₀under magnetic fields. The heavy fermion state at ambient pressure is found to be changed into an antiferromagnetic state at pressures larger than a critical pressure P_c≃ 5.2 GPa, where the electronic state indicates a superheavy fermion state with an order of the electronic specific specific heat coefficient γ = 20 J/(K ²·mol). The temperature dependence of the electrical resistivity shows a characteristic two-peak structure above 5.0 GPa, implying the combined phenomena between the Kondo effect and the crystalline electric field effect. At 7.6 GPa, the magnetoresistance shows a broad maximum at a critical field H_c, corresponding to a pressure-induced antiferromagnetic phase with the Néel temperature T_N = 1.4 K. TN increases with further increasing pressure.