Quantum critical phenomena in heavy fermion compound YbIr ₂Zn₂₀

We measured the electrical resistivity under pressure and magnetic field for a heavy fermion compound YbIr₂Zn₂₀ with a cubic cage structure. Metamagnetic transition, which is characteristic in the heavy fermion compounds, occurs at the magnetic field H_m = 97 kOe for H ∥ 〈100〉 at ambient pressure, shifts to lower magnetic fields with increasing pressure P, and becomes zero at the critical pressure P_c ≃ 5:2 GPa. From this experiment, we noted that the metamagnetic transition field H_m is a good tuning parameter to approach the quantum critical point. Correspondingly, the A value of the electrical resistivity ρ = ρ₀ + AT² in the Fermi liquid relation under magnetic field indicates a peak structure at H_m and increases extremely in magnitude from A = 0:29μΩ·cm/K² at ambient pressure to 380μΩ·cm/K² at 5.0 GPa under 0kOe. The present large A value at 5.0 GPa is, however, strongly reduced in magnetic field: 1.45μΩ·cm/K² at 80kOe. It is also noted that the residual resistivity is enhanced at 5.0 and 5.5 GPa, but the enhanced resistivity is strongly reduced in magnetic fields. These results indicate that electronic instability is realized at around P_c ≃ 5.2 GPa.