Relation between metamagnetic transition and quantum critical point in heavy fermion compound YbIr₂Zn₂₀

We measured the electrical resistivity in magnetic field H under pressure P for a heavy fermion compound YbIr₂Zn₂₀. The quantum critical point is found to be defined as an electronic state where the metamagnetic transition field H_m becomes zero. This is realized at P_c ≃ 5.2 GPa. The most characteristic feature in the quantum critical pressure region is an anomalously large A value of the electrical resistivity ρ = ρ0 + AT², reaching A 380μΩcm/K ² at 5.0 GPa, which is, however, strongly reduced with increasing the magnetic field: A 1.45μΩcm/K² at 80 kOe. From the result of the de Haas-van Alphen experiment at ambient pressure, the corresponding cyclotron effective mass of conduction electrons at 5.0 GPa is 400 - 500 m ₀ (m₀: rest mass of an electron).