Quantum Criticality And Heavy Fermion State In Ybco2zn20 Under Pressure And Magnetic Field

We studied an effect of pressure on the heavy fermion state of YbCo2Zn20 under magnetic fields. The critical pressure P-c, where the electronic state changes from the heavy fermion state to the antiferromagnetic state, is estimated to be P-c similar or equal to 1.8 GPa. The super-heavy fermion state in the P-c region is found to be strongly destroyed in magnetic fields for H parallel to < 100 >. The field-induced quadrupolar phase, which is most likely realized only for H parallel to < 111 >, is found to be robust even in the antiferromagnetic pressure region.