dHvA Effect Study of Metamagnetic Transition in CeRu₂Si₂

抄録

The de Haas-van Alphen (dHvA) effect measurements have been performed for both the field ranges above and below the metamagnetic transition field (H_m) in the (010) plane in CeRu₂Si₂. The experimental frequencies and effective masses below H_m agree well with the predictions of the first principle or the renormalized band structure calculations based on the itinerant 4f electron model. On the other hand, those above H_m can be explained well by the localized 4f electron model. The one to one correspondence between the dHvA oscillations below and above H_m can be made. The frequencies are found to change abruptly around H_m. The effective masses decrease considerably around H_m and continue to decrease with increasing field. These observations indicate that the 4f electron nature changes from itinerant to localized around H_m.