Characteristic Heavy Fermion Properties in YbCu2Si2and YbT2Zn20(T: Co, Rh, Ir)

Abstract

We studied the Fermi surface properties of YbCu 2 Si 2 and YbCu 2 Ge 2 with the tetragonal structure by measuring the de Haas–van Alphen (dHvA) oscillations, together with the energy band calculations. It was clarified that 4 f electrons contribute to the Fermi surface of a valence fluctuating compound YbCu 2 Si 2 , but not to that of a divalent compound YbCu 2 Ge 2 . Namely, the Fermi surface of YbCu 2 Si 2 contains the 4 f -components considerably and the corresponding cyclotron effective mass m c * of the main Fermi surface is large, m c * =30–40 m 0 ( m 0 : rest mass of an electron). We also studied the heavy fermion properties of YbT 2 Zn 20 (T: Co, Rh, Ir) with the cubic caged structure. The metamagnetic behavior or an abrupt nonlinear increase of magnetization was observed at 6 kOe in YbCo 2 Zn 20 , 63 kOe in YbRh 2 Zn 20 , and 97 kOe in YbIr 2 Zn 20 for H ∥ , which was measured at 60 mK in YbCo 2 Zn 20 and 1.3 K in YbRh 2 Zn 20 and YbIr 2 Zn 20 . The metamagnetic field is found to be a good pa...