Characteristic heavy fermion properties in YbCuSi and YbTZn (T: Co, Rh, Ir)

Onuki, Yoshichika; Yasui, Shinichi*; Matsushita, Masaki*; Yoshiuchi, Shingo*; Oya, Masahiro*; Hirose, Yusuke*; Dung, N. D.*; Honda, Fuminori*; Takeuchi, Tetsuya*; Settai, Rikio*; Sugiyama, Kiyohiro*; Yamamoto, Etsuji  ; Matsuda, Tatsuma; Haga, Yoshinori   ; Tanaka, Toshiki*; Kubo, Yasunori*; Harima, Hisatomo*

We studied the Fermi surface properties of YbCuSi and YbCuGe with the tetragonal structure by measuring the de Haas-van Alphen (dHvA) oscillations, together with the energy band calculations. It was clarified that 4f electrons contribute to the Fermi surface of a valence fluctuating compound YbCuSi, but not to that of a divalent compound YbCuGe. We also studied the heavy fermion properties of YbTZn (T: Co, Rh, Ir) with the cubic caged structure. The metamagnetic behavior or an abrupt nonlinear increase of magnetization was observed. By measuring the electrical resistivity under pressure and magnetic field, we clarified that the electronic state close to the quantum critical point is realized in YbIrZn at 5.2 GPa and also YbCoZn at ambient pressure.