Novel Electronic States of Heavy Fermion Compound YbCo^sub 2^Zn^sub 20

We studied the heavy fermion compound YbCo...Zn... with an electronic specific heat coefficient ... \( \simeq \) 8000 mJ/(K...-mol) by measuring the de Haas-van Alphen (dHvA) oscillation, Hall effect, magnetic susceptibility, and magnetization at ambient pressure, as well as the electrical resistivity in magnetic fields of up to 320 kOe and at pressures of up to 5 GPa. The detected Fermi surfaces are small in volume, reflecting the small Brillouin zone based on the large cubic lattice constant a = 14.005 ... The cyclotron effective masses, which were determined from the dHvA experiment, are found to be markedly reduced in magnetic fields. In other words, the detected cyclotron masses of 2.2-8.9 m0 (m...: the rest mass of an electron) at H... = 117 kOe are enhanced to 100-500 m... at 0 kOe. By applying pressure, the heavy fermion state disappears at P... \( \simeq \) 1.8 GPa and orders antiferromagnetically for P > P... The field-induced antiferroquadrupolar phase, which is observed only for \(H\parallel \langle 111\rangle \) in the magnetic field range from H... = 60 kOe to \(H'_{\text{Q}} = 210\) kOe, is found to shift to lower magnetic fields and merge with the antiferromagnetic phase at 4.5 GPa. (ProQuest: ... denotes formulae/symbols omitted.)