A new ternary family RT2X20 exhibits diverse ground states including quadrupolar order,

heavy-fermion, and superconductivity, which allows us systematic studies on various exotic

phenomena under the identical structure. Among them, all the Yb members YbT2Zn20 are

known to exhibit heavy-fermion ground state[1]. In particular, YbCo2Zn20 has an enormously

large Sommerfeld coefficient 8 J/mol
K2 at ambient pressure, and that can be modied by

relatively small external elds. Whereas pressure induces antiferromagnetic order, magnetic

eld yields metamagnetic transitions at around 0.5 T, and new ordered state in the narrow

region around B∥⟨111⟩ above 6 T [2,3]. In order to get insights into electronic states and its

magnetic eld response, neutron scattering experiments were carried out.

Inelastic neutron scattering experiments on poly-crystalline sample reveal intense low-energy

excitations which consists of quasielastic response and low crystal-eld excitation below 1 meV.

Upon applying eld, quasielastic response was rapidly suppressed while crystal-eld level was

lifted. The result suggests degenerated energy scale between Kondo and crystal-eld interac-

tions in YbCo2Zn20. For B∥⟨111⟩ in the eld-induced ordered phase, we have succeeded to

observe magnetic reections with q=(1/2 1/2 1/2). The induced antiferromagnetic peak ac-

companies characteristic diffuse scattering, and showing complex eld dependence. Nature of

the eld-induced ordered state will be discussed.

[1] M. S. Torikachvili et al., Proc. Natl. Acad. Sci. 104, 9960 (2007).

[2] Y. Saiga et al., J. Phys.: Conf. Ser. 150, 042168 (2009).

[3] M. Ohya et al., J. Phys. Soc. Jpn. 79, 083601 (2010).