NONLINEAR SUSCEPTIBILITY IN U0.9TH0.1BE13 - DIRECT TEST OF A QUADRUPOLAR KONDO GROUND-STATE

We use nonlinear susceptibility measurements at different fixed temper atures chi(3)(T) as a direct experimental test for magnetism of the U0 .9Th0.1Be13 ground state, where thermodynamic and transport properties were observed recently to be consistent with the quadrupolar two-chan nel Kondo effect. At T < 6 K we found chi(3)(T) dependence, correspond ing to the quadrupolar Kondo ground state. The experimental data may b e understood as due to almost degenerate (for UBe13) and closely situa ted (for U0.9Th0.1Be13) Gamma(3) and Gamma(6) ground-state levels. In the dilute limit (U0.07Th0.93Be13) the ground state of the U-atom is f ound to be nonmagnetic quadrupolar.