  Superconducting (SC) gap symmetry and magnetic response of cubic
U0.97Th0.03Be13 are studied by means of high-precision heat-capacity and dc
magnetization measurements using a single crystal, in order to address the
long-standing question of its second phase transition at Tc2 in the SC state
below Tc1. The absence (presence) of an anomaly at Tc2 in the field-cooling
(zero-field-cooling) magnetization indicates that this transition is between
two different SC states. There is a qualitative difference in the field
variation of the transition temperatures; Tc2(H) is isotropic whereas Tc1(H)
exhibits a weak anisotropy between [001] and [111] directions. In the low
temperature phase below Tc2(H), the angle-resolved heat-capacity $C(T,H, \phi)$
reveals that the gap is fully opened over the Fermi surface, narrowing down the
possible gap symmetry.

Superconductivity;Strongly Correlated Electrons