Anisotropic magnetic field dependence of specific heat in the cubic symmetric quadrupolar kondo compound Pr_0.05La_0.95Pb₃

We studied the dependence of the electronic specific heat Cel=T on the magnetic field up to H = 8 T in a dilute quadrupolar compound Pr0.05La0.95Pb3 with a non-Kramers Γ3 doublet in the crystal-electric-field ground state. The magnetic field dependence of Cel/T with -ln T-divergent non-Fermi liquid (NFL) behavior is strongly anisotropic in all three directions of the magnetic field. In H || [100] and [111], the suppression of -ln T dependence appears at T ∼ 0.65 K in H = 4 T and 0.48K in H = 6 T, respectively, whereas in H || [110] it survives at temperatures as low as the lowest temperature, T ∼ 0.2 K. The observed features can be understood by considering the characteristics of the cubic symmetric quadrupolar Kondo effect, which are closely associated with the suppression of the NFL behavior owing to the splitting of the Γ3 doublet, which depends on the direction of the magnetic field, via the Van Vleck process with excited multiplets.