Spin-hole doping in the Kondo insulator Ce3Bi4Pt3 studied by neutron scattering

摘要

To investigate the effect of non-magnetic impurities on gap formation and stability in Kondo insulators, we have performed inelastic neutron scattering experiments on (Ce(sub 1-x)La(sub x))(sub 3)Bi(sub 4)Pt(sub 3), with x = 0.0, 0 1, 0.25 and 1.0. Data were collected at the Rutherford spallation source using incident neutron energies of 30 and 100 MeV and with the sample temperature fixed at 10K, well below (Delta)g/k(sub B). The gap edge, defined from the rapid onset of scattering intensity, decreases quadratically with La content. However, the energy (Delta)(sub g) at which the magnetic intensity reaches one-half its maximum value scales with x and the temperature T(sub max) at which the static susceptibility is maximum. (Delta)g/k(sub B)T(sub max) is independent of x and equal to 2.5 (plus minus) 0.1, a value curiously close to the total angular momentum of Ce(sup 3+). Three important conclusions are drawn from the these observations: (1) As suggested theoretically, T(sub max) does provide a measure of the gap produced in the spin-excitation spectrum of Kondo insulators. (2) Creation of spin holes by thermal excitation or La substitution has comparable effects on the gap. (3) The existence of a spin gap even with significant perturbation in the Ce-sublattice periodicity suggests that coherence effects are not important for the existence of the gap and that spin dynamics are determined locally.