PHYSICA[ Physica B 199&200 (1994) 480-482 ELSEVIER Spin-hole doping in the Kondo insulator Ce Bi4Pt3 studied by neutron scattering A. Severing ~, T. Perring b, J.D. Thompson ~'*, P.C. Canfield ¢'d, Z. Fisk ¢ Institute Laue-Langevin, Grenoble, France bRutherford Laboratory, Rutherford, UK CLos Alamos National Laboratm'y, Los Alamos, N M 87545. USA ~ Ames Laboratory, Ames, IA 50011, USA Abstract Inelastic neutron scattering from (Ce~_ ~La~)3Bi4Pta, with x = 0, 0.1 and 0.25, shows that a gap in the spin excitatio~ spectrum decreases monotonically with increasing x and remains well-defined even for x = 0.25. Although the vast majority of heavy-electron com- pounds are metallic at low temperatures, a few are known to have small semiconducting gaps Eg on the order of tens of Kelvins. A simple interpretation tor the origin of Eg is that the bare 4t - or 5f-energy level is renormalized by many-body interactions to be deger, er- ate with a aroad conduction band with which the rener- malized f-level hybridizes. Provided the electron count, including the strongly interacting f-electrons, is exactly two, the lower hybridized band will be filled and the upper band will be empty, leaving an indirect gap from zone boundary to zone center of order V2/W, where V is the hybridization matrix element and W is the conduc- tion bandwidth [1]. An interesting aspect of this model is that, in addition to the existence of a charge gap, there should also be a gap in the spin excitation spectrum [2, 3]. Experimental confirmation of a spin gap has come from inelastic neutron scattering on Ce3Bi4Pt3 [4] and CeNiSn [5]. In both cases the spin and charge gaps are of comparable magnitude and of order 100 and 10 K for the two compounds, respectively. * Corresponding author. When the f-sublattice periodicity is broken by substitu- ting La for Ce in (Cel-xLax)3Bi4Pta a metallic-like resis- tivity develops, the T-linear specific heat coefficient in- creases from near zero to a large value characteristic, of a weakly mixed-valence compound, and a peak at T = Tmax in the static susceptibility moves to lower tem- peratures [6]. Similar trends have also been reported in Cel - xLaxNiSn [7], Sm 1 - xLaxB6 [8] and Yb I - xLuxB12 [9], and are consistent with the presence of Kondo-like interactions. An important question to be answered is how do these small-gap semiconductors evolve into heavy-electron metals with increasing concentrations of nonmagnetic La or Lu. To address this question we have determined the evolution of the spin gap in (Ce: _ ~La,)3Bi~Pt~ by inelastic neutron scattering experi- rnents. Single crystals of (Cet -,LaxlaBi4Pt3 were grown from a Bi flux with nominal La concentrations x = 0, 0.t, 0.25 and 1.0. Electrical resistance and static susceptibility measurements on these crystals followed systematics re- ported previously [6]. Neutron scattering was performed on tt,e H E T spectrometer at the Rutherford spallation source using incident neutron energies Eo of 30 and 0921-4526/94/$07.00 C) 1994 Elsevier Science B.V. All rights reserved SSDI 0921-4526(93)E0364-M