BI-209 NMR AND NQR INVESTIGATION OF THE SMALL-GAP SEMICONDUCTOR CE3BI4PT3

We report measurements of the temperature dependence of the Bi2O9 nucl ear quadrupole resonance frequency nu(Q), the Knight shift K, and the spin-lattice relaxation rate 1/T1 in the small-gap semiconductor Ce3Bi 4Pt3 between 1.8 and 300 K. Corresponding measurements also are report ed for the nonmagnetic metallic isomorph La3Bi4Pt3. The nu(Q) data in the Ce compound show a characteristic departure from metallic-to-insul ating behavior when the sample is cooled below T(M) = 80 K, the temper ature of the susceptibility maximum, attributable to a loss of low-fre quency vibrational modes in the insulating state. The Knight shift has both isotropic and axial components; this anisotropy originates from the presence of Ce via a transferred hyperfine coupling between Ce 4f and conduction electrons. An s-f exchange constant greater-than-or-equ al-to 0.4 eV is found, consistent with hybridization in other rare-ear th intermetallic compounds. A change in the scaling between the suscep tibility and both the isotropic and axial Knight shifts at temperature T(M) provides evidence that hybridization between the Ce 4f orbitals and the conduction electrons is responsible for the gap structure. The temperature dependence of the 1/T1 data is consistent with a model el ectronic density of states possessing a temperature-independent pp 8 o f 180 K and a bandwidth of the order of 1600 K. The temperature depend ence of 1/T1 can also be fit well with a temperature-dependent gap wit h delta(0) also almost-equal-to 180 K.