209Bi NMR and NQR investigation of the small-gap semiconductor Ce3Bi4Pt3.

A P Reyes,P C Canfield,Z Fisk,J D Thompson,R H Heffner

doi:10.1103/physrevb.49.16321

A P Reyes, P C Canfield + Show 3 more

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https://doi.org/10.1103/physrevb.49.16321

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Abstract

209Bi NMR and NQR investigation of the small-gap semiconductor Ce3Bi4Pt3.

Highlights

The compound Ce3Bi4Pt3 is one of about a dozen small-gap semiconducting compounds involving either rare-earth or actinide metals. ' Most of these semiconductors possess a cubic strucf ture, and the behavior of their lattice parameters suggests a mixed-valence state for the electrons
This behavior is characteristic of dense Kondo systems, where the reduction in the susceptibility at low temperatures is produced by the hybridization of the local moments with the conduction electrons
The measurements of the temperature dependence of v& show a dramatic change in the electric field gradient (EFG) at a nuclear site as the material goes from an insulating to a conducting state. (Previous boron NMR measurements on YbB&2 and SmB6 were unable to resolve a quadrupole splitting because of the small boron quadrupole moment. )

Summary

15 JUNE 1994-I

Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (Received 14 February 1994). We report measurements of the temperature dependence of the Bi nuclear quadrupole resonance frequency v&, the Knight shift K, and the spin-lattice relaxation rate 1/Tl in the small-gap semiconductor Ce3Bi4Pt3 between 1.8 and 300 K. The v& data in the Ce compound show a characteristic departure from metallic-to-insulating behavior when the sample is cooled below TM =80 K, the temperature of the susceptibility maximum, attributable to a loss of low-frequency vibrational modes in the insulating state. A change in the scaling between the susceptibility and both the isotropic and axial Knight shifts at temperature T~ 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/Tl data is consistent with a model electronic density of states possessing a temperature-independent gap 5 of 180 K and a bandwidth of the order of 1600 K.

INTRODUCTION

SAMPLE PREPARATION

The total Hamiltonian for nuclear spin in magnetic

Nuclear quadrupole resonance

Spin-lattice relaxation rates

CONCLUDING REMARKS