Knight Shifts and Band Structure in the Lead-Salt Semiconductors

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The temperature and carrier-concentration dependences of the Pb²⁰⁷ and Te¹²⁵ Knight shifts have been measured in both n- and p-type PbTe. Qualitatively similar data have been reported by others for Pb²⁰⁷ in PbSe. The very large shifts of Pb²⁰⁷ in p-type material and the relatively small shifts of Te¹²⁵ in n-type material are attributed to an s-character contact interaction with the carriers of the valence and conduction bands, respectively. The sign of the isotropic g factor geff is negative in the L-point valence band and positive in the L-point conduction band, in agreement with the results of k·{}p perturbation theory. The temperature dependence of the Knight shift is ascribed to the motion of the Fermi level, the temperature dependence of the energy gap and related band parameters, and to the shift in carriers from the L-point valence band to a second valence band at temperatures above about 200^∘{}K. The localized orbital hyperfine interaction is suggested as the source of the Knight shifts of Pb²⁰⁷ in n-type material and Te¹²⁵ in p-type material.