Knight Shifts and Band Structure in Lead Telluride by Helicon-nuclear-spin Interaction

Using the helicon nuclear-spin interaction we have detected NMR in the bulk of lead telluride single crystals. In p-type material, the 207Pb resonance has been studied in detail. The Knight shift of 207Pb in y-type PbTe is strong and negative, indicating a negative g11 value. The gll value at the band edge and the electron density on the Pb site are determined. The wave functions at the valence band edge exhibit a very large s character around the Pb nucleus. Measurements on 12'Te resonance confirm the admitted symmetries for the wave functions at thevalence band edge. Helicon-spin interaction has been used to detect NMR in lead telluride single crystals [I]. The heliconspin interaction is strong for nuclear moments rotating in the same sense as the weakly attenuated helicon wave. This is the case, for example, between nuclei ," 6 . a with positive gyromagnetic ratio and helicons in 0 m p-type material. In lead telluride, the interaction is strong for '07Pb nuclei in p-type PbTe, and IZ5Te n _J in n-type material. On the contrary the interaction is il! LL weak for 207Pb in n-type and for 125Te in p-type PbTe. u We have detected NMR in the four possible situations z o [2] but we restrict the discussioil here to p-type mate4 z rial. The field of resonance of 207Pb in p-type mate2 W rial in shown in figure 1 as a function of concentraa: tion. A very strong negative Knight shift is observed. The hyperfine interaction hamiltonian between an electron i and a nucleus is H extrapolated (C2Hs), Pb-