Necessity of a phase convention for effective g-factors and role of the g-factors in the Knight shifts of PbTe

It is shown that the g-factors which are commonly used to describe the effect of a magnetic field on an electron in a semiconductor are phase-dependent quantities. This difficulty, which is related to the non-tensorial nature of the g-matrix, is fundamental in a Knight shift theory. To solve this problem a phase convention is introduced which allows to define a 'standard representation' between Bloch spinors. This representation yields a common language in which the g-factors are unambiguously defined and permits to assign a physical meaning to the sign of gsub(perpendicular). The importance of the sign of the g-factors is examplified by the surprisingly large ratio of the Knight shifts of 207Pb and 125Te in lead telluride. (author)