On the time reversal in crystals of low point symmetry

Abstract

The problems of additional time reversal degeneracy and the transformation properties of the “time-reversed” wave functions are studied in detail in cases where the low point symmetry (especially the absence of inversion) does not allow, for instance, the use of the formula derived by Elliott (1954). Some special examples are given and misleading statements in the literature are pointed out. The conclusions are summarized so as to be handy in actual applications. Spin is taken into account throughout the whole discussion. Multiplication tables for all double crystallographic point groups can be obtained from the Appendix.