Knowledge Bank

The transport symmetry is a generalization of the interchange symmetry discussed in the 1965 and 1966 symposia. It is the minimal symmetry establishing the physical equivalence among a set of constituents (atoms, molecules) throughout the crystal. Essentially it is a combination of an interchange symmetry (establishing the equivalence within one unit cell) and the translational symmetry. Like the interchange symmetry the transport symmetry is expected to be useful for the classification of eigenstates and the interpretation of spectroscopic data of crystals. The specific aspect prompting this work is the spectroscopic investigation of $k\ne 0$ states in molecular crystals: selection rules related to band-band transitions and the spectroscopic observation of complete exciton k-band structures.