The authors derive a solution for the density matrix of an electron moving in a spatially periodic field. The solution corresponds to a mixed state of the system.
PACS:03.65.−w DOI:10.1070/PU1990v033n12ABEH002668 URL: https://ufn.ru/en/articles/1990/12/e/ Citation: Vardanyan G A, Mkrtchyan G S "A solution to the density matrix equation" Sov. Phys. Usp.33 (12) 1072–1072 (1990)