Comment on ‘‘Semimetal-to-semiconductor transition in bismuth thin films’’

In a recent paper, C. A. Hoffman et al. reported field- and temperature-dependent magnetotransport measurements on bismuth thin films and concluded that the semimetal-semiconductor transition in ultrathin films of bismuth, caused by the quantum size effect, was confirmed based on the temperature-dependent behavior of the minority electrons. In this Comment, we discuss the fact that the existing experimental data are not sufficient to establish the picture that the energy overlap of the conduction and valence bands is replaced by an energy gap in sufficiently thin films. Two equally satisfactory pictures are provided for the interpretation of thermal excitations of the minority electrons. The deviation from the equality of electron and hole concentrations in bismuth thin films is also discussed.