Excitons in Magnetic Fields

An applied magnetic field greatly modifies the states and properties of excitons, or bound electron-hole pairs, in photoexcited semiconductors. Depending on the strength of the magnetic field, as well as the density and temperature of the excitons, a variety of physical phenomena occur, providing a rich and controllable environment for not only determining characteristic exciton parameters but also probing complex many-body interactions spectroscopically. In this paper, we review this important sub-field of semiconductor optics. After summarizing the basic theory of excitons in magnetic fields, with a special emphasis on the importance of dimensionality, we describe experimental studies of interband and intraband magneto-optical processes in various semiconductors, including bulk germanium and silicon, III-V semiconductor quantum wells, wires and dots, monolayer transition metal dichalcogenides, and single-wall carbon nanotubes. In addition to linear and continuous-wave optical absorption and photoluminescence spectroscopy studies, we consider nonlinear and ultrafast spectroscopy experiments performed at high magnetic fields. Finally, we discuss recent experiments revealing the extreme stability of two-dimensional excitons against ionization and the cooperative radiative recombination, or superfluorescence, of electron-hole pairs in high magnetic fields.