Interband Magneto-Optical Spectroscopy of Pb_1-xSn_xSe

Since the last century, considerable research has been conducted on valley-degenerate narrow gap semiconductors, including Pb_1-xSn_xSe and Pb_1-xSn_xTe alloys. However, it is still not fully understood how differences between the longitudinal valley and the oblique valleys show up in magneto-optical spectroscopy. In this work, we carry out a combined theoretical and experimental work to study this very question. Based on the Mitchell-Wallis model and Kubo formula, we provided a theoretical fit for the interband magneto-optical response of Pb_1-xSn_xSe, which agreed very well with experimental observations and explained the spectral shape of the data at magnetic fields as high as 35T. Our work thus provides a quantitative estimate of the relative strength of the optical absorption from the longitudinal and oblique valleys which can be an important symmetry indicator in future studies.