Magneto-optical transmission spectroscopy up to 60 T of indirect excitons in the van der Waals semiconductor SnSe

The van der Waals semiconductor SnSe has exceptional thermoelectric properties with a high figure of merit ($ZT$) of 2.6. Extensive research has investigated its ``camel's back'' valence-band structure, which is commonly regarded as an indicator for high thermoelectric performance. However, its interband excitonic properties are not fully understood. Here, we report near-infrared magnetotransmission spectroscopy measurements on SnSe thin films in pulsed magnetic fields B of up to 60 T. They reveal two indirect excitonic absorption processes (in momentum space), associated with the two maxima in the camel's back valence-band structure. The magneto-optical data indicate the presence of interband transitions to the excited $2p$ excitonic states rather than the $1s$ ground state. This observation is consistent with previous first-principles calculation of the electronic structure based on angular momentum and parity-conservation selection rules.