  The success of black phosphorus in fast electronic and photonic devices is
hindered by its rapid degradation in presence of oxygen. Orthorhombic tin
selenide is a representative of group IV-VI binary compounds that are robust,
isoelectronic, and share the same structure with black phosphorus. We measured
the band structure of SnSe and found highly anisotropic valence bands that form
several valleys having fast dispersion within the layers and negligible
dispersion across. This is exactly the band structure desired for efficient
thermoelectric generation where SnSe has shown a great promise.
