Infrared optical spectrum of topological crystalline insulator SnTe (001) surface states

We investigate the effects of varying temperature and chemical potential on the optical absorption spectrum of (001) surface states of topological crystalline insulator SnTe using a four-band effective k ⋅ p Hamiltonian. The spectrum is characterized by a narrow peak at 52 meV and a shoulder feature at 160 meV. Both absorptions have maximal intensity at 0 K or when chemical potential is located at the charge neutrality point. Then, as temperature increases or as chemical potential diverges, they both decrease in intensity. The 52 meV peak originates from transitions between high density of states regions surrounding van Hove singularities and is the spectrum’s most prominent feature. Additionally, a third absorption from 110 meV to 150 meV, initially absent at 0 K or chemical potential at charge neutrality point, gradually builds in intensity as temperature increases or as chemical potential diverges. This absorption arises from transitions between low and high energy bands of opposite helicity. Importantly, we find that all distinct spectral features are diminished if the magnitude of chemical potential diverges to values above the van Hove singularity energies. If a given sample’s chemical potential is well-controlled, conventional infrared spectroscopy may be used to identify the spectral signatures of SnTe (001) surface states at room temperatures and without use of large magnetic fields.