Anomalous lattice vibrations of orthorhombic black phosphorus*

Few-layer Black phosphorus (BP) has been extensively studied, over the last years, due to a vast number of peculiar physical properties that are strongly related to its structural anisotropy. While most investigated properties have focused on its electronic and optical properties, there are still some vibrational phenomena, observed experimentally, that are not fully understood from the atomistic point of view.

In this work, we use ab-initio many-body perturbation theory to study the role of electron-phonon coupling on Black phosphorus. Thus, we elucidate the origin of the experimentally observed anomalous band gap temperature dependence and the presence of forbidden vibrational modes at the edges of BP. Our results indicates that the gap temperature dependence is a consequence of the combination of both harmonic and thermal expansion contribution associated to specific low-energy vibrational modes. Accordingly, we relate the presence of forbidden modes at the edges of BP to the atomic rearrangement of phosphorus atoms taking place at the edges.