Black phosphorous (BP) is a layered semiconductor with high carrier mobility, anisotropic optical response and wide bandgap tunability. In view of its application in optoelectronic devices, understanding transient photo-induced effects is crucial. Here, we investigate by time- and angle-resolved photoemission spectroscopy BP in its pristine state and in the presence of Stark splitting, chemically induced by Cs ad-sorption. We show that photo-injected carriers trigger bandgap renormalization and a concurrent valence band attening caused by Pauli blocking. In the biased sample, photoexcitation leads to a long-lived (ns) surface photovoltage of few hundreds mV that counterbalances the Cs-induced surface band bending. This allows us to disentangle bulk from surface electronic states and to clarify the mechanism underlying the band inversion observed in bulk samples.
@article{arxiv.2007.09754,
title = {Non-equilibrium Band Broadening, Gap Renormalization and Band Inversion in Black Phosphorus},
author = {H. Hedayat and A. Ceraso and G. Soavi and S. Akhavan and A. Cadore and C. Dallera and G. Cerullo and A. C. Ferrari and E. Carpene},
journal= {arXiv preprint arXiv:2007.09754},
year = {2022}
}