New Materials with Complex Electronic Properties: The Example of Black Phosphorus and its IV-VI Analogues

In this presentation, I will discuss some of our recent results regarding the layered, narrow-gap semiconductor black phosphorus (black-P). The layers of black-P consist of phosphorus six-rings in a so-called chair conformation, and they are weakly bound by van der Waals forces. We have established the detailed high-pressure phase diagram of black-P revealing an anomalous pressure dependence of the superconducting critical temperature and the importance of hole carriers in developing superconductivity. We find that the experimentally observed Tc plateau at high pressure cannot be fully understood with solely considering an electron-phonon mechanism.
We have, furthermore, extended the scope of known black-P IV-VI analogues. We report on the electronic and structural properties of β-GeSe, a previously unreported polymorph of GeSe, with a unique crystal structure that displays strong two-dimensional structural features. Electronic structure calculations suggest that β-GeSe has a bulk band gap of Δ ≈ 0.5 eV, and, in its monolayer form, Δ ≈ 0.9 eV. These values fall right in-between those of α-GeSe and black phosphorus, making it a promising candidate for future applications.