Electronic band structure of surface-doped black phosphorus

We present an overview on the electronic band structure of surface-doped black phosphorus. Angle-resolved photoemission spectroscopy data show that the in situ deposition of potassium atoms on the surface of single-crystalline black phosphorus modulates the band gap in the wide range of 0.0-0.6 eV. At zero band gap, the surface layers of black phosphorus become a Dirac semimetal whose band dispersion is highly anisotropic, linear in armchair and quadratic in zigzag directions. In light of theoretical band calculations, we elucidate the mechanism of these band modifications as the giant Stark effect due to strong vertical electric fields induced by potassium atoms.