Linear scanning tunneling spectroscopy over a large energy range in black phosphorus

Abstract

We reveal the unique electronic characteristics of the conduction band (CB) of black phosphorus (BP) by combining low-temperature scanning tunneling microscopy/spectroscopy (STM/STS), density functional theory calculations, analytic fitting, and model simulations. We discover that the differential conductance spectrum, which represents the local density of states (LDOS) of BP, exhibits a linear character over a large energy range in the unoccupied electronic state region. Combining theoretical calculations, we demonstrate that the linear character right above the conduction band minimum originates from a specific combination of the anisotropic band dispersions of BP's CB. In particular, the wave function of BP's CB possesses a pronounced density between BP layers and extends into the vacuum significantly, which is in sharp contrast to those of adjacent bands. This makes the CB dominate STS signals even when the energy is sufficiently high to involve other bands, and maintains the linearity of the STS spectrum over a wide energy range. The fact that the CB provides linear DOS and possesses pronounced wave function density in BP interlayers provides new insights for engineering the electronic structures and properties of BP and BP based materials.