Anisotropic Two-Dimensional Screening at the Surface of Black Phosphorus

Abstract

Screening in reduced dimensions has strong consequences on the electronic properties in vander Waals semiconductors, impacting the quasiparticle band gap and exciton binding energy.Screening in these materials is typically treated isotropically, yet black phosphorus exhibits inplane electronic anisotropy seen in its effective mass, carrier mobility, excitonic wavefunctions, and plasmonic dispersion. Here, we use the adsorption of individual potassium atoms on the surface of black phosphorus to vary the near-surface doping over a wide range, while simultaneously probing the dielectric screening via the ordering of the adsorbed atoms. Using scanning tunneling microscopy, we visualize the role of strongly anisotropic screening which leads to the formation of potassium chains with a well-defined orientation and spacing. We quantify the mean interaction potential utilizing statistical methods and find that the dimensionality and anisotropy of the screening is consistent with the presence of a band-bending induced confinement potential near the surface. We corroborate the observed behavior with coverage-dependent studies of the electronic structure with angle-resolved photoemission.

Ultrafast dynamics of the surface photovoltage in potassium-doped black phosphorus

“…There is also a charge redistribution between the valence band (VB) and the conduction band (CB) whose wave functions are respectively pushed to the bulk and confined at the surface of the material [30][31][32][33]. In particular, the CB forms a two-dimensional electrons gas (2DEG) [32,35] and experiences a larger BB, which can be decomposed into the same BB feeled by the VB (φ BB ) and a second one we name Stark potential (φ S ), localized at the extreme surface. At a sufficient coverage, the total CB bending is enough to close the surface band gap but the bulk one remains the same.…”

Unconventional band structure and pseudogap of liquid metals on a crystalline insulator

“…1d), as discussed in Ref. 25,26 . The fast Fourier transform is used to simulate the reciprocal-space lattice structure in Fig.…”

“…A key idea in our experiments is to study the interface between liquid dopants (alkali metals) and a crystalline insulator (black phosphorus) [23][24][25][26] . Black phosphorus is a stack of van-der-Waals layers, in which the honeycomb lattice of P atoms is regularly modulated to form a one-dimensional array of atomic-scale zigzag ridges and valleys (Fig.…”

“…The distribution of alkali-metal atoms on black phosphorus is known to show the oval-shape structure factor (Fig. 1c) at low temperature (above 10 K) 25 . This is the de ning characteristic of liquid (disordered) phases with shortrange order 27,28 , which is clearly distinct from both crystalline and fully random cases (Extended Data Fig.…”

Coulomb decay rates in monolayer doped graphene

“…The important result indicates that the effects due to anisotropic screening and lattice structure play an important role in graphenes and other condensed-matter materials. 46,56,57 Interatomic or intermolecular coulomb decay phenomenon is signicant to chemical bonding in atoms and molecules. A monolayer doped graphene provides an ideal platform to study coulomb decay rate due to graphene.…”