Anomalous impurity-induced charge modulations in black phosphorus

TL;DR

This study reveals how ionized indium impurities induce localized, anisotropic charge modulations in black phosphorus, demonstrating impurity engineering as a tool to manipulate charge order in 2D semiconductors.

Contribution

It provides direct experimental evidence of impurity-induced charge modulations and challenges existing band-structure interpretations in black phosphorus.

Findings

Charge modulations appear around ionized impurities under STM.

Modulations form a distorted triangular pattern with fixed periodicity.

Charge order exhibits anisotropy opposite to Fermi surface expectations.

Abstract

We observe anomalous charge modulations induced by ionized indium impurities on the surface of the semiconductor black phosphorus by scanning tunneling microscopy (STM). When the impurities are switched into a negatively charged state by the STM tip, periodic charge modulations emerge around the impurity center, but strictly confined by the nanoscale impurity potential. These modulations form a distorted triangular pattern, whose periodicity remains unchanged in a wide range of positive bias. Furthermore, these local charge orders exhibit an anisotropy opposite to that expected based on the anisotropy of the Fermi surface, challenging a simple band-structure interpretation. Our experiment demonstrates the possibility of creating and manipulating macroscopic charge orders through impurity engineering.