Black phosphorus as a bipolar pseudospin semiconductor

• Published in: Nature materials Vol. 19; no. 3; pp. 277 - 281
• Main Authors: Jung, Sung Won, Ryu, Sae Hee, Shin, Woo Jong, Sohn, Yeongsup, Huh, Minjae, Koch, Roland J, Jozwiak, Chris, Rotenberg, Eli, Bostwick, Aaron, Kim, Keun Su
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 01.03.2020
• Subjects: Cones; Crystal structure; Crystals; Electron spin; Electrons; Energy; Graphene; Light; Magnetic semiconductors; Phase transitions; Phosphorus; Photoelectrons; Polarization; Room temperature; Semiconductor devices; Spectrum analysis
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/s41563-019-0590-2

Semiconductor devices rely on the charge and spin of electrons, but there is another electronic degree of freedom called pseudospin in a two-level quantum system such as a crystal consisting of two sublattices . A potential way to exploit the pseudospin of electrons in pseudospintronics is to find quantum matter with tunable and sizeable pseudospin polarization. Here, we propose a bipolar pseudospin semiconductor, where the electron and hole states have opposite net pseudospin polarization. We experimentally identify such states in anisotropic honeycomb crystal-black phosphorus. By sublattice interference of photoelectrons, we find bipolar pseudospin polarization greater than 95% that is stable at room temperature. This pseudospin polarization is identified as a consequence of Dirac cones merged in the highly anisotropic honeycomb system . The bipolar pseudospin semiconductor, which is a pseudospin analogue of magnetic semiconductors, is not only interesting in itself, but also might be useful for pseudospintronics.