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 system1 such as a crystal consisting of two sublattices2. A potential way to exploit the pseudospin of electrons in pseudospintronics3–5 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 system6,7. 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.
Bibliographical noteFunding Information:
This work was supported by the National Research Foundation (NRF) of Korea (grants nos. 2017R1A2B3011368, 2017R1A5A1014862 and 2018K1A3A7A09027641) and the Future-leading Research Initiative of 2019-22-0079 of Yonsei University. The Advanced Light Source is supported by the US Department of Energy, Office of Sciences, under contract no. DE-AC02-05CH11231. We thank K. Moon, B.-J. Yang, Y.W. Son and J.-W. Rhim for helpful discussions and D.Y. Park for help with experiments.
© 2020, The Author(s), under exclusive licence to Springer Nature Limited.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering