Semiconductivity induced by spin–orbit coupling in Pb9Cu(PO4)6O

Recently, a possible room-temperature superconductor known as LK-99 (Pb10-xCux(PO4)6O (0.9 < x < 1.1)) has sparked a wave of research. However, many experimental works have proven that it is a semiconductor. At the same time, many theoretical works have reached the conclusion that it is a flat band metal. The inconsistency between theoretical and experimental works may be caused by neglecting the spin–orbit coupling effect in calculations. We performed calculations of electronic structure of Pb9Cu(PO4)6O with spin–orbit coupling, and the results show that it's indeed a semiconductor, not a metal. In the ferromagnetic state it is an indirect-bandgap semiconductor with a bandgap of 292 meV. While in the antiferromagnetic-A state, it is a direct-bandgap semiconductor with a bandgap of 300 meV. Our work provides a possible explanation for the contradictions of previous experiments and theories, and provides some theoretical basis for the potential application of Pb9Cu(PO4)6O as a semiconductor.