Different phase leads to different transport behavior in Pb₉Cu(PO₄)₆O compounds

The recent claimed room-temperature superconductivity in Cu-doped lead apatite at ambient pressure is under debate. To identify its physical origin, we conducted a detailed analysis of the crystal structure, band structure, lattice dynamics and magnetic properties of the parent Pb[Formula: see text](PO 4 ) 6 O compound and the two different phases of Pb 9 Cu(PO 4 ) 6 O (LK-99) compound. Our results show that the parent Pb[Formula: see text](PO 4 ) 6 O compound is an indirect band gap semiconductor, where Cu doping at the 4f site of Pb leads to a semiconducting to half-metallic transition. Two half-filled flat bands spanning the Fermi energy levels are present in the 4f phase of LK-99, which are mainly formed by hybridization of the d orbitals of Cu with the 2p orbitals of O. In addition, 6h phase of LK-99 always has spin polarization at the bottom of the conduction band and at the top of the valence band, making the material a magnetic semiconductor. Our theoretical research reveals recent experimental reports on the different transport properties of LK-99.