Coupled electron-crystal lattice symmetry reduction in insulating materials with transition metal dopants: Cu-doped Pb_10(PO_4)_6O, and Vanadium doped SrTiO_3
arXiv (Cornell University)(2023)
摘要
We study two materials and clarify the mechanisms at play in stabilizing an
insulating state, and an impurity level in the bandgap using ab initio
calculations: Cu-doped Pb_10(PO_4)_6O ('LK-99') and V-doped SrTiO_3,
both transition metal-doped insulators. In both cases, the electron degeneracy
and crystal lattice symmetry are broken, leading to an insulating state, and a
magnetically and orbitally polarized impurity state within the bulk gap,
clearly separated from the doped material's valence and conduction bands.
Doping slightly lowers the band gap of the bulk materials, with possible
applications related to bandgap tuning (e.g. photocatalysis). We also resolve
previously noticed inconsistencies between density functional theory results
and experiment regarding doping site energetics, crystal structure, and
transparency in Cu-doped phosphate lead apatite 'LK-99'. Doping one of each
type of site in the same unit cell (20 % doping) leads to two spin-polarized
impurity bands in the material's gap. The local transition metal ion sites may
behave like color centers (or f-centers), possibly giving color at low
temperatures to what we predict to be a transparent, insulating material in the
recently synthesized LK-99 at low temperatures. The results shown here likely
exclude superconductivity by known mechanisms. We also note the potential of
this type of doping to lead to altermagnetism - though the Cu-doped lead
apatite does not seem particularly promising in this regard. Throughout this
paper, we also discuss tools that can be used to quickly understand the local
d-orbital symmetry of the impurity, and the coupling between the crystal
structure and the impurity electronic order on the d-shell.
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关键词
pb$_{10}$po$_4$$_6$o,cu-doped,electron-crystal
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