Electronic correlation-driven orbital polarization transitions in the orbital-selective Mott compound Ba2CuO4−δ

The electronic states near the Fermi level of recently discovered superconductor ${\mathrm{Ba}}₂{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$ consist primarily of the Cu ${d}_{{x}²\ensuremath{-}{y}²}$ and ${d}_{3{z}²\ensuremath{-}{r}²}$ orbitals. We investigate the electronic correlation effect and the orbital polarization of an effective two-orbital Hubbard model mimicking the low-energy physics of ${\mathrm{Ba}}₂{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$ in the hole-rich regime by utilizing the dynamical mean-field theory with the Lanczos method as the impurity solver. We find that the hole-overdoped ${\mathrm{Ba}}₂{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$ with $3{d}⁸$ (${\mathrm{Cu}}³⁺$) is in the orbital-selective Mott phase (OSMP) at half-filling, and the typical two-orbital feature remains in ${\mathrm{Ba}}₂{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$ when the electron filling approaches ${n}_e\ensuremath{\sim}2.5$, which closely approximates to the experimental hole doping for the emergence of the high-${T}_c$ superconductivity. We also obtain that the orbital polarization is very stable in the OSMP, and the multiorbital correlation can drive orbital polarization transitions. These results indicate that in hole-overdoped ${\mathrm{Ba}}₂{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$ the OSMP physics and orbital polarization, local magnetic moment, and spin or orbital fluctuations still exist. We propose that our present results are also applicable to ${\mathrm{Sr}}₂{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$ and other two-orbital cuprates, demanding an unconventional multiorbital superconducting scenario in hole-overdoped high-${T}_c$ cuprates.