Ground State Of CuO Research Articles

Effective orbital symmetry of CuO: Examination by nonresonant inelastic x-ray scattering

We report on measurements of nonresonant inelastic x-ray scattering (NIXS) to unravel the effective symmetry of Cu $3d$ orbitals in the ground state of CuO. A clear feature of energy loss at about 2 eV exists in the NIXS spectrum, arising from $dd$ excitations; the intensities of these excitations display a pronounced anisotropy. The comparison between the measured angular distributions of scattering and those from theoretical predictions by the tesseral harmonics indicates that, in terms of a hole picture, the lowest-energy $dd$ excitation is the orbital transition ${x}^{2}\ensuremath{-}{y}^{2}$ $\ensuremath{\rightarrow}$ $xy$. In addition, the transition ${x}^{2}\ensuremath{-}{y}^{2}$ $\ensuremath{\rightarrow}$ $3{z}^{2}\ensuremath{-}{r}^{2}$ has an energy higher than ${x}^{2}\ensuremath{-}{y}^{2}$ $\ensuremath{\rightarrow}$ $yz/zx$, in contrast to a previous interpretation. Our results imply a large Jahn-Teller-like splitting between ${x}^{2}\ensuremath{-}{y}^{2}$ and $3{z}^{2}\ensuremath{-}{r}^{2}$ orbitals. The theory assuming a ${C}_{4h}$ symmetry explains the angular dependence of the NIXS spectra fairly well, implying that this symmetry is a reasonable approximation. This demonstrates that NIXS can provide important information for modeling of the electronic structure of $d$ ions embedded in a complicated crystal field.

Magnetic and electronic properties of Cu1−xFexO from first principles calculations

Magnetic and electronic properties of Cu1−xFexO systems with x = 6.25% and 12.5% have been investigated using first principles calculations. The ground state of CuO is an antiferromagnetic insulator. At x = 6.25%, Cu1−xFexO systems with Fe on 2 and 4 substitution positions are half-metallic due to the strong hybridization among Fe, the nearest O and Cu atoms, which may come from the double exchange coupling between Fe2+–O2−–Cu2+. At x = 12.5%, Cu1−xFexO system with Fe on 9–11 position has a strong spin polarization near the Fermi level and the system energy is lowest when the doped two Fe atoms form ferromagnetic configuration. This indicates the two doped Fe atoms prefer to form ferromagnetic configuration in Fe2+–O2−–Cu2+–O2−–Fe2+ chains. While in the Fe on 7–11 position, the spin-down Fe–11 3d states have a large spin polarization near the Fermi level when the two doped Fe atoms form antiferromagnetic configuration. It is concluded that the transition metal doping can modify the magnetism and electronic structures of Cu1−xFexO systems.

Theoretical study of low-lying electronic states of CuO and CuO −

Abstract: DFT (B3LYP) calculations on the spectroscopic properties of the low-lying states of CuO and CuO − have been carried out. The corresponding electronic spectrum has been estimated by using MRSDCI, MP4(SDQ) and CCSD(T) methods. The results support the assignment, based on the recent photoelectron spectroscopic (PES) experiment that the state at 1.91 eV is a CuO( 4 Σ − ) and the CuO( 2 Δ) arising from the electron detachment of a 3d electron of CuO − is more than 2.2 eV above the ground state of CuO(X 2 Π ). Our calculations suggest that the feature a′ in the PES experiment of CuO − should be due to the 1 1 Π excited state, rather than due to the spin-orbit splitting component of the 1 3 Π state as suggested in the PES experiment.

Theory of the Normal State Hall Effect in Copper Oxide Superconductors

The anomalous behavior of the Hall effect in the normal state of La 2- x Sr x CuO 4 is investigated theoretically based on the recently calculated results that 3 B 1 g is the ground state of CuO 6 cluster in La 2- x Sr x CuO 4 for x >0.1. Fitting the transfer interaction of 3 B 1 g cluster in La 2- x Sr x CuO 4 to the a 1 g * band in the LDA band structure, we first note that the band width of a 1 g * band, about 0.8 eV, is much smaller than the Hubbard U interaction between a * 1 g holes. Then the x -dependence of the Hall coefficient is calculated within the Hubbard I approximation for T =0 K. The calculated results show that, (1) the Hall coefficient at T =0 K behaves inversely as x in the low Sr concentration region up to x ∼0.05, (2) it deviates downwards from 1/ x in the region above x ∼0.05, and (3) it changes the sign from positive to negative at x =0.42. Anomalous temperature dependence is also discussed.

1A1gto3B1gConversion at the Onset of Superconductivity in La2-xSrxCuO4Due to the Apical Oxygen Effect

By the first-principles variational calculations we show that, with the increase of Sr concentration, the ground state of CuO 6 octahedron in La 2- x Sr x CuO 4 changes from 1 A 1 g to 3 B 1 g near the observed onset concentration of superconductivity while the ground state of the CuO 4 cluster in Nd 2- x Ce x CuO 4 is always 3 B 1 g in the presence of dopant electrons. Based on this result, two kinds of phase diagrams are predicted for hole- and electron-doped superconductors. These results support the spin polaron mechanism proposed by Kamimura et al .