Figure 1

(Color online) Energy per formula unit vs $c/a$ for tetragonally distorted CuO, in-plane lattice constant $a=3.905\text{Å}$. The energy zero is the lowest structure, AF-II at $c/a=1.09$. In the regions labeled “$z^2$” and “$x^2-y^2$,” the magnetic hole has $d_{z^2}$ and $d_{x^2-y^2}$ character respectively. The barrier between the two minima corresponds to degenerate $e_g$ states.Reuse & Permissions

Figure 2

Density of states of CuO projected on $\text{Cu}{e}_g$ orbitals at the axially expanded minimum. Energy zero is the valence-band top. Thick solid line: $d_{x^2-y^2}$; thin solid line, shaded curve: $d_{z^2}$. The antiferromagnetically split Cu hole is almost pure $d_{x^2-y^2}$. The spin splitting of this state, 9.5 eV, is a measure of the effective on-site interaction $U$.Reuse & Permissions

Figure 3

Density of states of CuO projected on $\text{Cu}{e}_g$ orbitals at the axially compressed minimum. Energy zero is the valence-band top. Thick solid line: $d_{x^2-y^2}$; thin solid line, shaded curve: $d_{z^2}$. The antiferromagnetically split Cu hole is almost pure $d_{z^2}$. The spin splitting is similar to that in Fig. 2.Reuse & Permissions

Figure 4

(Color online) Schematic basal $\left(xy\right)$-plane view of the AF-II (or equivalently AF-4) structure. Filled and empty symbols indicate up or down spin. Square and circles are Cu atoms belonging to the two cubic AF sublattices discussed in the text. The intra sublattice AF coupling is named $J_{\parallel }$ and the intersublattice coupling is named $J_{d\parallel }$. Note that the apparent frustration is avoided in this structure because the contributions involving $J_{d\parallel }$ cancel. The vertical $xz$ plane is obviously equivalent upon exchange of $\parallel$ by $\perp$, and allowance for the different numerical value of the J’s. Oxygens (not drawn) sit at the crossings of the two nets.Reuse & Permissions

Figure 5

(Color online) Top: stacking sequence of the AF-II (right) and AF-4 structures (left) viewed in the vertical (010) plane the $c$ axis being (001)). Bottom: alternate view of AF-II (right) and AF-4 (left) as, respectively, (111)-oriented monolayer and (110)-oriented bilayer AF-A structures. Filled and empty symbols are up and down Cu’s. Oxygens are not shown.Reuse & Permissions

Figure 6

Valence density of states compared with UPS peak positions. The DOS is broadened by a running average procedure.Reuse & Permissions