Antiferromagnetic Parent Compounds Research Articles

Tight-binding parameters and exchange integrals ofBa2Cu3O4Cl2

Band-structure calculations of ${\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{4}{\mathrm{Cl}}_{2}$ within the local-density approximation (LDA) are presented. The investigated compound is similar to the antiferromagnetic parent compounds of the cuprate superconductors but contains additional ${\mathrm{Cu}}_{B}$ atoms in the Cu-O planes. Within the LDA, metallic behavior is found with two bands crossing the Fermi surface. These bands are built mainly from Cu ${3d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and O ${2p}_{x,y}$ orbitals, and a corresponding tight-binding (TB) model for these bands has been parameterized. All orbitals can be subdivided in two sets corresponding to the $A$ and $B$ subsystems, respectively, the coupling between which is found to be small. To describe the experimentally observed antiferromagnetic insulating state, we propose an extended Hubbard model using the parameters derived from the TB fit and local correlation terms characteristic for cuprates. Using this parameter set we calculate the exchange integrals for the ${\mathrm{Cu}\mathrm{}}_{3}{\mathrm{O}}_{4}$ plane, the results being in quite reasonable agreement with the experimental values for the isostructural compound ${\mathrm{Sr}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{4}{\mathrm{Cl}}_{2}$.

Absolute measurements of the high-frequency magnetic dynamics in Hihg- Tc superconductors

We review recent measurements of the high-frequency dynamic magnetic susceptibility in the high- T c superconducting systems La 2− x Sr x CuO 4 and YBa 2Cu 3O 6+ x . Experiments were performed using the chopper spectrometers HET and MARI at the ISIS spallation source. We have placed our measurements on an absolute intensity scale; this allows systematic trends to be seen and comparisons with theory to be made. We find that the insulating S = 1 2 antiferromagnetic parent compounds show a dramatic renormalization of the spin wave intensity. The effect of doping on the response is to cause broadenings in wave vector and large redistributions of spectral weight in the frequency spectrum.

The electronic structure of Ba 2Cu 3O 4Cl 2

Band structure calculations for Ba 2Cu 3O 4Cl 2 within the local density approximation (LDA) have been carried out and the total as well as partial densities of states have been calculated. The investigated compound is similar to the antiferromagnetic parent compounds of cuprate superconductors but contains additional Cu(B) atoms in the planes. Within the LDA metallic behaviour is found with two bands crossing the Fermi level. The result is in disagreement with the experimentally observed antiferromagnetic insulating state, showing the necessity to deal with the electron correlations in a more detailed way. To decide which orbitals should be correlated, a model with Cu-3d and O-2p orbitals was constructed. It is shown that the coupling between the Cu(A) and the additional Cu(B) subsystem is small.