The interplay of spin, charge and orbital degrees of freedom in compounds with strong correlations results in their rich phase diagrams, where metallic, insulating, superconducting and different types of magnetic orders compete.

Structure of BaVS3

Ground state spin order of BaVS3

One example is BaVS3 which should have quasi-one-dimensional properties according to its structure. It is peculiar that at room temperature (RT), only half of its electrons are delocalized along the V-S octahedra chains, while the other half is already localized and responsible for the Curie-Weiss paramagnetic behavior. Charge degrees of freedom freeze via formation of charge density waves (CDW) below 70 K, while spins order only below 30 K in an antiferromagnetic (AF) structure. With the help of single crystal V L3 edge resonant diffraction measurements we determined precisely the ground state AF order as being incommensurate in three directions, with spins lying in the plane perpendicular to the V-S chains. V L3 edge polarization dependent near-edge X-ray absorption fine structure (NEXAFS) study permitted us, moreover, to observe changes due to the CDW fluctuations below the resistivity minimum.

Structure of Sr14Cu24O41

Dispersion of collective spin excitations in Sr14Cu24O41

The (La,Y)y(Sr,Ca)14-yCu24O41 structure consists of CuO2 chain layers and Cu2O3 ladder planes, separated by Sr,Cu,La,Y atoms. One of their members, Sr14-xCaxCu24O41, with x  11, is the first cuprate superconductor with a non-square lattice. The interplay of spin and charge degrees of freedom is of major importance in cuprate superconductors where the best candidate for the Cooper pair formation mechanism seems to be the spin-fluctuation-glue. We studied collective spin excitations in the parent Sr14Cu24O41 compound by Cu L3 edge RIXS. The amount of mobile charges (holes) is determined by LDA+U calculations of the O K edge polarization dependent NEXAFS spectra. The correlation has here an effect of depleting the ladders and thus decreasing the number of mobile charges, but the amount of holes in superconducting compound is similar to that of high Tc superconductors.

Dernière modification : January 12 2015 17:27:03.