Condensed-Matter Physics Seminar

Synchrotron X-rays diffuse scattering experiments performed at room temperature on a single domain optimally doped crystal of Bi2Sr2CaCu2O8+d (Tc # 91°K) reveal displacive shorter range order or correlations corresponding to a local doubling of the unit cell along the orthorhombic a0 direction. The unit cell used is a0 # 5.4 Å, b0 # 5.4 Å (direction of the modulation b0/qb with qb # 0.21) and c0 30.8 Å. The short range order is therefore perpendicular to the strong long range modulation previously reported and at 45° from the Cu—O—Cu chains, and the at and bt axis used in the tertragonal approximation. The short range order or correlations correspond to planar domains parallel to the conduction plane with an in plane size about 70 Å at room temperature. Experiments at low temperature (37°K) show that this displacive local order is still present with no important change. More recent results as a function of temperature(above room T) and as a function of doping will be presented. A similar diffuse scattering was obtained at room temperature on the one layer compound (Bi2Sr2Cu2O6+d) with a smaller domain size (36Å).