Speaker: Oleg P. Sushkov
Affiliation: School of Physics, Univ. New South Wales
Abstract Details: The phase diagrams of LSCO and YBCO in spite of similarities are remarkably different at low doping. Both the electric conduction properties and the commensurate/incommensurate spin ordering properties differ very significantly. The role of disorder in YBCO is insignificant while the bilayer structure is crucial. On the other hand, in LSCO the intrinsic disorder qualitatively influences the properties of the system. Understanding of reasons for the differences provides an insight into generic physics of an ideal cuprate plane. YBCO is the most important testing ground since it is practically unaffected by disorder. The compound has two magnetic quantum critical points (QCP) located at doping x1=0.06 and x2=0.09. At doping below the QCP1 the compound is a collinear antiferromagnet and also a normal conductor with a finite resistivity at zero temperature. The value of the staggered magnetization at zero temperature is 0.6muB, the maximum value allowed by spin quantum fluctuations. The staggered magnetization is practically independent of doping. At x > x1 the incommensurate spin spiral is developing and simultaneously the static component of the magnetization is quickly decaying with doping. The static magnetization goes to zero at the QCP2. At x > x2 the spin spiral becomes fully dynamic. I overview the bulk of experimental data and describe how these properties are explained and predicted by the theory. The present analysis demonstrates that the superconductivity is related to the spin spiral ordering.Click HERE for directions

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