| Summary: | The anisotropic microwave surface impedance of the high temperature superconductor, YBa₂Cu₃O[sub 7‒δ], has been investigated. Microwave spectroscopy using five microwave cavities has been used to show clearly the development of long lived quasiparticles (QP) in the ab-plane of YBa₂Cu₃O₆.₉₉. Two regimes of transport are found, one below 20 K where the quasiparticle (QP) dynamics is with residual impurities, and above 20 K where umklapp QP-QP interactions dictate the temperature dependence of the transport lifetimes. The c-axis microwave surface impedance of YBa₂Cu₃O₆.₉₅ has been studied into the superconducting state. The long QP lifetimes found in the planes of this material are found to be absent in the conductivity observed along the ĉ-axis, indicating that the confinement of carriers to the planes is an inherent feature of the cuprates. The highly underdoped superconducting state has also been investigated with microwave techniques. The temperature dependence of the ĉ-axis superfluid stiffness is found to scale over a range of hole dopings, corresponding to T[sub c]'s in the range 9-19 K. We further find that the magnitude of the zero temperature c-axis superfluid stiffness grows rapidly with doping, initially as fast as T[sub c]². === Science, Faculty of === Physics and Astronomy, Department of === Graduate
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