UBC Theses and Dissertations
Precision Measurements of Magnetic Penetration Depth in Precision Measurements of Magnetic Penetration Depth in YB[sub a]₂Cu₃0₇₋[sub δ] Kamal, Saeid
Using sensitive cavity perturbation techniques, we have performed extensive measurements of the microwave surface impedance of high quality single crystals of YB[sub a]₂Cu₃0₇₋[sub δ]. We have employed a novel loop-gap resonator with operating frequency at about 1 GHz and quality factor of 1 x 10⁶ to 4 x 10⁶ to probe the electrodynamics of the superconducting state of YB[sub a]₂Cu₃0₇₋[sub δ]. The main focus of the thesis has been on the precision measurements of the magnetic penetration depth. We have studied the superconducting region of the phase diagram of YB[sub a]₂Cu₃0₇₋[sub δ] by measuring single crystals with various amounts of oxygen doping, ranging from underdoped ortho-II phase (δ = 0.5) to the fully oxygenated (δ = 0; slightly overdoped). The role of impurities have been studied by introducing controlled amounts of Zn, Ni, and Ca impurities into the crystals. A new generation of ultra high purity single crystals were grown at UBC using BaZrOa crucibles. Observation of extremely long quasiparticle scattering times in these higher purity crystals opened a new chapter in microwave spectroscopy of quasiparticles in YB[sub a]₂Cu₃0₇₋[sub δ] at our laboratory. Measurements of magnetic penetration depth performed in this thesis have been a continuous contributing factor to these studies. Also careful measurements of magnetic penetration depth near the transition temperature T[sub c]₁, has revealed non-mean field behaviour consistent with 3D-XY critical fluctuations.
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