Transport properties of YBa2Cu3O7-δ /Y0.7Ca0.3Ba2Cu3O7-δ multilayers

• Main Authors: Chun-Li Lin, 林峻立
• Other Authors: Cheng-Chung Chi
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/93420130373868332855

博士 === 國立清華大學 === 物理學系 === 92 === We fabricate [(YBa2Cu3O7-δ)m/(Y0.7Ca0.3Ba2Cu3O7-δ)m]N multilayers with different combinations of (m,N) and study their transport properties in overdoped region under magnetic field. YBa2Cu3O7-δ reaches optimum doping with δ ∼ 0.05, indicating that YBa2Cu3O7-δ system can hardly evolve into overdoped region by merely altering their oxygen content. Replacing Pr3+ with Ca2+ increases one hole of the unit cell where substitution occurs and substantially doping level of 123 system. The decrease of both Tc and resistivity after annealing under 1 atm O2 proves that Y0.7Ca0.3Ba2Cu3O7-δ is overdoped. All the films are deposited by pulse laser deposition with stoichiometric targets. X-ray patterns of those multiplayers do not show any satellite peaks. We measure R-T under magnetic field and Hall effect. Sample 5/5 under magnetic field along a-b plane has smallest broadening of r-T. At room temperature Y0.7Ca0.3Ba2Cu3O7-δ single layer has smallest carrier concentration but largest conductivity. The sign reversal Hall signal of Y0.7Ca0.3Ba2Cu3O7-δ is the hardest to suppress by magnetic field among all the samples. Y0.7Ca0.3Ba2Cu3O7-δ has double sign reversal of Hall coefficient. We conjecture that the Ca diffusion blurs the interfaces between the layers and thus eliminates the satellite peaks. The smallest broadening of sample 5/5 implies that the thickness of 5 unit cell of YBa2Cu3O7-δ layer is longer than twice of the Ca diffusion length. The abnormally small carrier concentration of Y0.7Ca0.3Ba2Cu3O7-δ may be attributed to the coexistence of mobile holes and electrons or the variation of effective mass of holes. We argue that the double sign reversal is due to the inhomogeneous Tc distribution on the film and the temperature error.