We present here a study on the influence of the oxygen reduction process on the structural and transport properties of epitaxial thin films of the electron-doped cuprate Nd2−xCexCuO4±δ. As is well known, the gradual removal from as-grown samples of a tiny percentage of excess oxygen ions leads to a drastic improvement of the metallic character of this system, which eventually becomes superconducting for suitable values of the cerium concentration, with amaximal critical temperature Tc≃25 K. We find that the oxygen loss occurring in thermal treatments in the temperature range 500–850 °C leads to a reduction of the disorder hindering conductance processes, but is insufficient to make the system become superconducting. On the other hand, as soon as the annealing temperature is raised above 850 °C, superconductivity appears, and at the same time a systematic variation of the length of the unit cell along the c-axis direction is detected. This is a clear indication that the transition to the superconducting phase is always accompanied by a structuralmodification. A further salient feature characterizing samples annealed at high temperatures is the emergence of a linear contribution in the normalstate resistivity, which superimposes to the quadratic one already present in samples which are oxygenreduced below 850 °C. This contribution is probably associated with the formation of hole-like carriers located at hole pockets developing at the Fermi energy along the nodal direction in the Brillouin zone. We conjecture that the evolution of the electronic stateswith oxygen removal for a given ceriumconcentration close to optimal doping, is similar to the one taking place in optimally annealed samples where cerium concentration is raised from the underdoped to the lightly overdoped regime value.

Correlation between structural and transport properties in epitaxial films of Nd2−xCexCuO4±δ

GUARINO, ANITA;ROMANO, Alfonso;NIGRO, Angela
2012

Abstract

We present here a study on the influence of the oxygen reduction process on the structural and transport properties of epitaxial thin films of the electron-doped cuprate Nd2−xCexCuO4±δ. As is well known, the gradual removal from as-grown samples of a tiny percentage of excess oxygen ions leads to a drastic improvement of the metallic character of this system, which eventually becomes superconducting for suitable values of the cerium concentration, with amaximal critical temperature Tc≃25 K. We find that the oxygen loss occurring in thermal treatments in the temperature range 500–850 °C leads to a reduction of the disorder hindering conductance processes, but is insufficient to make the system become superconducting. On the other hand, as soon as the annealing temperature is raised above 850 °C, superconductivity appears, and at the same time a systematic variation of the length of the unit cell along the c-axis direction is detected. This is a clear indication that the transition to the superconducting phase is always accompanied by a structuralmodification. A further salient feature characterizing samples annealed at high temperatures is the emergence of a linear contribution in the normalstate resistivity, which superimposes to the quadratic one already present in samples which are oxygenreduced below 850 °C. This contribution is probably associated with the formation of hole-like carriers located at hole pockets developing at the Fermi energy along the nodal direction in the Brillouin zone. We conjecture that the evolution of the electronic stateswith oxygen removal for a given ceriumconcentration close to optimal doping, is similar to the one taking place in optimally annealed samples where cerium concentration is raised from the underdoped to the lightly overdoped regime value.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11386/3906569
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