Heinz Schmid, Hans Biebuyck, et al.
Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures
A nonzero isotope effect for x=0.15, and an anomalous isotope effect, with the oxygen isotope-effect exponent O larger than the theoretical value of 0.5 for x=0.12, were reported in the past for the La2-xSrxCuO4 system. In view of the importance of understanding the mechanisms of high-temperature superconductivity, a reinvestigation of the isotope effect with more precise materials synthesis and isotope characterization is called for. We synthesized in flowing O218, or in flowing O216, copper-rich and stoichiometric versions of the La2-xSrxCuO4 materials at x=0.125 and x=0.15. We characterized the materials with x-ray diffraction, high-sensitivity, high-temperature mass spectrometry, and magnetic measurements. We found that in the stoichiometric materials, both at x=0.125 and x=0.15, the oxygen isotope-effect exponent, O 0.4. The copper-rich samples at x=0.125 have a larger isotope shift than the stoichiometric ones, due to a larger amount of the La1.67Sr0.33Cu2O5 nonsuperconducting second phase in the containing18 material, than in the containing16 material, which leaves the superconducting phase with a lower strontium concentration, which further lowers Tc. For the copper-rich x=0.15 material we found an oxygen isotope-effect exponent O=0.08. © 1992 The American Physical Society.
Heinz Schmid, Hans Biebuyck, et al.
Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures
A. Gupta, R. Gross, et al.
SPIE Advances in Semiconductors and Superconductors 1990
Biancun Xie, Madhavan Swaminathan, et al.
EMC 2011
Ellen J. Yoffa, David Adler
Physical Review B