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Oxygen Isotope Effect and Structural Phase Transitions in La2CuO4-Based Superconductors
Science (New York, N.Y.)
|December 7, 1990
Summary
The oxygen isotope effect in cuprate superconductors is strongly linked to structural phase transitions. This suggests electronic contributions to lattice instability are key to superconductivity in these materials.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Solid State Chemistry
Background:
- The superconducting transition temperature (Tc) in cuprates is sensitive to isotopic composition.
- The oxygen isotope effect (alpha(o)) provides insights into the pairing mechanism in superconductors.
Purpose of the Study:
- Investigate the doping dependence of the oxygen isotope effect in La2-xSrxCuO(4) and La2-xBaxCuO(4).
- Explore the relationship between the isotope effect, structural phase transitions, and superconductivity in these materials.
Main Methods:
- Systematic variation of strontium (Sr) and barium (Ba) doping (x) in La2-x(Sr,Ba)xCuO(4).
- Measurement of the oxygen isotope effect (alpha(o)) on the superconducting transition temperature.
- Synchrotron X-ray diffraction to analyze structural parameters and phase transitions.
Main Results:
- Maximum alpha(o) values (> 0.5) observed near x = 0.12 in both Sr- and Ba-doped compounds.
- Little change in lattice parameters or orthorhombicity with isotope exchange in high alpha(o) materials.
- Correlation between anomalous alpha(o) behavior, structural phase transitions (Abm to P4(2)/ncm), and doping levels.
Conclusions:
- The isotope effect's unusual doping dependence is linked to proximity to structural phase transitions.
- Static structural distortions do not cause the large isotope effects observed.
- An electronic contribution to lattice instability, peaking at ~1/8 hole per Cu atom, is implicated.
- A strong connection exists between hole doping, CuO(6) octahedra tilting instabilities, and superconductivity in La(2)CuO(4)-based systems.
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