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SUPERSTRIPES NEWS - a digital publication

Superconductivity under extreme conditions:
an analogy between Li and Cuprates

The superconductivity under extreme conditions (very high pressure) seems to have a close analogy inspite of differences in the materials structure.
Recently two reports [1,2] open a new way to look at the problem of the relationship between the structure and superconductivity. Indeed the high external pressure pushes lithium towards low symmetry structures like the internal pressure on the copper oxide plane in perovskites [3]. In Lithium the superconducting transition (lower than 4 milliKelvin at zero pressure) goes up to 23 K under high pressure . The results enlighten the role of pressure and low symmetry structures for understanding the high Tc superconductivity in cuprates. In fact the electronically active CuO2 plane is under very high internal pressure due to lattice mismatch or misfit [3]. The internal compressive pressure brings the CuO2 plane towards low symmetry structures, up to a critical pressure of about 30 Gpa (~8% microstrain, or internal strain, on the CuO2 bonds, )

1. K Shimizu et al. Nature 419 (2002) 597.
2. V. V. Struzhkin, et al Science. 298 (2002) 1213.
3. A. Bianconi et al,J. Phys. Cond.Mat. 12, 10655 (2000)

The superconducting Tc in lithium under pressure mesured by V.V.Struzhkin as a function of the external pressure normalized to the critical pressure (83 GPa)

The superconducting Tc in cuprates as a function of the internal pressure due to lattice mismatch and proportional to the Cu-O microstrain normalized to the upper critical pressure (~30 GPa) or microstrain ~8% [ref.3]

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