Pressure-induced lattice instabilities and superconductivity in YBa2Cu4O8 and optimally doped YBa2Cu3O7−δ
M. Calamiotou, A. Gantis, E. Siranidi, D. Lampakis, J. Karpinski, E. Liarokapis
DOI 10.1103/PhysRevB.80.214517 · Physical Review B
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Abstract
Combined synchrotron angle-dispersive powder diffraction and micro-Raman spectroscopy are used to investigate pressure-induced lattice instabilities that are accompanied by superconducting Tc anomalies in YBa2Cu4O8 and optimally doped YBa2Cu3O7−δ, in comparison with the nonsuperconducting PrBa2Cu3O6.92. In the first two superconducting systems there is a clear anomaly and hysteresis in the evolution of the lattice parameters and increasing lattice disorder with pressure, which starts at ≈3.7 GPa. On the contrary, in the Pr compound the lattice parameters follow very well the expected equation of state (EOS) up to 7 GPa. The micro-Raman data of the superconducting compounds show that the energy and width of the Ag phonons exhibit anomalies over the same pressure range where the lattice parameters deviate from the EOS and the average Cu2-Opl bond length exhibits a strong contraction that correlates with the nonlinear pressure dependence of Tc. The anomalous Raman behavior is not observed for the nonsuperconducting Pr compound, clearly indicating a connection with the charge carriers. It appears that the cuprates close to optimal doping are at the edge of lattice instability.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| YBa2Cu4O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 80 | Pressure not reported | unknown |
| YBa2Cu3O7-δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 92 | Pressure not reported | unknown |
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