Enhancement of the Superconducting Transition Temperature of MgB2 by a Strain-Induced Bond-Stretching Mode Softening
A. V. Pogrebnyakov, J. M. Redwing, S. Raghavan, V. Vaithyanathan, D. G. Schlom, S. Y. Xu, Qi Li, D. A. Tenne, A. Soukiassian, X. X. Xi, M. D. Johannes, D. Kasinathan, W. E. Pickett, J. S. Wu, J. C. H. Spence
DOI 10.1103/PhysRevLett.93.147006 · Physical Review Letters
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Abstract
We report a systematic increase of the superconducting transition temperature Tc with a biaxial tensile strain in MgB2 films to well beyond the bulk value. The tensile strain increases with the MgB2 film thickness, caused primarily by the coalescence of initially nucleated discrete islands (the Volmer-Weber growth mode.) The Tc increase was observed in epitaxial films on SiC and sapphire substrates, although the Tc values were different for the two substrates due to different lattice parameters and thermal expansion coefficients. We identified, by first-principles calculations, the underlying mechanism for the Tc increase to be the softening of the bond-stretching E2g phonon mode, and we confirmed this conclusion by Raman scattering measurements. The result suggests that the E2g phonon softening is a possible avenue to achieve even higher Tc in MgB2-related material systems.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 41.8 | Pressure not reported | zero_resistance |
| MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 40 | Pressure not reported | unknown |
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