Lattice instability and soft phonons in single-crystal La2-xSrxCuO4

P. Böni, J. D. Axe, G. Shirane, R. J. Birgeneau, D. R. Gabbe, H. P. Jenssen, M. A. Kastner, C. J. Peters, P. J. Picone, T. R. Thurston

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Abstract

The dispersion of the low-lying phonon branches of several doped and undoped single crystals of La2-xSrxCuO4 has been investigated by using inelastic-neutron-scattering techniques. The zone-center modes are in reasonable agreement with Raman measurements. The reported peaks in the phonon density of states show up at energies that correspond to extrema in the dispersion curves of the transverse and longitudinal acoustic branches near the zone boundary. The tetragonal-to-orthorhombic phase transition is caused by a softening of a transverse-optic-phonon mode at the X point. The rotational nature of the soft mode leads to moderate electron-phonon coupling and the mode is unlikely to enhance significantly conventional phonon mediated superconductivity. We did not observe any evidence for the predicted breathing-mode instability near the zone boundary.

Original languageEnglish
Pages (from-to)185-194
Number of pages10
JournalPhysical Review B
Volume38
Issue number1
DOIs
StatePublished - 1988
Externally publishedYes

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