Abstract
We study the influence of high magnetic fields on the coupled phonon--crystal-field excitation in the high-temperature superconductor ${\mathrm{NdBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ by Raman scattering. With wave functions obtained from inelastic neutron scattering, the Zeeman splitting of the Kramers degenerate crystal-field ground state is evaluated for magnetic fields along the main crystallographic axes. The twofold degeneracy of that excitation, which at zero field was found to couple with a phonon of the same symmetry, is lifted at finite fields. This is used to tune the energy of the crystal-field excitation with respect to that of the phonon. In Raman spectra for magnetic fields up to 16 T we observe broadenings, frequency shifts, and relative intensity changes for the lines of the zero-field doublet. This behavior is in agreement with theoretical predictions for the Zeeman splitting of the crystal-field excitation and the varying phonon content of the coupled wave functions.
Published Version
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