First study of the B1g buckling phonon mode in optimally doped, de-twinned, YBa2Cu3O7−δ by inelastic X-ray scattering Original Research Article

We have measured the buckling, B1g, phonon mode of optimally doped, de-twinned, YBa2Cu3O7−δ using inelastic X-ray scattering (IXS) at BL35XU of SPring-8. Measurements of this mode, which has atomic motion transverse to the Cu–O planes, serve to demonstrate some of the advantages of the unique two-dimensional (2-D) analyzer array at BL35. Analysis based on fitting the entire spectra simultaneously at 10 and 100 K shows that the buckling mode is rather broad in the middle of the zone (near (0.3 0 0)). We see a consistent softening of the mode at 10 K as compared to 100 K for all measured wave-vectors (h 0 0), and a q-dependent softening as zone center is approached.