Sharp optical phonon softening close to optimal doping in La$_{2-x}$Ba$_x$CuO$_{4+\delta}$

Matteo d'Astuto (1) , Guy Dhalenne (2) , Jeff Graf (3) , Moritz Hoesch (4) , Paola Giura (1) , Michael Krisch (4) , Patrick Berthet (2) , Alessandra Lanzara (3, 5) , Abhay Shukla (1)

1 IMPMC - Institut de minéralogie et de physique des milieux condensés
2 CHIMSOL - Laboratoire de Physico-Chimie de l'Etat Solide
3 Materials Science Division [LBNL Berkeley]
4 ESRF - European Synchrotron Radiation Facility
5 Department of Physics [Berkeley]

We report a direct observation of a sharp Kohn-like anomaly in the doubly degenerate copper-oxygen bond-stretching phonon mode occurring at $\mathbf{q}\mathrm{=(0.3, 0,0)}$ in La$_{2-x}$Ba$_x$CuO$_{4+\delta}$ with $\mathrm{x=0.14\pm0.01}$, thanks to the high $\mathbf{Q}$ resolution of inelastic x-ray scattering. This anomaly is clearly seen when the inelastic signal is analysed using a single mode but is also consistent with a two mode hypothesis possibly due to a splitting of the degenerate modes due to symmetry breaking stripes. Our observation shows that the effect persists at the stripe propagation vector in a superconducting system close to optimal doping.

Domaines: Electrons fortement corrélés [cond-mat.str-el]

Matteo d'Astuto, Guy Dhalenne, Jeff Graf, Moritz Hoesch, Paola Giura, et al.. Sharp optical phonon softening close to optimal doping in La$_{2-x}$Ba$_x$CuO$_{4+\delta}$. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2008, 78, pp.140511(R). ⟨10.1103/PhysRevB.78.140511⟩. ⟨hal-00311976v3⟩