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

Matteo D'Astuto, Guy Dhalenne, Jeff Graf +6

We report a direct observation of a sharp Kohn-like anomaly in the doubly degenerate copper-oxygen bond-stretching phonon mode occurring at $\mathbf{q}=(0.3,0,0)$ in La$_…