The anisotropic in plain Cu-O strain and the stripe quantum critical point in YBa2Cu3O6+k

Anisotropic Cu-O strain has been measured and a relation between the superconducting critical temperature and the strain is studied in the YBa2Cu3O6+k (Y123). oxygen ordered YBa2Cu3O6+k phases. We show that the critical temperature scales both with the strain along the a axis (s_a,) and along the b axis (s_b). While undoped, the system is close to the critical strain, s_c~ 0.043. The formation of chains with doping gives rise to a decrease of the s_b to take the system away from the critical point approaching the dynamical quantum stripe fluctuations (s_bs_c)