Negative Oxygen Isotope Effect on the Static Spin Stripe Order in La$_{2-x}$Ba$_{x}$CuO$_{4}$ ($x$ = 1/8)

Cuprate high temperature superconductors (HTS's) are characterized by a complex interplay between lattice, charge, and spin degrees of freedom. One of the remarkable phases is a self-organized charge/spin structure, which is known as ''stripes'' and is observed in some cuprates near 1/8 doping. The microscopic origin of the stripe phase is still unclear at present. We report large negative oxygen-isotope ($^{16}$O/$^{18}$O) effects (OIE's) on the static spin-stripe ordering temperature $T_{\rm so}$ and the magnetic volume fraction $V_{\rm m}$ in La$_{2-x}$Ba$_{x}$CuO$_{4}$ ($x$ = 1/8) observed by means of muon spin rotation experiments [1]. The corresponding OIE exponents were found to be $\alpha_{T_{\rm so}}$ = -0.57(6) and $\alpha_{V_{\rm m}}$ = -0.71(9), which are sign reversed to $\alpha_{T_{\rm c}}$ = 0.46(6) measured for the superconducting transition temperature $T_{\rm c}$. This indicates that the electron-lattice interaction is involved in the stripe formation and plays an important role in the competition between bulk superconductivity and static stripe order in the cuprates. [1] Z. Guguchia et. al., Phys. Rev. Lett. 113, 057002 (2014).