Negative Oxygen Isotope Effect on the Static Spin Stripe Order in Superconducting ${\mathrm{La}}_{2-x}{\mathrm{Ba}}_x{\mathrm{CuO}}_4(x=1/8)$ Observed by Muon-Spin Rotation

Large negative oxygen-isotope (${}^{16}\mathrm{O}\mathrm{and}{}^{18}\mathrm{O}$) effects (OIEs) on the static spin-stripe-ordering temperature $T_{\text{so}}$ and the magnetic volume fraction $V_{\mathrm{m}}$ were observed in ${\mathrm{La}}_{2-x}{\mathrm{Ba}}_x{\mathrm{CuO}}_4(x=1/8)$ by means of muon-spin-rotation experiments. The corresponding OIE exponents were found to be ${\alpha }_{T_{\text{so}}}=-0.57(6)$ and ${\alpha }_{V_{\mathrm{m}}}=-0.71(9)$, which are sign reversed to ${\alpha }_{T_{\mathrm{c}}}=0.46(6)$ measured for the superconducting transition temperature $T_{\mathrm{c}}$. 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.

Figure 1

Temperature dependence of the diamagnetic moment $m_{\text{ZFC}}$ for the ${}^{16}\mathrm{O}$, ${}^{18}\mathrm{O}$, and back-exchanged (${}^{18}\mathrm{O}\to {}^{16}\mathrm{O}$) samples of LBCO-1/8. The arrows denote the superconducting transition temperatures $T_{\text{c1}}$ and $T_{\text{c2}}$ (see text for an explanation). The inset shows the SC transition near $T_{\text{c1}}$.

Figure 2

The normalized TF asymmetry $A$/$A_0$ plotted as a function of temperature for the ${}^{16}\mathrm{O}$, ${}^{18}\mathrm{O}$, and back-exchanged (${}^{18}\mathrm{O}\to {}^{16}\mathrm{O}$) samples of LBCO-1/8. The crosses mark the spin-stripe order temperatures ${}^{16}{T}_{\mathrm{SO}}$ and ${}^{18}{T}_{\mathrm{SO}}$ for the ${}^{16}\mathrm{O}$ and ${}^{18}\mathrm{O}$ sample, respectively. The solid lines represent fits to the data by means of Eq. (1).

Figure 3

ZF $\mu \mathrm{SR}$ signal $P(t)$ for the ${}^{16}\mathrm{O}$ (a) and ${}^{18}\mathrm{O}$ (b) samples of LBCO-1/8 recorded at $T=5\mathrm{K}$ and $T=50\mathrm{K}$. The solid lines represent fits to the data by means of Eq. (2).

Figure 4

(a) Temperature dependence of the average internal magnetic field $B_{\mu }$ at the muon site for ${}^{16}\mathrm{O}$, ${}^{18}\mathrm{O}$, and back-exchanged (${}^{18}\mathrm{O}\to {}^{16}\mathrm{O}$) samples of LBCO-1/8. The solid lines represent fits of the data to the power law described in the text. (b) The temperature dependence of the magnetic volume fraction $V_{\mathrm{m}}$ for ${}^{16}\mathrm{O}$, ${}^{18}\mathrm{O}$, and back-exchanged (${}^{18}\mathrm{O}\to {}^{16}\mathrm{O}$) samples of LBCO-1/8. The solid lines are fits of the data to the same empirical power law as used for $B_{\mu }(T)$ in (a).