Electron-lattice coupling and stripe formation inLa2−xBaxCuO4

Abstract

The temperature dependence of the resistance $R(T)$ and the thermoelectric power $\ensuremath{\alpha}(T)$ under different hydrostatic pressures $P$ are reported for polycrystalline ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ba}}_{x}{\mathrm{CuO}}_{4},$ $0.11<~x<~14;$ they reveal a minimum in $R(T)$ and an abrupt change in the sign of $\ensuremath{\alpha}(T)$ at a transition from the low-temperature tetragonal (LTT) to the low-temperature orthorhombic phase. Superconductivity is suppressed at ambient pressure in the range $0.12<~x<~0.13,$ where neutron-diffraction data have shown a static charge ordering into hole-rich and magnetic stripes, but pressure introduces $n$-type superconductivity into these compositions within the LTT phase with a ${\mathrm{dT}}_{0}/dP\ensuremath{\approx}1.0\mathrm{K}/\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}.$ The $x=0.14$ sample is superconductive at ambient pressure in the LTT phase, and ${\mathrm{dT}}_{0}/dP>0$ changes to ${\mathrm{dT}}_{0}/dP=0$ at a ${P}_{c}\ensuremath{\approx}10\mathrm{kbar}.$ No anomaly in the transport properties is found at the magnetic ordering temperature ${T}_{N}\ensuremath{\approx}30\mathrm{K}$ in the LTT phase. These data, which show no support for stripe formation and superconductivity resulting from magnetic interactions, are found to be compatible with a model of strong coupling of charge carriers in coherent electronic states to fluctuations in the Cu-O bond lengths. Periodically alternating stripes of hole-rich and magnetic domains in the ${\mathrm{CuO}}_{2}$ sheets are pinned, for $x\ensuremath{\approx}1/8,$ by the crystallographic distortion of the LTT phase; but the application of hydrostatic pressure, which decreases the magnitude of the LTT deformation, restores superconductivity apparently by depinning the stripes.