Abstract
The superconducting system La2−xBaxCuO4 is known to show a minimum in the transition
temperature, Tc, at x = 1/8 where maximal stripe order is pinned by the anisotropy within the
CuO2 planes that occurs in the low-temperature-tetragonal (LTT) crystal structure. For x = 0.095,
where Tc reaches its maximum value of 32 K, there is a roughly coincident structural transition
to a phase that is very close to LTT. Here we present a neutron scattering study of the structural
transition, and demonstrate how features of it correlate with anomalies in the magnetic susceptibility, electrical resistivity, thermal conductivity, and thermoelectric power. We also present measurements on a crystal with 1% Zn substituted for Cu, which reduces Tc to 17 K, enhances the spin stripe order, but has much less effect on the structural transition. We make the case that the structural transition correlates with a reduction of the Josephson coupling between the CuO2 layers, which interrupts the growth of the superconducting order. We also discuss evidence for two-dimensional superconducting fluctuations in the normal state, analyze the effective magnetic moment per Zn impurity, and consider the significance of the anomalous thermopower often reported in the stripeordered phase.
