Investigation into the “1/8 anomaly” in superconducting cuprates: La2-xBaxCuO4 (x=0.125)

The superconducting material La2-xBaxCuO4 (LBCO) exhibits an anomalous dip in Tc at the x = 0.125 composition at low temperature (>30 K). This is at odds with other superconducting materials such as La2−xSrxCuO4 that have a superconducting dome in the region x = 0-0.2, with a maximum Tc at x=0.125. The suppression of superconductivity in LBCO is coincident with an anomaly in the sequence of structural phase transition from orthorhombic to tetragonal, on cooling below 60 K. To disentangle the effects of changing ionic radii (with x), and single ion anisotropy, we have synthesised and observed analogous phase transitions, but at higher temperatures, in a sample with 50% of the Jahn-Teller active Cu2+ replaced by inactive Mg2+. By performing high pressure neutron diffraction we will gain further insight into this unusual sequence of phase transitions that acts to suppress superconductivity.