Anisotropic effect of field on the orthorhombic-to-tetragonal transition in the striped cuprate (La,Nd)2 − xSrxCuO4

The Nd-doped cuprate La2 − y − xNdySrxCuO4 displays a first-order phase transition at Td (= 74 K for x=0.10, y = 0.60) to a low-temperature tetragonal (LTT) phase. A magnetic field H applied ∥ the a-axis leads to an increase in Td, whereas Td is decreased when H∥c. The field couples to the LTO-LTT instability in an anisotropic way that is not understood. Related anisotropic effects are observed in the uniform susceptibility and the in-plane magnetoresistance.