The nuclear density of YBCO by the maximum entropy method using neutron powder data

In order to examine the nature of thermal motions of the YBCO superconductor, particularly in the CuO2 and CuO planes, the nuclear density distribution was observed by the maximum entropy method (MEM) using neutron powder diffraction data measured at 15 K. The characteristic squarish deformation of the nuclear density due to anharmonic thermal motion was found even at such a low temperature for the Cu atom in the CuO2 plane but not in the CuO plane. The obtained MEM nuclear density is consistent with the existence of strong Cu-O bonds in the CuO2 plane and not in the CuO plane.