Title: Atomic-scale identification of novel planar defect phases in heteroepitaxial YBa$_2$Cu$_3$O$_{7-δ}$ thin films,
Abstract: We have discovered two novel types of planar defects that appear in
heteroepitaxial YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO123) thin films, grown by
pulsed-laser deposition (PLD) either with or without a
La$_{2/3}$Ca$_{1/3}$MnO$_3$ (LCMO) overlayer, using the combination of
high-angle annular dark-field scanning transmission electron microscopy
(HAADF-STEM) imaging and electron energy loss spectroscopy (EELS) mapping for
unambiguous identification. These planar lattice defects are based on the
intergrowth of either a BaO plane between two CuO chains or multiple Y-O layers
between two CuO$_2$ planes, resulting in non-stoichiometric layer sequences
that could directly impact the high-$T_c$ superconductivity.