Controlled Intergrowth of 248 and 247 Phases of Y-Ba-Cu-O in Epitaxial Films and Heterostructures*

Recent studies have shown that superconductivity in the Y-Ba-Cu-O (YBCO) family of cuprates can also be rooted in the quasi-1D Cu-O chains [1], even when the $\rm{CuO_2}$ planes are not conducting [2]. The critical temperature ($T_c$) depends on the phase of YBCO present, such as $\rm{Y_2Ba_4Cu_8O_{16}}$ (248) and $\rm{Y_2Ba_4Cu_7O_{15}}$ (247). Recent studies have also shown that heterostructuring YBCO with other oxides such as $\rm{La_{2/3}Ca_{1/3}MnO_3}$ (LCMO) can strongly influence the former's $T_c$ [3]. This talk reports on a reexamination of these issues, by probing and controlling the intergrowth of the various YBCO phases in thin films and heterostructures. The samples were grown epitaxially by pulsed laser-ablated deposition, and characterized by electrical transport, XRD and high-resolution TEM with in-situ EELS. We observed the presence of 248 and 247 phases in YBCO/LCMO heterostructures. We also observed conversion between different phases of YBCO depending on the thermodynamics of the growth and annealing conditions. The implication of our results on the $T_c$ variation in YBCO/LCMO heterostructure is discussed. \\[4pt] [1] J. Ngai \emph{et al.}, PRL. 98, 177003 (2007).\\[0pt] [2] E. Berg \emph{et al.}, PRB. 76, 214505 (2007).\\[0pt] [3] Z. Sefrioui \emph{et al.}, PRB. 67, 21451 (2003)