Experimental Control of the structure and discovery of emergent quasi-2D conductivity in SrCuO₂ ultra thin films

Ping-Chih Chiang^1*, C.-S. Ku², J.-C. Yang³, Y.-H. Chu⁴, J.-Y. Lin¹

¹Institute of Physics, National Chiao Tung University, Hsinchu, Taiwan
²National Synchrotron Radiation Research Center, Hsinchu, Taiwan
³Institute of Physics, National Cheng Kung University, Tainan, Taiwan
⁴Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan

* Presenter:Ping-Chih Chiang, email:pizejohn@yahoo.com.tw

Two-dimensional (2D) CuO₂ plane plays a key role in high-Tc superconductivity. A recent theoretical study predicted a transition from the chain-type structure to the bulk plane-type structure in SrCuO₂ films with thickness larger than five unit-cells (u.c.). In present study, by using pulsed laser-deposition technique SrCuO₂ ultrathin (1 - 20 u.c.) films were successfully grown on TiO₂ terminated SrTiO₃ substrates. The thickness-dependent structural transformation of the SrCuO₂ films were studied by synchrotron base x-ray diffraction, polarized X-ray absorption spectroscopy (XAS) at the Cu L edge as well as x-ray Laue nano diffraction. From synchrotron based x-ray diffraction and XAS measurements shown a bulk planar-type to a chain-type structure transformation upon reducing the thickness below 7 u.c. or 10 u.c. depending on the capping layer. Furthermore, the energy scan of X-ray Laue nano diffraction confirms that the chain-type SCO remained when the planar type SCO develop. The coexist of two phases shade a new light to design/fabricate single layer CuO₂, that can provide a new route to study the fundamental high Tc cuprates physics.

Keywords: SrCuO₂, monolayer copper oxide plane, structural transformation, superconductivity, oxygen sublattice