Substrate surface engineering for tailoring properties of functional ceramic thin films

Using oxide substrates for functional ceramic thin film deposition beyond their usual application as chemical inert, lattice-matched support for the films represents a novel concept in ceramic thin film research. The substrates are applied as a functional element in order to controllably modify the atom arrangement and the growth mode of ceramic prototype materials such as cuprate superconductors and colossal magnetoresistance manganites. One example is the use of epitaxial strain to adjust the relative positions of cations and anions in the film and thus modify their physical properties. The other makes use of vicinal cut SrTiO3 which enables the fabrication of regular nanoscale step and terrace structures. In YBa2Cu3O7-x thin films grown on vicinal cut SrTiO3 single crystals a regular array of antiphase boundaries is generated causing an anisotropic enhancement of flux-line pinning. In the case of La-Ca-Mn-O thin films grown on vicinal cut substrates it could be demonstrated that magnetic in-plane anisotropy is achieved.Comment: 6 page

On Magnetic Interlayer Coupling and Proximity Effect in a La0.67_{0.67}Ca0.33_{0.33}MnO3_3(10 nm)/YBa2_2Cu3_3O7_7(10 nm) Superlattice

We present a study of interlayer coupling and proximity effects in a La$_{0.66}$Ca$_{0.33}$MnO$_3$(10 nm)/YBa$_2$Cu$_3$O$_7$(10 nm) superlattice. Using element-sensitive x-ray probes, the magnetic state of Mn can be probed without seeing the strong diamagnetism of the superconductor, which makes this approach ideal to study changes in the magnetic properties across the superconducting transition. By a combined experiment using {\it in situ} transport measurements during polarized soft x-ray measurements, we were able to see no noticeable influence of the superconducting state on the magnetic properties and no evidence for magnetic coupling across a 10 nm YBCO layer.Comment: 4 pages, submitted to Applied Physics Letter

Science and technology of cuprate-based high temperature superconductor thin films, heterostructures and superlattices — the first 30 years (Review Article)

During the three decades after the discovery of superconductivity at high temperatures in copper oxides, intense research activities generated a tremendous progress in both, mastering the scientific challenges underpinning the understanding of the properties of these chemically and structurally complex materials as well as achieving a mature technology in preparing single phase bulk specimens—including single crystals—and epitaxially grown single crystalline thin films. This review covers in addition to more basic physics oriented developments mainly technological aspects of complex oxide thin film deposition as an enabling technology to explore the physics of these materials. It consists of two parts: after a brief introduction to the materials development prior to the discovery of superconducting copper oxides, a description of the relevant properties of copper oxide superconductors with focus on YBa₂Cu₃O₇−δ is given, followed by the coverage of essentials of complex oxide thin film deposition technology with the copper oxides at its core. Here, the major physical vapor deposition technologies (evaporation and oxide molecular beam technology, sputtering and pulsed laser deposition) are described followed by an overview of substrate requirements to deposit high quality thin films. Opportunities by choosing special substrates with unique properties far beyond the usual mechanical support for a film are introduced with examples aside from usual lattice mismatch induced strain effects. One is the continuous modification of the strain state by poling ferroelectric oxide substrates linked to a piezoelectric effect, the other is the nanoscale tailoring of substrate step-and-terrace structures resulting in a controllable generation of planar defects in complex oxides, thus contributing to the physics of flux-line pinning in cuprate superconductors. In the second part of this review, first some highlights of single layer thin film research are given such as to tailor thin film orientation, generating well defined antiphase boundaries in YBa₂Cu₃O₇−δ thin films as flux-line pinning centers as well as contributions to understand fluctuation conductivity in relation to the pseudogap state. In the last section new developments in high Tc cuprate based heterostructures and superlattices are reviewed with a special focus on the opportunities offered by interface-induced electronic interactions

A study of the ferromagnetic transition of SrRuO3SrRuO_3 in nanometer thick bilayers with YBa2Cu3OyYBa_2Cu_3O_y, La1.88Sr0.12CuO4−yLa_{1.88}Sr_{0.12}CuO_{4-y}, Au and Cr: Signature of injected carriers in the pseudogap regime

The hypothesis regarding the existence of uncorrelated pre-formed pairs in the pseudogap regime of superconducting $YBa_2Cu_3O_y$ is tested experimentally using bilayers of $YBa_2Cu_3O_y$ and the itinerant ferromagnet $SrRuO_3$. In our study, we monitor the influence of $YBa_2Cu_3O_y$ on $T_p$, the ferromagnetic ordering temperature of $SrRuO_3$. Here, $T_p$ is the temperature of maximum dM/dT or dR/dT where M and R are the magnetization and resistance of $SrRuO_3$, respectively. We compare the results with similar measurements carried out on bilayers of $La_{1.88}Sr_{0.12}CuO_{4-y}$, $Au$ and $Cr$ with $SrRuO_3$. We find that in bilayers made of underdoped 10 nm $YBa_2Cu_3O_y$/5 nm $SrRuO_3$, the $T_p$ values are shifted to lower temperatures by up to 6-8 K as compared to $T_p\approx 140$ K of the 5 nm thick reference $SrRuO_3$ film. In contrast, in the other type of bilayers, which are not in the pseudogap regime near $T_p$, only a smaller shift of up to $\pm$2 K is observed. These differences are discussed in terms of a proximity effect, where carriers from the $YBa_2Cu_3O_y$ layer are injected into the $SrRuO_3$ layer and vice versa. We suggest that correlated electrons in the pseudogap regime of $YBa_2Cu_3O_y$ are responsible for the observed large $T_p$ shifts.Comment: 9 figure

Enhancement of flux-line pinning in all-oxide superconductor/ferromagnet heterostructures

We have studied the local critical current density, jc, in the superconductor thin film of bilayer structures consisting of YBa2Cu3O7 and the ferromagnets La2/3Ca1/3MnO3 and SrRuO3, respectively, by means of quantitative magneto-optics. A pronounced hysteresis of jc was observed which is ascribed to the magnetization state of the ferromagnetic layer. The results are discussed within the frame of magnetic vortex - wall interactions.Comment: 9 page