Practical vortex diodes from pinning enhanced YBa2Cu3O7-delta

We identify a scalable, practical route to fabricating a superconducting diode. The device relies for its function on the barrier to flux vortex entry being reduced at the substrate interface of a superconducting pinning enhanced YBa2Cu3O7-d nano-composite film. We show that these composite systems provide a practical route to fabricating a useful superconducting diode and demonstrate the rectification of an alternating current.This work was supported by the Engineering and Physical Science Research Council [grant numbers EP/C011554/1, EP/C011546/1] and the EU Marie Curie Excellence programme [grant number MEXT-CT-2004- 014156]

Benefits of current percolation in superconducting coated conductors

The critical currents of MOD/RABiTS and PLD/IBAD coated conductors have been measured as a function of magnetic field orientation and compared to films grown on single crystal substrates. By varying the orientation of magnetic field applied in the plane of the film, we are able to determine the extent to which current flow in each type of conductor is percolative. Standard MOD/RABiTS conductors have also been compared to samples whose grain boundaries have been doped by diffusing Ca from an overlayer. We find that undoped MOD/RABiTS tapes have a less anisotropic in-plane field dependence than PLD/IBAD tapes and that the uniformity of critical current as a function of in-plane field angle is greater for MOD/RABiTS samples doped with Ca.EPSRC US Department of Energ

Topological semimetallic phase in PbO2 promoted by temperature

© 2019 American Physical Society. Materials exhibiting topological order host exotic phenomena that could form the basis for novel developments in areas ranging from low-power electronics to quantum computers. The past decade has witnessed multiple experimental realizations and thousands of predictions of topological materials. However, it has been determined that increasing temperature destroys topological order, restricting many topological materials to very low temperatures and thus hampering practical applications. Here, we propose a material realization of temperature-promoted topological order. We show that a semiconducting oxide that has been widely used in lead-acid batteries, β-PbO2, hosts a topological semimetallic phase driven by both thermal expansion and electron-phonon coupling upon increasing temperature. We identify the interplay between the quasi-two-dimensional nature of the charge distribution of the valence band with the three-dimensional nature of the charge distribution of the conduction band as the microscopic mechanism driving this unconventional temperature dependence. Thus, we propose a general principle to search for and design topological materials whose topological order is stabilized by increasing temperature. This provides a clear roadmap for taking topological materials from the laboratory to technological devices

Defects in complex oxide thin films for electronics and energy applications: Challenges and opportunities

This review focuses on recent progress in defect-engineered novel functionalities of complex oxide thin films for electronics and energy applications, and current challenges and perspectives.J.L.M.-D. also acknowledges support from the Royal Academy of Engineering, Grant CiET1819_24, and the ERC POC grant, 779444, Portapower. K.H.L.Z. is grateful for funding support from the National Natural Science Foundation of China (Grant No. 21872116)

Lithium outdiffusion in LiTi<inf>2</inf>O<inf>4</inf> thin films grown by pulsed laser deposition

We report surface chemical cation composition analysis of high quality superconducting LiTi$_{2}$O$_{4}$ thin films, grown epitaxially on MgAl$_{2}$O$_{4}$ (111) substrates by pulsed laser deposition. The superconducting transition temperature of the films was ~13.8 K. Surface chemical composition is crucial for the formation of a good metal/insulator interface for integrating LiTi$_{2}$O$_{4}$ into full-oxide spin-filtering devices in order to minimize the formation of structural defects and increase the spin polarisation efficiency. In consideration of this, we report a detailed angle resolved x-ray photoelectron spectroscopy analysis. Results show Li segregation at the surface of LiTi$_{2}$O$_{4}$ films. We attribute this process due to outdiffusion of Li toward the outermost LiTi$_{2}$O$_{4}$ layers.The research leading to these results has received funding from the European Union Seventh Framework Programme ([FP7/2007–2013] [FP7/2007–2011]) under Grant agreement 316657 (SpinIcur), the European Research Council AdG (291442 “Superspin”), European Research Council AdG (247276 “NOVOX”) and the EPSRC (Equipment Account Grant EP/K035282/1).This is the final version of the article. It first appeared from Elsevier via https://doi.org/10.1016/j.jcrysgro.2016.09.01

Fabrication of ZnO/Cu<inf>2</inf>O heterojunctions in atmospheric conditions: Improved interface quality and solar cell performance

Zn_1-xMg_xO/Cu_2O heterojunctions were successfully fabricated in open-air at low temperatures via atmospheric atomic layer deposition of Zn_1-xMg_xO on thermally oxidized cuprous oxide. Solar cells employing these heterojunctions demonstrated a power conversion efficiency exceeding 2.2% and an open-circuit voltage of 0.65 V. Surface oxidation of Cu_2O to CuO prior to and during Zn_1-xMg_xO deposition was identified as the limiting factor to obtaining a high quality heterojunction interface. Optimization of deposition conditions to minimize Cu_2O surface oxidation led to improved device performance, tripling the open-circuit voltage and doubling the short-circuit current density. These values are the highest reported for a ZnO/Cu_2O interface formed in air, and highlight atmospheric ALD as a promising technique for inexpensive and scalable fabrication of ZnO/Cu_2O heterojunctions.This is the final published version. It is also available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0927024814005005#

Strain-tuned enhancement of ferromagnetic TC_{C} to 176 K in Sm-doped BiMnO3_{3} thin films and determination of magnetic phase diagram

BiMnO$_{3}$ is a promising multiferroic material but it’s ferromagnetic T$_{C}$ is well below room temperature and the magnetic phase diagram is unknown. In this work, the relationship between magnetic transition temperature (T$_{C}$) and the substrate induced (pseudo-) tetragonal distortion (ratio of out-of-plane to in-plane lattice parameters, c/a) in BiMnO$_{3}$ thin films, lightly doped to optimize lattice dimensions, was determined. For c/a > 0.99, hidden antiferromagnetism was revealed and the magnetisation versus temperature curves showed a tail behaviour, whereas for c/a < 0.99 clear ferromagnetism was observed. A peak T$_{C}$ of up to 176 K, more than 70 K higher than for bulk BiMnO$_{3}$, was achieved through precise strain tuning. The T$_{C}$ was maximised for strong tensile in-plane strain which produced weak octahedral rotations in the out-of-plane direction, an orthorhombic-like structure, and strong ferromagnetic coupling.This work was supported by the European Research Council (ERC) (Advanced Investigator grant ERC-2009-AdG-247276-NOVOX), the Engineering and Physical Sciences Research Council (EPSRC) (Equipment Account Grant EP/K035282/1) and the Isaac Newton Trust (Minute 13.38(k))

Determining interface structures in vertically aligned nanocomposite films

Vertically aligned nanocomposite (VAN) films have self-assembled pillar-matrix nanostructures. Owing to their large area-to-volume ratios, interfaces in VAN films are expected to play key roles in inducing functional properties, but our understanding is hindered by limited knowledge about their structures. Motivated by the lack of definitive explanation for the experimentally found enhanced ionic conductivity in Sm-doped-CeO2/SrTiO3 VAN films, we determine the structure at vertical interfaces using random structure searching and explore how it can affect ionic conduction. Interatomic potentials are used to perform the initial searching, followed by first-principles calculations for refinement. Previously unknown structures are found, with lower energy than that of an optimized hand-built model. We find a strongly distorted oxygen sublattice which gives a complex landscape of vacancy energies. The cation lattice remains similar to the bulk phase, but has a localized strain field. The excess energy of the interface is similar to that of high angle grain boundaries in SrTiO3.China Scholarship Council Cambridge Commonwealth, European and International Trus