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COMEPHS Sintesi della relazione

Project ID: 517039
Finanziato nell'ambito di: FP6-NMP
Paese: Greece

Final Report Summary - COMEPHS (Controlling mesoscopic phase separation)

The ultimate aim of the COMEPHS project was to comprehend, manipulate and control the inherent phase separation mechanism in manganites, superconductors and the related compounds in order to manipulate the self-organised structure and use the technique in nanotechnology creating functional textured states. By controlling an array of textured phases analogous to those in liquid crystals COMEPHS aimed to control locally the electronic structure and properties without atomic-scale fabrication. The long-term goal of the research was to provide a basis for a new set of electronic technology based on the manipulation of soft electronic matter.

One effort was to identify and produce adequate materials. In this respect, the field of perovskite oxides was exploited and especially the manganites for which there was clear evidence for stable textures electronic states. Besides manganites, the project investigated a series of related compounds for which there was strong evidence that they exhibit electronic phase separation, such as the cuprates, vanadates, cobaltates, organic compounds, diborides or even the newly discovered pnictides, which showed high-transition temperature to superconductivity. These new compounds were prepared in the form of high-quality polycrystalline, single crystals or as thin layers and were characterised by various techniques (diffraction, thermodynamic, optical, transport, magnetic measurements) in order to identify regions of electronic phase separation and defect structures that could be exploitable.

The second step was the identification of the adequate nanostructures. In this respect, a number of compounds and thin films was produced and the effect external perturbations (pressure, magnetic field, X-ray illumination), as well as the substrate (various combinations of films and substrates, orientation of the substrate, lattice mismatch, film thickness, film development conditions) on the physical behaviour of the inhomogeneous electronic states was studied in detail. The studies showed possible ways for the manipulating the textures.

The feasibility of using pressure, X-ray illumination, substrate tailoring or incisions by ion beam microscope on thin films, and finally, magnetic fields was demonstrated. All these methods were studied in detail. The final outcome was a series of examples in which the manipulation of the texture was established as induced by various experimental techniques. Furthermore, the textured states were visualised with the most advanced techniques currently available. Spectacular images of inhomogeneous electronic states were constructed from several partners, which unambiguously map the static phase separation in the real space. Such space modulation in the physical properties provided clear evidence for the feasibility of controlling the phase separation for operational devices. Characteristic examples of one-dimensional and checkerboard modulations of the carrier density were reported. The textured states were fully characterised by almost all experimental groups using a complete set of experimental techniques including transport, Raman, infrared, Nuclear magnetic resonance (NMR) and photoemission. The central objective was the understanding of the influence of external parameters such as pressure or magnetic fields on the physical behavior of the materials or nanostructures at hand. The partners for the first time had the opportunity to study by various techniques the same batch of samples and induce direct information about the underlying mechanisms without any uncertainties by the sample inhomogeneities that can be introduced during the preparation procedure.

Amongst the scientific activities of COMEPHS was to generate the necessary knowledge of the inhomogeneous electronic states and their means of manipulation. Important new results that provide basis for a better focus of the whole activity in the project were generated. Numerous problems were investigated that include the study of superstructures induced by orbital ordering in strongly correlated systems, the role of polaronic effects and Feshbach resonances in a two-component situation. Finally, two workshops were organised in Greece that attracted leading scientists in the field from the entire world helping the dissemination of the acquired knowledge.

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