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CCICO Report Summary

Project ID: 291151
Funded under: FP7-IDEAS-ERC
Country: Switzerland

Final Report Summary - CCICO (Coupled and Competing Instabilities in Complex Oxides)

Systems that are close to instabilities are characterized by giant responses to small external perturbations. For example, very large electric polarizations are induced by small applied electric fields in systems such as (Ba,Sr)TiO3 that are close to ferroelectric phase transitions. The resulting responses are often of technological importance -- in this case the high dielectric constants are exploited in capacitor applications -- and the fundamental physics of solids in proximity to such phase transitions is rich, fascinating, and often poorly characterized.

The CCICO project explores the coupling and competition between previously unexplored and / or poorly understood combinations of instabilities and external perturbations both to to develop a comprehensive understanding of how proximity to novel combinations of instabilities, as well as previously unidentified types of ordering, manifest in new behaviors, and to develop design guidelines for practical realization of new materials with these behaviors.

During the course of the CCICO project we made the following key discoveries and developments:

We showed that defect formation energy couples strongly to epitaxial strain in complex oxide thin films, and proposed the chemical potential as an additional conjugate field (with electric, magnetic and stress) for controlling and tuning functionality.

We introduced the concept of magnetoelectric monopolization, explored its relevance for the magnetoelectric effect, and developed and implemented the formalism for its calculation within density functional theory.

We identified a possible order parameter for the hidden order in the pseudo gap phase of the high-Tc cuprate superconductors, which is compatible with all experimental measurements.

We proposed a new mechanism for exotic superconductivity -- pairing mediated by critical ferroelectric fluctutations -- and demonstrated its relevance for the superconducting state of SrTiO3.

We showed that multiferroic YMnO3 provides the first example of Kibble-Zurek scaling in a solid-state system, and used it to extract the mechansim underlying the scaling and to identify a "beyond-Kibble-Zurek" regime.

We established the existence of nanoscale conducting channels at the ferroelectric domain walls in YMnO3 and explored the mechanism for their conductivitiy and their relevance in technological applications.

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