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Routes to Bose-Einstein Condensation at Room Temperature

Final Report Summary - ROBOCON (Routes to Bose-Einstein Condensation at Room Temperature)

In project ROBOCON we considered the possibility of realization of Bose-Einstein Condensation (BEC) in three experimental systems:
- Carbon-based compounds: Graphite, Graphene and Nanotubes
- Exciton-Polariton excitations in semiconductors
- Perovskite Oxides close to Metal-Insulator transition.
that demonstrate the very common feature: the Bose statistic of current (mass) carriers and have the tendency to form the condensed superconducting or/and superfluid state at high temperatures. It is this feature unified the Consortium Members

1) ROMA: University "Tor Vergata", Italy
2) UPJV: Universite de Picardie Jules Verne France
3) UNEXE: University of Exeter, UK
4) UCAM: Universite Cadi Ayyad de Marrakech, Morocco
5) UNICAMP: Universidade Estadual de Campinas, Brazil

with the final objective to understand the realization of BEC phenomena on the experimental and theoretical level in the proposed systems and elaborate the practical recommendations for their further applications in industry.

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Three Work Packages (WPs) were selected according to the mentioned above experimental systems. Each WP included the experimental and theoretical tasks as well as complimentary training of ESRs and ERs in Partner institutions, including the dissemination of acquired knowledge. The main results achieved in course of the Project are as follows.

WP1 Local superconductivity and BEC in Graphite

WP1 had an objective to explore the superconducting properties of doped and structurally disordered patches on Graphite surface and isolated graphene by means of local probe measurements. We worked to understand the formation of excitonic gap in graphite and test it appearance at high (room) temperatures. Nobel Prise 2010 was given for graphene that confirms the importance of studies of electronic properties of carbon-based systems proposed in the Project. This amplified our interests of the carbon-based compounds with concentration on the novel system: graphene. Study of transport phenomena in graphite in ultra-high magnetic field at 10-50T were performed and the fractional quantum Hall effect was discovered in Graphite. We observed a sign change in Hall resistivity from electron- to hole-like that can be associated with the field-driven BEC charge density wave. To understand the properties of Dirac Fermions in finite geometries and the role of confinement in formation of BEC at room temperature we studied the role of excitonic gap local bose-pairs formation and constructed the theory of Dirac charge carriers confinement in finite geometry.

WP2 Exciton - Polariton Bose-Einstein Condensation

The objective of WP2 was to predict and test the realization of room temperature optically induced superconductivity and spin superfluidity, basing on the BEC of exciton-polariton pairs. The theoretical aspects of this objective were completely achieved. Theory the formation of quadron-polaritons obeying bosonic statistics was proposed. Study of the spatial-temporal dynamics of superfluids of exciton- and quadron-polaritons in microcavitity and of formation of Rotons in a Hybrid Bose-Fermi System was also completed. The practical aspects of realization of the proposed ideas and of concrete devices were formulated in general and several signatures of BEC effects were discovered in quantum microcavities. This, in particularly, opens the way to observation of superfluid polariton spins currents.

WP3 Bose-Einstein Condensation in Oxides

The objective of WP3 was to study the possibility of BEC in Sr- and W-based oxides in vicinity of Metal-Insulator crossover, either by variation of chemical composition or by reducing the dimensionality of the system, preparing samples in form of thin films or superlattices. We studied in detail the phenomena in compounds of WO3 structure: PbKLiNbO, GdKNbO and their derivatives (and also similar oxides ZnO, and multiferroic BiFeO3), that are the promising and not yet explored oxides, that can demonstrate the formation of BEC pairs. During work on these oxides we discovered the very reach structural phase diagram that can stimulate formation of BEC pairs of different symmetry. The theory of these transitions was completed. During the experimental investigation of the transport properties we recognized the importance of not yet studied coupling of electrons – with free conducting (the novel research area that is now called as Nanoionics) and devoted a lot of efforts to clarification of their role. Theoretical understanding of bipaloronic and polaronic BEC pairs formation in smart (ferro) electrical oxides was delivered.

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The results of the Project were published as 55 articles in the highest impact international journals and disseminated in 68 scientific conferences, mostly as invited and plenary talks. Substantial part of publications and conference talks was done under bi- and multilateral co-participation of Consortium members.

7 Conferences and workshops, and 2 ESRs training schools were organized in frame of the project. The outside researchers were also involved in this training activity due to attraction of the external matching funds, notably from UNESCO and International Institute of Physics (Brazil).

6 dissertations, including 2 PhD thesis and 1 Habilitation thesis, jointly co-supervised by ROBOCON Partners were delivered up to the end of the Project.

The widespread research network “Mediterranean Electronic Materials MeM” (www.mem.ferroix.net) that unifies the ERA and North Africa researchers countries was created to achieve the objective of the Project, ensure the continuation of the work and achieve the knowledge and technology transfer between REA and Mediterranean neighbor countries.