University of Twente Student Theses


Electronic polarons in cuprates and pnictides

Rorije, Rob (2015) Electronic polarons in cuprates and pnictides.

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Abstract:A candidate model for explaining pairing in high-Tc superconductors is studied. When electrons polarize nearby ions, this electronic polarization can follow, and alter its properties. An electron together with its polarization is an electronic polaron. This is described analogously to polarons that instead use phonons. Both a static and a dynamic model are described. Two similar existing models, one for FeAs and one for La2CuO4, are discussed and expanded. Both longrange electron-polarization interactions, as well as Coulomb repulsion are added. New parameters in the case of La2CuO4 show no bound state, which is needed for superconductivity. The addition of long-range interaction in the case of FeAs can compensate an unscreened Coulomb repulsion. The model is also applied to a new structure, a monolayer of FeSe grown on a SrTiO3 substrate. This structure has achieved critical temperatures of up to 100 K in experiments. For this structure the model shows that long-range interactions are not enough to compensate the Coulomb repulsion, if we do not take into account the SrTiO3 substrate. SrTiO3 has a high dielectric constant and if we introduce this into the model, we do get a bound state for FeSe. Suggestions are made for further research.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:33 physics
Programme:Applied Physics MSc (60436)
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