Translational-invariant bipolarons and superconductivity
| Autor: | Lakhno, Victor D. |
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| Rok vydání: | 2020 |
| Předmět: | |
| Zdroj: | Condens. Matter 2020, 5(2), 30 |
| Druh dokumentu: | Working Paper |
| DOI: | 10.3390/condmat5020030 |
| Popis: | A translation-invariant (TI) bipolaron theory of superconductivity based, like Bardeen-Cooper-Schrieffer theory, on Fr\"ohlich Hamiltonian is presented. Here the role of Cooper pairs belongs to TI bipolarons which are pairs of spatially delocalized electrons whose correlation length of a coupled state is small. The presence of Fermi surface leads to stabilization of such states in its vicinity and a possibility of their Bose-Einstein condensation (BEC). The theory provides a natural explanation of the existence of a pseudogap phase preceding the superconductivity and enables one to estimate the temperature of a transition $T^*$ from a normal state to a pseudogap one. It is shown that the temperature of BEC of TI bipolarons determines the temperature of a superconducting transition $T_c$ which depends not on the bipolaron effective mass but on the ordinary mass of a band electron. This removes restrictions on the upper limit of $T_c$ for a strong electron-phonon interaction. A natural explanation is provided for the angular dependence of the superconducting gap which is determined by the angular dependence of the phonon spectrum. It is demonstrated that a lot of experiments on thermodynamic and transport characteristics, Josephson tunneling and angle-resolved photoemission spectroscopy (ARPES) of high-temperature superconductors does not contradict the concept of a TI bipolaron mechanism of superconductivity in these materials. Possible ways of enhancing $T_c$ and producing new room-temperature superconductors are discussed on the basis of the theory suggested. Comment: 60 pages, 20 figures |
| Databáze: | arXiv |
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