Asymptotic flat band superconductivity in twisted bilayer graphene and other systems
Abstract: The effective attractive interaction between electrons, mediated by electron-phonon coupling, is a well-established mechanism of conventional superconductivity. In metals exhibiting a Fermi surface, the critical temperature of superconductivity is exponentially smaller than the characteristic phonon energy. Therefore such superconductors are found only at temperatures below a few Kelvin. In contrast, electron systems with exotic energy dispersion exhibit different functional dependence on electron-phonon coupling, and can in principle host a superconducting state at much higher temperatures. We have in particular studied electron-phonon mediated superconductivity in systems with asymptotically flat bands . There, the critical temperature is a linear function of the effective attractive interaction [2,3]. A particularly interesting case is that of twisted bilayer graphene. It holds an approximate flat band at certain magic twisting angles, and recent experiments ! have demonstrated the presence of superconductivity in such systems. In my talk I will discuss these findings from the perspective of flat-band superconductivity mediated by electron-phonon interaction . In addition, I will discuss other model systems possibly exhibiting flat-band superconductivity.
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