Effect of superconductivity on the shape of flat bands

V. R. Shaginyan; A. Z. Msezane; M. Ya. Amusia; G. S. Japaridze

doi:10.1209/0295-5075/ac64ba

paper

Effect of superconductivity on the shape of flat bands

arXiv:2103.11848 · doi:10.1209/0295-5075/ac64ba

Abstract

For the first time, basing both on experimental facts and our theoretical consideration, we show that Fermi systems with flat bands should be tuned with the superconducting state. Experimental measurements on magic-angle twisted bilayer graphene of the Fermi velocity $V_{F}$ as a function of the temperature $T_{c}$ of superconduction phase transition have revealed $V_{F} \propto T_{c} \propto 1/ N_{s} (0)$ , where $N_{s} (0)$ is the density of states at the Fermi level. We show that the high- $T_{c}$ compounds $B i_{2} S r_{2} CaC u_{2} O_{8 + x}$ exhibit the same behavior. Such observation is a challenge to theories of high- $T_{c}$ superconductivity, since $V_{F}$ is negatively correlated with $T_{c}$ , for $T_{c} \propto 1/ V_{F} \propto N_{s} (0)$ . We show that the theoretical idea of forming flat bands in strongly correlated Fermi systems can explain this behavior and other experimental data collected on both $B i_{2} S r_{2} CaC u_{2} O_{8 + x}$ and twisted bilayer graphene. Our findings place stringent constraints on theories describing the nature of high- $T_{c}$ superconductivity and the deformation of flat band by the superconducting phase transition.

arXiv comment5 pages, 2 figures

Effect of superconductivity on the shape of flat bands

Abstract

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