Agenda

Résumé : It is well known and intuitively understandable that magnetic couplings in materials decrease extremely rapidly as the distance between localized spins increases. In this study, we reveal an unusual and unexpected phenomenon that completely challenges and contradicts this well-established fact. It is possible in flat-band (FB) materials to significantly amplify (orders of magnitude) the magnetic couplings between widely separated spins. We show that the underlying mechanism that enables the boost of the magnetic couplings is connected to a geometric characteristic of FB eigenstates known as the quantum metric (QM). The QM provides a measure of the square of the typical spread of FB eigenstates. It plays an essential role in explaining the origin of the superconducting phase in twisted bilayer graphene in the vicinity of magic angles. We believe that our findings could be of great interest in the search for high temperature 2D ferromagnetic systems and for long-distance quantum communication that requires lossless transfer of a quantum state between distant quantum registers.