Generation of isolated flat bands with tunable numbers through Moir\'e engineering

Abstract

Unlike the spin-1/2 fermions, the Lieb and Dice lattices both host triply-degenerate low-energy excitations. Here, we discuss Moir\'e structures involving twisted bilayers of these lattices, which are shown to exhibit a tunable number of isolated flat bands near the Fermi level. These flat bands remain isolated from the high-energy bands even in the presence of small higher-order terms and chiral-symmetry-breaking interlayer tunneling. At small twist angles, thousands of flat bands can be generated to substantially amplify flat band physics. We demonstrate that these flat bands carry substantial quantum weight so that upon adding a BCS-type pairing potential, the associated superfluid weight would also be large, and the critical superconducting temperature would be tunable. Our study suggests a new pathway for flat-band engineering based on twisted bilayer Lieb and Dice lattices.