Anisotropic Band Flattening in Twisted Bilayer of M-Valley MXenes

Abstract: Experimental studies on moir\'e materials have predominantly focused on twisted hexagonal lattice with low-energy states near the $\Gamma$- or K-points. These materials, characterized by isotropic low-energy dispersion, are fundamentally distinct from those with anisotropic properties. Here we introduce a series of semiconducting transition metal carbides (MXenes) $M_2$C$T_2$ ($M$ = Ti, Zr, Hf, Sc, Y; $T$ = O, F, Cl) as a novel platform for M-valley moir\'e materials. Take Ti$_2$CO$_2$ and Zr$_2$CO$_2$ as representative examples, large-scale \emph{ab initio} calculations show that their AB-stacked twisted homobilayer features three three-fold rotational symmetry related M-valleys with time-reserval symmetry and giant anisotropic band flattening. We derive a simplified moir\'e Hamiltonian for these systems and conduct a detailed analysis of their band structures, where the origins of anisotropic band flattening are clearly elucidated. This research broadens the scope of moir\'e materials, where the valley- and spin-degenerate two-dimensional array of quasi-one-dimensional system could serve as a potential platform for realizing many interesting correlated phases.