Self-doped flat band and spin-triplet superconductivity in monolayer 1T-TaSe$_{2-x}$Te$_{x}$

Abstract: Two-dimensional van der Waals materials have become an established platform to engineer flat bands which can lead to strongly-correlated emergent phenomena. In particular, the family of Ta dichalcogenides in the 1\textit{T} phase presents a star-of-David charge density wave that creates a flat band at the Fermi level. For TaS$2$ and TaSe$_2$ this flat band is at half filling leading to a magnetic insulating phase. In this work, we theoretically demonstrate that ligand substitution in the TaSe${2-x}$Te$x$ system produces a transition from the magnetic insulator to a non-magnetic metal in which the flat band gets doped away from half-filling. For $x\in[{0.846},{1.231}]$ the spin-polarized flat band is self-doped and the system becomes a magnetic metal. In this regime, we show that attractive interactions promote three different spin-triplet superconducting phases as a function of $x$, corresponding to a nodal f-wave and two topologically-different chiral p-wave superconducting phases. Our results establish monolayer TaSe${2-x}$Te$_{x}$ as a promising platform for correlated flat band physics leading to unconventional superconducting states.