3d SUSY enhancement with non-trivial Coulomb branch via 4d $\mathcal{N}=2$ SCFT

In recent years, a variety of three-dimensional (3d) $\mathcal{N}=2$ Chern--Simons (CS) matter theories have been constructed that flow to 3d $\mathcal{N}=4$ superconformal field theories (SCFTs) obtained from $R$-twisted reductions of four-dimensional (4d) $\mathcal{N}=2$ SCFTs. In all previously studied examples, the resulting 3d $\mathcal{N}=4$ SCFTs have trivial Coulomb branches. In this paper, we construct a 3d $\mathcal{N}=2$ CS matter theory that flows to the $R$-twisted reduction of the $(A_2,D_4)$ Argyres--Douglas theory. This gives the first example in this class whose infrared 3d $\mathcal{N}=4$ SCFT has a non-trivial Coulomb branch, which we argue is given by the orbifold $\mathbb{C}^2/\mathbb{Z}_2$, while its Higgs branch is trivial. We further identify the 4d $U(1)$ R-charge as a mixing of a 3d R-charge with an emergent 3d Coulomb branch flavor charge that has no 4d origin.