Surface Functional Renormalization Group for Layered Quantum Materials

ABSTRACT We present an extension to the 2D functional renormalization group to efficiently treat interactions on the surface or at interfaces of 3D systems. As an application, we consider a semi‐infinite stack of 2D square lattices, including a Hubbard interaction on the surface layer and an alternating interlayer coupling. We investigate how strongly correlated states of the decoupled 2D Hubbard model on the surface evolve under inclusion of such an SSH‐like interlayer coupling. For large parts of the phase diagram as a function of the interlayer hopping parameters, the physics of the 2D system prevails, with antiferromagnetic, superconducting ‐wave, and ferromagnetic correlations taking center stage. However, for intermediate interlayer couplings the superconducting state at intermediate interaction strengths separates into two regimes by a small region of incommensurate spin‐density‐wave and spin‐bond order, enabling the potential realization of chiral spin‐bond order.