Phase diagram of a distorted kagome antiferromagnet and application to Y-kapellasite

We investigate the magnetism of a previously unexplored distorted spin-1/2 kagome model consisting of three symmetry-inequivalent nearest-neighbor antiferromagnetic Heisenberg couplings J_⬡, J, and J^′, and uncover a rich ground state phase diagram even at the classical level. Using analytical arguments and numerical techniques we identify a collinear Q→ = 0 magnetic phase, two unusual non-collinear coplanar Q→ = (1 / 3 , 1 / 3) phases and a classical spin liquid phase with a degenerate manifold of non-coplanar ground states, resembling the jammed spin liquid phase found in the context of a bond-disordered kagome antiferromagnet. We further show with density functional theory calculations that the recently synthesized Y-kapellasite Y₃Cu₉(OH)₁₉Cl₈ is a realization of this model and predict its ground state to lie in the region of Q→ = (1 / 3 , 1 / 3) order, which remains stable even after the inclusion of quantum fluctuation effects within variational Monte Carlo and pseudofermion functional renormalization group. The presented model opens a new direction in the study of kagome antiferromagnets.