The Kitaev honeycomb model is exactly solvable — a rare gift in condensed matter theory. Spins on a honeycomb lattice with bond-dependent Ising interactions fractionalize into Majorana fermions and a static gauge field. The ground state is a quantum spin liquid: no magnetic order, long-range entanglement, and exotic anyonic excitations. The material α-RuCl₃ is the closest experimental realization, though it orders magnetically at low temperatures because interactions beyond the pure Kitaev model — Heisenberg exchange, off-diagonal terms — push it away from the spin liquid phase.
Cônsoli, Day-Roberts, Knolle, Botana, and Erten (arXiv 2602.22310, February 2026) propose a way to push it back: stacking α-RuCl₃ on top of an antiferromagnet (MnPS₃) in a van der Waals heterostructure. The antiferromagnetic substrate generates a staggered effective magnetic field in the Kitaev layer — a field that points one direction on sublattice A and the opposite direction on sublattice B. This staggered field, arising from the proximity effect rather than an external magnet, drives the Kitaev material into phases inaccessible to uniform fields.
The phase diagram is rich. Depending on the strength and direction of the staggered field, the system enters an antichiral Kitaev spin liquid (a spin liquid with broken chirality between sublattices), a nonmagnetic nematic phase (rotational symmetry broken without magnetic order), and various skyrmion crystal configurations (periodic arrays of topological spin textures). These phases don't exist in the isolated Kitaev material. They don't exist in the isolated antiferromagnet. They exist only in the interface region, created by the coupling between the two.
The approach exploits a structural advantage of van der Waals materials: layers interact weakly enough to preserve their individual electronic identities but strongly enough to generate measurable proximity effects. The antiferromagnet acts on the Kitaev layer without being significantly perturbed by it. The staggered field is a consequence of the antiferromagnet's broken symmetry — its alternating spin sublattices — imprinting onto the Kitaev layer through interlayer exchange. First-principles calculations confirm that the exchange coupling in the α-RuCl₃/MnPS₃ system is strong enough to access the predicted phases.
The broader principle: a material's phase can be controlled not only by what happens inside it (temperature, pressure, magnetic field, doping) but by what you put next to it. The neighbor defines the neighborhood.