Codimension-two spiral spin liquid in the effective honeycomb-lattice compound Cs3⁢Fe2⁢Cl9

Abstract

A codimension-two spiral spin liquid is a correlated paramagnetic state with one-dimensional ground state degeneracy hosted within a three-dimensional lattice. Here, via neutron scattering experiments and numerical simulations, we establish the existence of a codimension-two spiral spin liquid in the effective honeycomb-lattice compound Cs3⁢Fe2⁢Cl9, which demonstrates an alternate path to spiral spin liquids by overcoming the long-standing impediment of weak further-neighbor interactions. In the long-range ordered regime, competing spiral and spin density wave orders emerge as a function of applied magnetic field, among which a possible order-by-disorder transition is identified.