String Condensation—An Unification of Light and Fermions

Geometrical frustration versus Kitaev interactions in BaCo 2 (AsO 4 ) 2

“…There have been tremendous efforts to realize the Kitaev spin liquid (KSL), which is the ground state of the exactly solvable spin-1/2 model with the bond-dependent Ising interactions on the honeycomb lattice. The KSL is characterized by exotic excitations such as ℤ 2 gauge fluxes and Majorana fermions ( 1 – 10 ), and may serve as a platform for topological quantum computation ( 11 , 12 ). In the majority of candidate Kitaev materials, the physical mechanism to induce the bond-dependent Kitaev interaction relies on exchange processes between spins formed by 4d and 5d ions with large spin–orbit coupling (SOC), such as Ru 3+ and Ir 4+ ( 13 , 14 ).…”