Gapless spinons and a field-induced soliton gap in the hyperhoneycomb Cu oxalate framework compound [( C2H5)3NH]2

Frustrated magnets can be platforms for quantum spin-liquid states. A putative spin-liquid candidate, the hyperhoneycomb Cu oxalate framework compound [(C${}_{2}$H${}_{5}$)${}_{3}$NH]${}_{2}$Cu${}_{2}$(C${}_{2}$O${}_{4}$)${}_{3}$ exhibits the absence of long-range order and presence of charge-neutral excitations in the Mott insulating state at low temperatures. Here, the authors demonstrate experimental evidence for gapless spinons and a field-induced soliton gap in this material with the aid of theoretical calculations, and attribute them to weakly coupled antiferromagnetic Heisenberg chains, rather than a previously proposed spin-liquid state.