Emergence of spinons in layered trimer iridate Ba4Ir3O10

Spinons are well-known as the elementary excitations of one-dimensional antiferromagnetic chains, but means to realize spinons in higher dimensions is the subject of intense research. Here, we use resonant x-ray scattering to study the layered trimer iridate Ba₄Ir₃O₁₀, which shows no magnetic order down to 0.2 K. An emergent one-dimensional spinon continuum is observed that can be well-described by XXZ spin-1/2 chains with magnetic exchange of ∼55 meV and a small Ising-like anisotropy. With 2% isovalent Sr doping, magnetic order appears below TN=130 K along with sharper excitations in (Ba_1−xSr_x)₄Ir₃O₁₀. Combining our data with exact diagonalization calcula- tions, we find that the frustrated intra-trimer interactions effectively reduce the system into decou- pled spin chains, the subtle balance of which can be easily tipped by perturbations such as chemical doping. Our results put Ba₄Ir3O₁₀ between the one-dimensional chain and two-dimensional quan- tum spin liquid scenarios, illustrating a new way to suppress magnetic order and realize fractional spinons.