Probing multi-spinon excitations outside of the two-spinon continuum in the antiferromagnetic spin chain cuprate Sr 2 CuO 3

• Published in: Nature communications 2018-12, Vol.9 (1), p.5394
• Main Authors: Schlappa, J, Kumar, U, Zhou, K J, Singh, S, Mourigal, M, Strocov, V N, Revcolevschi, A, Patthey, L, Rønnow, H M, Johnston, S, Schmitt, T
• Format: Article
• Language: English
• ISSN: 2041-1723
• DOI: 10.1038/s41467-018-07838-y

One-dimensional (1D) magnetic insulators have attracted significant interest as a platform for studying quasiparticle fractionalization, quantum criticality, and emergent phenomena. The spin-1/2 Heisenberg chain with antiferromagnetic nearest neighbour interactions is an important reference system; its elementary magnetic excitations are spin-1/2 quasiparticles called spinons that are created in even numbers. However, while the excitation continuum associated with two-spinon states is routinely observed, the study of four-spinon and higher multi-spinon states is an open area of research. Here we show that four-spinon excitations can be accessed directly in Sr CuO using resonant inelastic x-ray scattering (RIXS) in a region of phase space clearly separated from the two-spinon continuum. Our finding is made possible by the fundamental differences in the correlation function probed by RIXS in comparison to other probes. This advance holds promise as a tool in the search for novel quantum states and quantum spin liquids.