CC BY 4.0 UnportedClancy, J.P.Gretarsson, H.Sears, J.A.Singh, Y.Desgreniers, S.Mehlawat, K.Layek, S.Rozenberg, G.K.Ding, Y.Upton, M.H.Casa, D.Chen, N.Im, J.Lee, Y.Yadav, R.Hozoi, L.Efremov, D.Van Den Brink, J.Kim, Y.-J.2020-07-202020-07-202018https://doi.org/10.34657/3672https://oa.tib.eu/renate/handle/123456789/5043Honeycomb-lattice quantum magnets with strong spin-orbit coupling are promising candidates for realizing a Kitaev quantum spin liquid. Although iridate materials such as Li2IrO3 and Na2IrO3 have been extensively investigated in this context, there is still considerable debate as to whether a localized relativistic wavefunction (J eff = 1/2) provides a suitable description for the electronic ground state of these materials. To address this question, we have studied the evolution of the structural and electronic properties of α-Li2IrO3 as a function of applied hydrostatic pressure using a combination of X-ray diffraction and X-ray spectroscopy techniques. We observe striking changes even under the application of only small hydrostatic pressure (P ≤ 0.1 GPa): A distortion of the Ir honeycomb lattice (via X-ray diffraction), a dramatic decrease in the strength of spin-orbit coupling effects (via X-ray absorption spectroscopy), and a significant increase in non-cubic crystal electric field splitting (via resonant inelastic X-ray scattering). Our data indicate that α-Li2IrO3 is best described by a J eff = 1/2 state at ambient pressure, but demonstrate that this state is extremely fragile and collapses under the influence of applied pressure.enghttps://creativecommons.org/licenses/by/4.0/530Kitaev quantum spin liquidHoneycomb-lattice quantum magnetsspin-orbit couplingArticle