Collapse of susceptibility and non-trivial spin dynamics in the hyper-honeycomb magnet β-Li₂IrO₃ under high pressure

We present high-pressure (2 GPa) ⁷Li nuclear magnetic resonance (NMR) measurements on single crystals of the hyper-honeycomb Kitaev magnet β-Li₂IrO₃. The spectra show evidence for a structural phase transition around 200 K and a coexistence of phases, consistent with the results of other measurement techniques. The NMR spectra and line shift measurements demonstrate a strong suppression of the local magnetic susceptibility at high pressure. However, the spin-lattice relaxation (1/T₁) shows a clear power-law temperature dependence. This is inconsistent with a gapped singlet ground state of dimers and tetramers, as was previously proposed, and is instead evocative of a more exotic quantum spin liquid-like ground state.