Collapse of susceptibility and nontrivial spin dynamics in the hyperhoneycomb magnet β-Li2IrO3 under high pressure

We present high-pressure (2 GPa) Li7 nuclear magnetic resonance (NMR) measurements on single crystals of the hyperhoneycomb 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.