Possible quadrupolar nematic phase in the frustrated spin chain LiCuSbO4 : An NMR investigation

The frustrated one-dimensional quantum magnet ${\mathrm{LiCuSbO}}₄$ is a rare realization of the ${J}₁\ensuremath{-}{J}₂$ spin chain model with an easily accessible saturation field, formerly estimated at 12 T. Exotic multipolar nematic phases were theoretically predicted in such compounds just below the saturation field, but without unambiguous experimental observation so far. In this paper we present extensive experimental research on the compound in a wide temperature (30 mK to 300 K) and field (0--13.3 T) range by muon spin rotation ($\ensuremath{\mu}\mathrm{SR}$), $⁷\mathrm{Li}$ nuclear magnetic resonance (NMR), and magnetic susceptibility (SQUID). $\ensuremath{\mu}\mathrm{SR}$ experiments in zero magnetic field demonstrate the absence of long-range 3D ordering down to 30 mK. Together with former heat capacity data [Dutton et al., Phys. Rev. Lett. 108, 187206 (2012)], magnetic susceptibility measurements suggest a short-range-correlated vector chiral phase in the field range 0--4 T. At the intermediate-field values (5--12 T), the system enters a 3D-ordered spin density wave phase with $0.75\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_B$ per copper site at lowest temperatures (125 mK), estimated by NMR. At still higher field, the magnetization is found to be saturated above 13 T where the spin lattice ${T}₁^{\ensuremath{-}1}$ relaxation reveals a spin gap estimated at 3.2(2) K. We narrow down the possibility of observing a multipolar nematic phase to the range 12.5--13 T.