Is $\mathrm{YbMgGaO_4}$ a spin liquid or a disorder-driven state?

In $\mathrm{YbMgGaO_4}$ (effective $S = 1/2$ Yb3+ doublets on a triangular lattice, nearest-neighbor exchange of order 0.1 meV, random Mg/Ga site mixing), determine whether the $T \to 0$ ground state is a quantum spin liquid with fractionalized spinons, a random-singlet (valence-bond glass) state, or a spin glass. An answer names the state with evidence that discriminates the three: the field and temperature scaling of $C$ and $\chi$, ac-susceptibility freezing below 0.1 K, and whether the neutron continuum is reproduced by a disordered model without fractionalization.

Neutron spectra, ac susceptibility below 0.1 K and thermal conductivity on the same crystals, compared quantitatively with simulations of the fitted anisotropic exchange model that include the measured distribution of random couplings.