Frustrated quantum critical theory of putative spin-liquid phenomenology in 6H-B-Ba3NiSb2O9

A recently discovered material, 6H-B-Ba3NiSb2O9 was found to display unusual low-temperature phenomenology, interpreted as a quantum spin liquid with spin S = 1 on a triangular lattice. We study a spin S = 1 quantum exchange model on an AB stacked triangular lattice near its quantum paramagnet-to-spiral magnet transition, driven by easy-plane single-ion anisotropy. We demonstrate that the frustrated inter- and intra-layer exchange interactions induce contour lines of low energy excitations that lead to a broad crossover regime of linear-temperature dependence of the specific heat. Based on this and a variety of other predictions, we argue that the observed phenomenology can be understood in terms of a conventional picture of a proximity to this frustrated critical point.