Naturally tuned quantum critical point in the S=1 kagomé YCa3(VO)3(BO3)4

Although S=1/2 kagomé systems have been intensely studied theoretically, and within the past decade been realized experimentally, much less is known about the S=1 analogs. While the theoretical ground state is still under debate, it has been found experimentally that S=1 kagomé systems either order at low temperatures or enter a spin glass state. In this work, YCa3(VO)3(BO3)4 (YCVBO) is presented, with trivalent vanadium. Owing to its unusual crystal structure, the metal-metal bonding is highly connected along all three crystallographic directions, atypical of other kagomé materials. Using neutron scattering it is shown that YCVBO fails to order down to at least 50 mK and exhibits broad and dispersionless excitations. B11 NMR provides evidence of fluctuating spins at low temperatures while dc magnetization shows critical scaling that is also observed in systems near a quantum critical point such as Herbertsmithite, despite its insulating nature and S=1 magnetism. The evidence shown indicates that YCVBO is naturally tuned to be a quantum disordered magnet in the limit of T=0 K.