The emergent behavior of spin liquids that are born out of geometrical frustration makes them an intriguing state of matter. We show that in the quantum kagome antiferromagnet ${\mathrm{ZnCu}}_3({\mathrm{OH})}_6{\mathrm{SO}}_4$ several different correlated yet fluctuating states exist. By combining complementary local-probe techniques with neutron scattering, we discover a crossover from a critical regime into a gapless spin-liquid phase with decreasing temperature. An additional unconventional instability of the latter phase leads to a second, distinct spin-liquid state that is stabilized at the lowest temperatures. We advance such complex behavior as a feature common to different frustrated quantum magnets.

• Received 22 October 2015
• Revised 15 January 2016

DOI:https://doi.org/10.1103/PhysRevB.93.060405