Successive Phase Transitions And Extended Spin-Excitation Continuum In The S=1/2 Triangular-Lattice Antiferromagnet Ba3cosb2o9

Using magnetic, thermal, and neutron measurements on single-crystal samples, we show that Ba3CoSb2O9 is a spin-1/2 triangular-lattice antiferromagnet with the c axis as the magnetic easy axis and two magnetic phase transitions bracketing an intermediate up-up-down phase in magnetic field applied along the c axis. A pronounced extensive neutron-scattering continuum above spin-wave excitations, observed below T-N, implies that the system is in close proximity to one of two spin-liquid states that have been predicted for a 2D triangular lattice. DOI: 10.1103/PhysRevLett.109.267206