SPIN-DISORDERED STATES IN THE ANTIFERROMAGNETIC HEISENBERG-MODEL ON THE TRIANGULAR LATTICE

To gain a starting point for an explanation of a recent experiment by Takeda et al. on NaTiO2, the triangular-lattice antiferromagnetic Heis enberg model with S = 1/2 is investigated by a fermion mean-field theo ry. We find two self-consistent solutions that describe a spin disorde red state with a finite excitation gap. Both phases are consistent wit h the experiment and thereby should be regarded as promising candidate s for the physical state realized in NaTiO2.