Unusual states in the Heisenberg model with competing interactions

A phase diagram of the anisotropic Heisenberg model with competition between the nearest and the next-to-nearest neighbour exchange interactions is investigated by using the bosonisation scheme. An instability leading to a spontaneous dimerisation is found. The new 'superfluid' phases with both nonzero, though nonnominal, Z-magnetisation and broken symmetry in the XY-plane are detected in the anisotropic case.