Magnetic state of the geometrically frustrated quasi-one-dimensional spin system Cu₃Mo₂O₉ studied by thermal conductivity

We have measured the thermal conductivity of the geometrically frustrated quasi-one-dimensional spin system Cu₃Mo₂O₉ in magnetic fields. A contribution of the thermal conductivity due to spins has been observed in the thermal conductivity along the spin chains. The thermal conductivity due to phonons, κ_phonon, has been found to decrease by the application of a magnetic field, which has been explained as being due to the reduction in the spin gap originating from the spin-singlet dimers. Moreover, it has been found that κ_phonon increases with increasing field in high fields above ∼7T at low temperatures. This suggests the existence of a novel field-induced spin state and is discussed in terms of the possible spin-chirality ordering in a frustrated Mott insulator.