Thermal conductivity in the frustrated two-leg spin- ladder system BiCu₂PO₆

We have measured temperature and magnetic-field dependences of the thermal conductivity of single crystals of the frustrated two-leg spin-ladder system BiCu₂PO₆ in magnetic fields up to 14 T. It has been found that the temperature dependence of the thermal conductivity along every principal crystallographic axis shows two peaks in zero field but that the magnitude of the thermal conductivity along the b-axis parallel to spin ladders, κ_b, is significantly larger than those of the thermal conductivity along the a-axis, κ_a, and along the c- axis, κ_c, at high temperatures above 7 K. These results suggest that the thermal conductivity due to spins probably exists only in κ_b. Furthermore, it has been found that both magnetic-field dependences of κ_a and κ_b at 3 K show kinks at ∼ 7 T and ∼ 10 T, where the spin state may change.