Variable-range hopping conductivity in the copper-oxygen chains of La₃Sr₃Ca₈Cu₂₄O₄₁

We show that the spin chain/ladder compound La₃Sr₃Ca₈Cu₂₄O₄₁ is an insulator with hopping transport along the chains. In the temperature range 35–280 K, dc conductivity σ_dc(T) follows Mott’s law of variable-range hopping conduction; the frequency dependence has the form σ(ν, T) = σ_dc(T) + A(T)ν^s, where s ≈ 1. The conduction mechanism changes from variable-range hopping to nearest-neighbor hopping around T_c = 300 K. The chain array thus behaves as a one-dimensional disordered system. Disorder is due to random structural distortions of chains induced by irregular coordination of the La/Sr/Ca ions.