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

We show that the spin chain/ladder compound La 3 Sr 3 Ca 8 Cu 24 O 41 is an insulator with hopping transport along the chains. In the temperature range 35– 280 K, dc conductivity sigma dc (T) follows Mott’ s law of variable-range hopping conduction ; the frequency dependence has the form sigma( n, T)= sigma dc (T) +A(T) n^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.

spin ladders ; variable-range hopping ; dielectrci response ; optical response

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