Abstract
We have measured the electrical resistivity ρ and the thermal conductivity κ of Sr 14−x A x Cu 24 O 41(A = Ca and La) single crystals. The Arrhenius plot of ln ρ vs T −1 gives two kinds of activation energy with a boundary temperature T ρ . The activation energy at T < T ρ is in approximate agreement with the spin gap in the ladder estimated from the NMR measurements, suggesting that holes in the ladder are paired and localized at T < Tρ. The observed κ has been analyzed to be composed of κ ph , κ spin and κ hole due to phonons, spins and holes, respectively. The κ ph exhibits a small peak at ∼ 30 K in every direction of every single-crystal. The contribution of κ spin is observed along the c-axis except for x(Ca) ≥ 6, and the spin gap, which corresponds to the spin excitation from spin-singlet to spin-triplet, has been estimated to be ∼ 420 K. For x(Ca) ≥ 6, the spin gap, which corresponds to the destruction of spin-singlet pairs i. e. the dissociation of hole pairs, has been estimated from κ along the c-axis at T > T ρ to decrease with increasing x(Ca).
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Kudo, K., Ishikawa, S., Noji, T. et al. Spin Gap and Hole Pairing of Sr14−x A x Cu24O41(A = Ca and La) Single Crystals Studied by the Electrical Resistivity and Thermal Conductivity. Journal of Low Temperature Physics 117, 1689–1693 (1999). https://doi.org/10.1023/A:1022588421579
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DOI: https://doi.org/10.1023/A:1022588421579