We have measured the electrical resistivity ρ and the thermal conductivity κ of Sr14-xAxCu24O41(A = Ca and La) single crystals. The Arrhenius plot of In ρ vs T-1 gives two kinds of activation energy with a boundary temperature Tρ. The activation energy at T < Tρ 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 κph, κspin and κhole due to phonons, spins and holes, respectively. The κph exhibits a small peak at ∼ 30 K in every direction of every single-crystal. The contribution of κspin 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 > Tρ to decrease with increasing x(Ca).
|Number of pages||5|
|Journal||Journal of Low Temperature Physics|
|Publication status||Published - Dec 1 1999|
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Materials Science(all)
- Condensed Matter Physics