Evidence for Ballistic Thermal Conduction in the One-Dimensional S=1/2 Heisenberg Antiferromagnetic Spin System Sr2CuO3

We have measured the thermal conductivity of the one-dimensional (1D) S=1/2 Heisenberg antiferromagnetic spin system of Sr2Cu1-xPdxO3 single crystals including nonmagnetic impurities of Pd2+. It has been found that the mean free path of spinons along the 1D spin chain at low temperatures is very close to the average length of finite spin chains between spin defects estimated from the magnetic susceptibility measurements. This proves that the thermal conduction due to spinons at low temperatures in Sr2CuO3 is ballistic as theoretically expected [Zotos et al.: Phys. Rev. Lett. 55 (1997) 11029]

Growth of Bi-(Sr,La)-Cu-O single crystals with the floating-zone technique

The TSFZ method has been used to grow crystals of the Bi-oxide superconductor of the Bi-n = 1 structure. The investigated compositions are Bi2Sr2CuO6+z, Bi2.3Sr1.7CuO6+z, and Bi2+xSr1.6- LayCuO6+z (x+y = 0.4). Except for the stoichiometric composition, the TSFZ experiments yield plate-like crystals of the superconducting R-phase. Superconductivity was only present in La substituted crystals and the TC could be changed by annealing procedures. A maximum TC = 29 K is found for Bi2.0Sr1.6La0.4CuO6+z

Growth and propertis of M2-xCexCu04+d single crystals

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