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We have investigated the effect of disorder on the normal state resistiviy of underdoped and optimally doped YBa2Cu3O7-δ single crystals down to low temperature by suppressing superconductivity with high magnetic field up to 58 Teslas.
Electron irradiation is used to introduce point defects in a controlled manner in the CuO2 planes of the samples. These defects are found analogous to Zn substitution on the copper planar site [1]. This allowed us to study the Tc depression and the evolution of the normal state transport properties with increasing defect content. Low-T upturns of resistivity are observed in YBCO7 and YBCO6.6 for large defect content. In YBCO6.6, we have previously shown that, at high T, the defect contribution to the resistivity initially increases linearly with the defect content [2].
We report here results on several irradiated samples (YBCO7 with Tc ∼ 3.5K and two crystals of YBCO6.6 with Tc ∼ 30K and 3K) for which we were able to completely suppress superconductivity by magnetic field and to follow the temperature dependence of the resistivity down to 0.5K. In all these samples, the defect contribution to the resistivity is well described by a -ln(T) behaviour as T is lowered. However we observe a saturation of resistivity below ~ 4K in YBCO7 whereas the ln(T) behavior is seen down to the lowest temperature investigated in YBCO6.6.
These results will be discussed in terms of a Kondo-like spin flip scattering term, as suggested by the results obtained on magnetic properties induced by spin less defects such as Li [3].
[1] A. Legris, F. Rullier-Albenque et al, J. Phys. I France 3,1605 (1993). [2] F. Rullier-Albenque, H. Alloul and R. Tourbot, Phys. Rev. Lett. 87, 157001 (2001). [3] J. Bobroff, et al, Phys. Rev. Lett. 83, 4381 (1999) |