The effect of oxygen doping on the transition lines in BSCCO

To further characterize the extended vortex phase diagram consisting of a first-order melting transition and a second-order glass transitions, we studied the dependence of these transition lines on the oxygen over-doping of the sample, δ [1]. The main effect of oxygen over-doping is to increase the coupling between the superconducting layers. This stiffens the pancake vortex stacks, thereby reducing the sample anisotropy and enhancing the elasticity of the vortex matter [2]. In addition, the excess oxygen atoms act as added point defects [3].

We found that the glass transition obeys a surprisingly simple anisotropy-scaling law which neglects the effect of disorder altogether [4]. By fitting the doping-dependent phase diagrams to those calculated from a theoretical model [5], we found that although defect density is known to increase with over-doping, the overall effect of disorder decreases due to the reduced anisotropy.

Doping dependence of the first-  and second-order transition lines in the thermodynamic vortex phase diagram in BSCCO.

Rescaling the high-temperature part of the melting lines according to Bm~ε2 collapses the second-order glass lines, though fails for the disorder-induced inverse-melting.


Additional information

  1. Interplay of anisotropy and disorder in the doping-dependent melting and glass transitions of vortices in Bi2Sr2CaCu2O8+δ
    H. Beidenkopf, T. Verdene, Y. Myasoedov, H. Shtrikman, E. Zeldov, B. Rosenstein, D. Li, and T. Tamegai
    Phys. Rev. Lett. 98, 167004 (2007).
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    B. Khaykovich, E. Zeldov, D. Majer, T. W. Li, P. H. Kes, and M. Konczykowski 
    Phys. Rev. Lett. 76, pp. 2555-2558 (1996).
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    T. W. Li, , A. A. Menovsky, J. J. M. Franse and P. H. Kes
    Physica C 257, 179 (1996).
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    Phys. Rev. Lett. 68, 875 (1992).
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    D. Li, B. Rosenstein, and V. Vinokur
    J. Supercond. Novel Mag. 19, 369 (2007)