The electronic properties of interfaces and surfaces of high-Tc superconductors play a decisive role for the understanding and design of numerous experiments, as well as for most applications of these materials. Remarkably, the transport properties of interfaces in the high-Tc compounds differ systematically from those involving conventional superconductors, an effect which has been studied in great detail by numerous groups. Nevertheless, a comprehensive description of the mechanisms controlling the electronic properties of interfaces in high-Tc superconductors is still in development.
Here we point out the important influences of the dx2-y2-symmetry component of the superconducting order parameter, and of space-charge layers associated with band bending at the interfaces [1-3]. These space charge layers can be altered to optimize the interface properties, just as they can be in semiconductors or in oxides like doped BaTiO3 or ZnO. We have applied this understanding to grain boundaries in the high-Tc cuprates and established for the first time a model which provides a comprehensive description of their behavior and successfully predicted ways for their improvement. Utilizing this model we have been able to overcome a long- standing challenge of high-Tc superconductivity and to enhance the critical current densities and to decrease the normal state resistivities of the grain boundaries by large factors [4]. In the presentation it will be pointed out that comparable band bending phenomena are also expected to occur in non- superconducting oxide materials with non-negligible electronic screening lengths, e.g. in the CMR-manganates [2].
References
[1] H. Hilgenkamp, J. Mannhart and B. Mayer, Phys. Rev. B 53,
14 586 (1996).
[2] J. Mannhart and H. Hilgenkamp, Materials Science and
Engineering B 56, 77 (1998).
[3] H. Hilgenkamp and J. Mannhart, Appl. Phys. Lett. 73, 265
(1998).
[4] A. Schmehl et al., Europhys. Lett. 47, 110 (1999).
Project supported by the BMBF (project 6918/1).