Charge redistribution in high-Tc superconductors due to structural defects or interfaces is known to be crucial for electronic applications as the band structure is modified on a local scale. In order to investigate these effects in more detail, the interface of YBa2Cu3O7 (YBCO) with the semiconductor GaAs is considered. It is started from ab initio calculations for the normal state YBCO-metal and for the GaAs semiconductor. For that purpose, the Density Functional Theory (DFT) together with the Full-Potential Linearized Augmented Plane Wave (FP-LAPW) method is used as it is implemented in the Wien2k code. The GaAs interface layer is found to be metallic, a result that is of intrinsic interest.

Investigating and synthesizing new spintronic materials has a great practical importance due to their application in future information technology and electronic devices. Among all proposed materials, semiconductors doped with magnetic ions (V, Cr, Mn, Fe, Co, and Ni) or prepared as a hybrid structure of magnetic elements with a semiconductor exhibit the most promising properties. The (Ga, Mn)As heterostructures have opened a completely new method to combine magnetism with charge transport in well-known semiconductor device structures (Samara et al. (1990); and Wronka (2007)).

Surfaces of superconductors and superconductor-semiconductor interfaces play an important role in technological device applications. Their physical and chemical characteristics are responsible for the interesting properties and, consequently, the subject is now-a-days a very active area of research. Some delicate points have been put forward in the literature on this subject. For example in superconductor-metal interfaces where due to large dielectric constants and small carrier (Mannhart and Hilgenkamp (1998)) densities, electronic transport in wires and tapes from high-Tc materials is seriously affected by structural defects and interfaces (Hahn et al. (1994); and Hilgenkamp and Mannhart (2003))). Moreover, the specific contact resistivity of YBa2Cu3O7 (YBCO)—metal thin films is determined by details of the contact geometry (Komissinskii et al. (2001)) and the transport in micron-sized YBCO—metal heterojunctions also depends on the orientation of the YBCO crystallographic axes with respect to the direction of the current flow (Schwingenschlögl and Schuster (2007a)). Unexpected high specific resistivities of YBCO—Au interfaces, 10_4 cm2 to 10_3 cm2 at low temperatures (Xu and Ekin (2004)), presumably result from local distortions at the interface.

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