Towards Device Applications
Whereas the progress in understanding of the interface physics between oxides with antagonistic long range order [e.g. ferromagnetism (F) and high temperature superconductivity (HTS)] has been made during past years [1,2], little is known about feasibility of fabrication oxide HTS-F-HTS Josephson junctions and subsequent exploration of their properties. In general, it is well established that competitive interactions between F and HTS layers in HTS-F superlattices lead to a suppression of superconductivity and magnetism. This effect usually manifests as strong reduction of the superconducting transition temperature of HTS layers and the Curie temperature (TC) of the ferromagnetic layers with decreasing thicknesses of the constituents. In the ongoing work we show that an ultra-thin LCMO ferromagnetic layer with thickness of few unit cells can be grown in between of two thick YBCO superconducting layers. In particular, the ferromagnetic transition temperature is found to be TC~250K which is close to the bulk value. This opens up the way to investigate electronic transport across thin ferromagnetic layer with possible perspectives (i) to fabricate oxide HTS-F-HTS Josephson junctions and (ii) to understand in details the proximity effects in oxides HTS-F-HTS heterostructures with strong electron correlations. The main difficulty in accomplishing this goal is a technological one and arises from the length scale required to obtain a supercurrent across the F layer. Since the length scale on which such a current decays is given by the superconducting coherence length, an according realization for HTS could not be achieved so far. The samples that are prepared in our group can possibly close this gap (see Fig. 5).
Fig.1: The magnetization versus magnetic field M(H) measured at T=5K (blue) and T=100K (red) for the sample structure YBCO-50 nm/tLCMO/YBCO-50nm (tLCMO is thickness of LCMO layer) The external applied field was perpendicular to the CuO2 planes in all cases. The left panel (a and c) refers to samples grown on STO (110), where the right panel (b and d) to samples grown on STO (001). The upper panels corresponds to shows the tLCMO=2nm, the lower to the tLCMO=1nm.
References
[1] Magnetism at the interface between ferromagnetic and superconducting oxides. Chakhalian J., et al. Nature Physics 2, 244 (2006).
[2] Orbital reconstruction and covalent bonding at an oxide interface. Chakhalian J., et al. Science 318, 1114 (2007).
[3] Step towards a ferromagnetic Josephson junction in YBCO/LCMO heterostructures. Soltan S., et al. to be submitted to Appl. Phys. Lett (2012).