A spin triplet supercurrent through the half-metallic ferromagnet CrO2

In general, conventional superconductivity should not occur in a ferromagnet, though it has been seen in iron under pressure. Moreover, theory predicts that the current is always carried by pairs of electrons in a spin singlet state, so conventional superconductivity decays very rapidly when in contact with a ferromagnet, which normally prohibits the existence of singlet pairs. It has been predicted that this rapid spatial decay would not occur when spin triplet superconductivity could be induced in the ferromagnet. Here we report a Josephson supercurrent through the strong ferromagnet CrO2, from which we infer that it is a spin triplet supercurrent. Our experimental setup is different from those envisaged in the earlier predictions, but we conclude that the underlying physical explanation for our result is a conversion from spin singlet to spin triplets at the interface. The supercurrent can be switched with the direction of the magnetization, analogous to spin valve transistors, and therefore could enable magnetization-controlled Josephson junctions.Comment: 14 pages, including 3 figure

Optimization of RF- and DC-sputtered NbTiN films for integration with Nb-based SIS junctions

NbTiN is one of the most promising materials for use in the tuning circuits of Nb-based SIS mixers for operating frequencies above the gap frequency of Nb (/spl ap/700 GHz). We examine the properties of NbTiN films obtained using an unbalanced sputtering source in both RF and DC operating regimes. It is found that the properties of NbTiN films are strongly affected by the total pressure of the sputtering process. Films obtained under lower pressures have higher compressive stresses and lower resistivities. The best NbTiN films are obtained by DC sputtering and have a transition temperature of 14.4 K, a resistivity of 90 /spl mu//spl Omega//spl middot/cm at 20 K, and a compressive stress of -1 GPa. Films with a resistivity of 110 /spl mu//spl Omega//spl middot/cm at 20 K and a compressive stress of -0.5 GPa have been successfully used as a stripline material for Nb/Al-AlO/sub x//Nb SIS junctions on fused quartz substrates.NbTiN is one of the most promising materials for use in the tuning circuits of Nb-based SIS mixers for operating frequencies above the gap frequency of Nb (/spl ap/700 GHz). We examine the properties of NbTiN films obtained using an unbalanced sputtering source in both RF and DC operating regimes. It is found that the properties of NbTiN films are strongly affected by the total pressure of the sputtering process. Films obtained under lower pressures have higher compressive stresses and lower resistivities. The best NbTiN films are obtained by DC sputtering and have a transition temperature of 14.4 K, a resistivity of 90 /spl mu//spl Omega//spl middot/cm at 20 K, and a compressive stress of -1 GPa. Films with a resistivity of 110 /spl mu//spl Omega//spl middot/cm at 20 K and a compressive stress of -0.5 GPa have been successfully used as a stripline material for Nb/Al-AlO/sub x//Nb SIS junctions on fused quartz substrates