Enhancing the Proximity Effect in Superconductor / Ferromagnet Devices

Tuesday 28 September 2010 at 4pm

CNRS Bât E, conference room "Louis Weil" on 3rd floor

Jason ROBINSON (University of Cambridge, UK)

In a ferromagnet which is coupled to a superconductor, a spin-singlet supercurrent can exist but will rapidly decay over a few nanometers [1, 2]. Enhancements to this proximity effect are predicted to occur in more exotic systems in which some inhomogeneous magnetism is present [3]. In such systems, a supercurrent of electron pairs with a finite spin-projection (a spin-triplet supercurrent) may arise with a substantially longer coherence length than spin-singlet paired electrons in a ferromagnet. Evidence of a spin-triplet proximity effect in superconductor-ferromagnet systems has been indirectly observed by measuring supercurrents or substantial diminutions in the resistance across a range of complex magnetic barriers [4].

    This presentation focuses on the properties of exotic Josephson junctions with various types of inhomogeneous magnetic barriers. In particular, reports of a substantially enhanced superconducting proximity effect in Fe/Cr/Fe [5] and Ho/Co/Ho [6] barriers will be discussed.

[1]    T Kontos et al., Phys. Rev. Lett. 86, 304 (2001); V Ryazanov et al., Phys. Rev. Lett. 86,     2427 (2001); Y. Blum et al., Phys. Rev. Lett. 89, 187004 (2002).

[2]     A Buzdin, Rev. Mod. Phys. 77, 935 (2005).

[3]     F Bergeret, A Volkov, K Efetov, Rev. Mod. Phys. 77, 1321 (2005); M Houzet, A Buzdin,     Phys. Rev. B 76, 060504(R) (2007).

[4]     R Keizer et al., Nature 439, 825 (2006); M Anwar et al., arXiv/1003.4446 (2010); I Sosnin     et al., Phys. Rev. Lett. 96, 157002 (2006); J Wang et al., Nat. Phys. 6, 389 (2010); T     Khaire et al., Phys.Rev. Lett. 104, 137002 (2010); D Sprungmann et al., arXiv/1003.2082     (2010).

[5]     J Robinson et al., Phys. Rev. Lett. 104, 207001 (2010).

[6]     J Robinson, J Witt, M Blamire, Science 1189246 (2010).