Triplet supercurrents in clean and disordered half-metallic ferromagnets

M. Eschrig; T. Löfwander

doi:10.1038/nphys831

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arXiv · cond-mat/0612533

Triplet supercurrents in clean and disordered half-metallic ferromagnets

M. Eschrig·T. Löfwander

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Abstract

Interfaces between materials with differently ordered phases present unique opportunities to study fundamental problems in physics. One example is the interface between a singlet superconductor and a half-metallic ferromagnet, where Cooper pairing occurs between electrons with opposite spin on one side, while the other displays 100% spin polarisation. The recent surprising observation of a supercurrent through half-metallic CrO_2 therefore requires a mechanism for conversion between unpolarised and completely spin polarised supercurrents. Here we suggest a conversion mechanism based on electron spin precession together with triplet pair rotation at interfaces with broken spin-rotation symmetry. In the diffusive limit the triplet supercurrent is dominated by inter-related odd-frequency s-wave and even-frequency p-wave pairs. In the crossover to the ballistic limit additional symmetry components become relevant. The interface region exhibits a superconducting state of mixed-spin pairs with highly unusual symmetry properties that opens up new perspectives for exotic Josephson devices.

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M. Eschrig, T. Löfwander. 2011-09-21. Triplet supercurrents in clean and disordered half-metallic ferromagnets. https://doi.org/10.1038/nphys831

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