Date: Monday 12 September 2016

Time: 16.00 hours

Place: Lecture Room E, Lorentzweg 1, Delft

Host: Herre van der Zant

Speaker: Jens Paaske, Niels Bohr Institute, Copenhagen, Denmark

Title: Self-organized topological superconductivity in Yu-Shiba-Rusinov chains

Motivated by recent experiments, we study lattices of magnetic adatoms exchange coupled to the surface of a conventional s-wave superconductor. We show that a variety of collective magnetic and electronic phases emerge in this system, due to the interplay between ferromagnetism and superconductivity. In particular, an adatom chain on a bulk (2d or 3d) superconductor can order into a magnetic spiral state leading to, and stabilized by, the opening of a topological superconducting gap within the band of YSR states induced by the adatoms. The spiral wave-vector increases sharply as the YSR energy is lowered from the quasiparticle continuum, due to a strong spin-spin exchange interaction mediated through the band of sub-gap YSR states. As the YSR band enters the topological phase, the wave-vector exhibits a peak and is thereafter driven down towards ferromagnetism due to YSR state double-exchange. We provide the range of YSR energies and adatom spacing where these phases exist for adatoms on a 3d, or 2d  superconductor. The magnetic ordering within a 2d YSR lattice is also explored.

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