Seminar by Annica Black-Schaffer (Uppsala University) – University of Copenhagen

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Seminar by Annica Black-Schaffer (Uppsala University)

Title:

Topological Superconductors: From a mixed chirality state to persistent currents due to spin-orbit coupling

Abstract:

Topological superconductors have lately received a lot of attention. New topological superconducting states have been discovered and the physical properties of these states have also been investigated. In this talk I will present the results from two recent projects where we have discovered a new topological mixed chirality phase and established the existence of persistent currents due to spin-orbit coupling.

First, I will show that a mixed chirality d-wave superconducting state exists in the coexistence region between antiferromagnetism and superconductivity in strongly correlated honeycomb materials. This state has chiral d+id-wave symmetry in one Dirac valley, but d−id-wave symmetry in the other valley and hosts two counter-propagating edge states, protected in the absence of intervalley scattering. A first-order topological phase transition, with no bulk gap closing, separates the chiral d-wave state at small magnetic moments from the mixed chirality d-wave phase.

Secondly, I will show that persistent currents are generated around magnetic impurities and ferromagnetic islands proximity-coupled to superconductors with finite spin-orbit coupling. For point magnetic impurities the current is carried by the induced Yu-Shiba-Rusinov (YSR) subgap states. For ferromagnetic islands, the topologically protected edge states give rise to spin-polarized edge currents. However, the total persistent current flows in opposite direction to what is expected from the dispersion relation of these edge states. In the vicinity of the topological phase transition, the current generally increases dramatically. Furthermore, the currents are orthogonal to the local spin polarization and can thus be probed by measuring the spin-polarized local density of states.