Helical order in one-dimensional magnetic atom chains and possible emergence of Majorana bound states

Younghyun Kim; Meng Cheng; Bela Bauer; Roman M. Lutchyn; S. Das Sarma

doi:10.1103/physrevb.90.060401

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arXiv · 1401.7048

Helical order in one-dimensional magnetic atom chains and possible emergence of Majorana bound states

Younghyun Kim·Meng Cheng·Bela Bauer·Roman M. Lutchyn·S. Das Sarma

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Abstract

We theoretically obtain the phase diagram of localized magnetic impurity spins arranged in a one-dimensional chain on top of a one- or two-dimensional electron gas with Rashba spin-orbit coupling. The interactions between the spins are mediated by the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism through the electron gas. Recent work predicts that such a system may intrinsically support topological superconductivity when a helical spin-density wave is formed in the spins, and superconductivity is induced in the electron gas. We analyze, using both analytical and numerical techniques, the conditions under which such a helical spin state is stable in a realistic situation in the presence of disorder. We show that it becomes unstable towards the formation of (anti) ferromagnetic domains if the disorder in the impurity spin positions $δR$ becomes comparable with the Fermi wave length. We also examine the stability of the helical state against Gaussian potential disorder in the electronic system using a diagrammatic approach. Our results suggest that in order to stabilize the helical spin state, and thus the emergent topological superconductivity, a sufficiently strong Rashba spin-orbit coupling, giving rise to Dzyaloshinskii-Moriya interactions, is required.

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Younghyun Kim, Meng Cheng, Bela Bauer, Roman M. Lutchyn, S. Das Sarma. 2014-07-29. Helical order in one-dimensional magnetic atom chains and possible emergence of Majorana bound states. https://doi.org/10.1103/physrevb.90.060401

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