Spectral properties of quasiparticle excitations induced by magnetic moments in superconductors

Salkola, M. I.; Balatsky, A. V.; Schrieffer, J. R.

doi:10.1103/physrevb.55.12648

Cited by 247 publications

(327 citation statements)

References 20 publications

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“…Magnetic moments bind Yu-Shiba-Rusinov subgap states [9][10][11][12][13] with wavefunctions decaying as e −r/ξ r 1/2 . Therefore the Shiba states have strong overlap with a large number of neighbouring sites when a < ξ, where ξ is the superconducting coherence length and a is the lattice constant of the magnetic atoms.…”

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Topological Superconductivity and High Chern Numbers in 2D Ferromagnetic Shiba Lattices

2015

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Inspired by the recent experimental observation of topological superconductivity in ferromagnetic chains, we consider a dilute 2D lattice of magnetic atoms deposited on top of a superconducting surface with a Rashba spin-orbit coupling. We show that the studied system supports a generalization of px + ipy superconductivity and that its topological phase diagram contains Chern numbers higher than ξ/a ( 1), where ξ is the superconducting coherence length and a is the distance between the magnetic atoms. The signatures of nontrivial topology can be observed by STM spectroscopy in finite-size islands.

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Topological Superconductivity and High Chern Numbers in 2D Ferromagnetic Shiba Lattices

2015

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“…Often impurities are regarded as a nuisance that spoils the properties of a clean system and complicates the understanding of its properties. However, impurities are in many instances essential to obtain desirable physical effects and can be used as unique atomic-scale probes of the ground state of the host system [2][3][4][5][6][7][8][9][10]. The study of the effect of impurities in superconductors has been a very active field of research [10].…”

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Impurity-Induced Bound States in Superconductors with Spin-Orbit Coupling

et al. 2015

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We study the effect of strong spin-orbit coupling (SOC) on bound states induced by impurities in superconductors. The presence of spin-orbit coupling breaks the SU(2)-spin symmetry and causes the superconducting order parameter to have generically both singlet (s-wave) and triplet (p-wave) components. We find that in the presence of SOC the spectrum of Yu-Shiba-Rusinov (YSR) states is qualitatively different in s-wave and p-wave superconductor, a fact that can be used to identify the superconducting pairing symmetry of the host system. We also predict that in the presence of SOC the spectrum of the impurity-induced bound states depends on the orientation of the magnetic moment S of the impurity and, in particular, that by changing the orientation of S the fermion-parity of the lowest energy bound state can be tuned. We then study the case of a dimer of magnetic impurities and show that in this case the YSR spectrum for a p-wave superconductor is qualitatively very different from the one for an s-wave superconductor even in the limit of vanishing SOC. Our predictions can be used to distinguish the symmetry of the order parameter and have implications for the Majorana proposals based on chains of magnetic atoms placed on the surface of superconductors with strong spin-orbit coupling [1]. PACS numbers: 73.20.Hb, 75.70.Tj, The presence of impurities is almost always unavoidable in condensed matter systems. Often impurities are regarded as a nuisance that spoils the properties of a clean system and complicates the understanding of its properties. However, impurities are in many instances essential to obtain desirable physical effects and can be used as unique atomic-scale probes of the ground state of the host system [2-10]. The study of the effect of impurities in superconductors has been a very active field of research [10]. In an s-wave superconductor magnetic impurities cause the formation of bound states, the Yu-ShibaRusinov (YSR) states [11][12][13]. There has been a significant interest in the properties of YSR states due to theoretical proposals suggesting that a chain of magnetic impurities placed on the surface of a superconductor (SC) would be a very robust, self-tuning, system that should exhibit non-abelian, Majorana, states [14][15][16][17][18]. In these proposals the bound states induced by the chain of magnetic impurities form an impurity band with non-trivial topological character. More recently it has been pointed out that the presence of Rashba spin-orbit coupling (SOC) should facilitate the realization of a topological impurity band of YSR states. [1,[19][20][21]. On the surface, due to the lack of inversion symmetry, some amount of Rashba SOC will be present. Therefore, for the systems considered to realize a topological band of YSR states the presence of Rashba SOC is both unavoidable and beneficial. This assessment has very recently been confirmed by the experimental results presented in Ref. 1, that show some evidence of the presence of Majorana modes at the end of a chain of Fe atoms place...

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“…Bulk superconductors with arbitrary magnetic impurity concentrations are gapless [38]. This is because, in addition to the extended impurity band of hybridized subgap Yu-Shiba-Rusinov states [39][40][41][42][43], there can exist rare configurations of lumped impurities that induce Lifshitz tails to the density of states (DOS) at all subgap energies [44].…”

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confidence: 99%

Topological superconductivity and anti-Shiba states in disordered chains of magnetic adatoms

2016

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Regular arrays of magnetic atoms on a superconductor provide a promising platform for topological superconductivity. In this work, we study the effects of disorder in these systems, focusing on vacancies realized by missing magnetic atoms. We develop approaches that allow treatment of ferromagnetic dense chains as well as long-range hopping ferromagnetic and helical Shiba chains at arbitrary subgap energies. Vacancies in magnetic chains play an analogous role to magnetic impurities in a clean s-wave superconductor. A single vacancy in a topological chain gives rise to a low-lying "anti-Shiba" state below the band edge of a regular magnetic chain. Proliferation of the anti-Shiba band formed by a finite density of hybridized vacancy states leads to deterioration of the topological phase, which exhibits unusual fragility in a particular parameter region in dilute chains. We also consider local fluctuation in the Shiba coupling and discuss how vacancy states could contribute to experimental verification of topological superconductivity.

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Spectral properties of quasiparticle excitations induced by magnetic moments in superconductors

Cited by 247 publications

References 20 publications

Topological Superconductivity and High Chern Numbers in 2D Ferromagnetic Shiba Lattices

Topological Superconductivity and High Chern Numbers in 2D Ferromagnetic Shiba Lattices

Impurity-Induced Bound States in Superconductors with Spin-Orbit Coupling

Topological superconductivity and anti-Shiba states in disordered chains of magnetic adatoms

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