Surface instability in nodal noncentrosymmetric superconductors

Timm, Carsten; Rex, Sybille; Brydon, P. M. R.

doi:10.1103/physrevb.91.180503

Cited by 14 publications

(21 citation statements)

References 54 publications

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“…It was realized that requiring a full superconducting gap was not required to generate edge states 229,243,286,287,[293][294][295][296][297]304 . For pairing states with the same symmetry as the crystal (s-wave-like), these states appeared in the predominantly spin-triplet case.…”

Section: B Nodal Noncentrosymmetric Superconductorsmentioning

confidence: 99%

Superconductivity and spin–orbit coupling in non-centrosymmetric materials: a review

Smidman¹,

Salamon²,

Yuan³

et al. 2017

Rep. Prog. Phys.

486

451

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In non-centrosymmetric superconductors, where the crystal structure lacks a centre of inversion, parity is no longer a good quantum number and an electronic antisymmetric spin-orbit coupling (ASOC) is allowed to exist by symmetry. If this ASOC is sufficiently large, it has profound consequences on the superconducting state. For example, it generally leads to a superconducting pairing state which is a mixture of spin-singlet and spin-triplet components. The possibility of such novel pairing states, as well as the potential for observing a variety of unusual behaviors, led to intensive theoretical and experimental investigations. Here we review the experimental and theoretical results for superconducting systems lacking inversion symmetry. Firstly we give a conceptual overview of the key theoretical results. We then review the experimental properties of both strongly and weakly correlated bulk materials, as well as two dimensional systems. Here the focus is on evaluating the effects of ASOC on the superconducting properties and the extent to which there is evidence for singlet-triplet mixing. This is followed by a more detailed overview of theoretical aspects of non-centrosymmetric superconductivity. This includes the effects of the ASOC on the pairing symmetry and the superconducting magnetic response, magneto-electric effects, superconducting finite momentum pairing states, and the potential for non-centrosymmetric superconductors to display topological superconductivity.

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Section: B Nodal Noncentrosymmetric Superconductorsmentioning

confidence: 99%

Superconductivity and spin–orbit coupling in non-centrosymmetric materials: a review

Smidman¹,

Salamon²,

Yuan³

et al. 2017

Rep. Prog. Phys.

486

451

View full text Add to dashboard Cite

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“…These materials lack inversion symmetry and are characterized by strong antisymmetric spin-orbit coupling (SOC), which induces a non-trivial topology for the electronic band structure 27 . This leads to the existence of helical Majorana modes, zero-energy flat-bands 15,24,28 and arc surface states 29,30 .…”

Section: Introductionmentioning

confidence: 99%

Edge currents as a probe of the strongly spin-polarized topological noncentrosymmetric superconductors

et al. 2018

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Recently the influence of antisymmetric spin-orbit coupling has been studied in novel topological superconductors such as half-Heuslers and artificial hetero-structures. We investigate the effect of Rashba and/or Dresselhaus spin-orbit couplings on the band structure and topological properties of a two-dimensional noncentrosymetric superconductor. For this goal, the topological helical edge modes are analyzed for different spin-orbit couplings as well as for several superconducting pairing symmetries. To explore the transport properties, we examine the response of the spin-polarized edge states to an exchange field in a superconductor-ferromagnet heterostructure. The broken chiral symmetry causes the uni-directional currents at opposite edges.

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“…Upon further cooling, the observed zero-bias peak splits into two 38,39 , which is interpreted as a sign of spontaneous TRS breaking 40 . This was examined by several MF studies [4][5][6][7][8][9] , which found that for attractive interactions the order parameter develops imaginary s-wave components near the boundary, while for repulsive interactions edge ferromagnetism (FM) is induced.…”

Section: Introductionmentioning

confidence: 99%

“…Ss, 03.65.vf, 71.27.+a, 74.20.Rp, 74.50.+r Introduction: The discovery of topological insulators 1,2 has led to the insight that nontrivial band topologies can give rise to exotic surface states [1][2][3] . Particularly interesting are topological flat-band surface states, since their large density of states enhances correlation effects [4][5][6][7][8][9][10][11][12][13][14][15] . Surface states with a (nearly) flat dispersion can occur both in topological semimetals [15][16][17] and in nodal topological superconductors (SCs) [18][19][20][21] .…”

mentioning

confidence: 99%

Edge instabilities of topological superconductors

2016

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Nodal topological superconductors display zero-energy Majorana flat bands at generic edges. The flatness of these edge bands, which is protected by time-reversal and translation symmetry, gives rise to an extensive ground-state degeneracy. Therefore, even arbitrarily weak interactions lead to an instability of the flat-band edge states towards time-reversal and translation-symmetry-broken phases, which lift the ground-state degeneracy. We examine the instabilities of the flat-band edge states of dxy-wave superconductors by performing a mean-field analysis in the Majorana basis of the edge states. The leading instabilities are Majorana mass terms, which correspond to coherent superpositions of particle-particle and particle-hole channels in the fermionic language. We find that attractive interactions induce three different mass terms. One is a coherent superposition of imaginary s-wave pairing and current order, and another combines a charge-density-wave and finite-momentum singlet pairing. Repulsive interactions, on the other hand, lead to ferromagnetism together with spin-triplet pairing at the edge. Our quantum Monte Carlo simulations confirm these findings and demonstrate that these instabilities occur even in the presence of strong quantum fluctuations. We discuss the implications of our results for experiments on cuprate high-temperature superconductors.PACS numbers: 02.70. Ss, 03.65.vf, 71.27.+a, 74.20.Rp, 74.50.+r Introduction: The discovery of topological insulators 1,2 has led to the insight that nontrivial band topologies can give rise to exotic surface states [1][2][3] . Particularly interesting are topological flat-band surface states, since their large density of states enhances correlation effects [4][5][6][7][8][9][10][11][12][13][14][15] . Surface states with a (nearly) flat dispersion can occur both in topological semimetals [15][16][17] and in nodal topological superconductors (SCs) [18][19][20][21] . However, only in the latter systems is the flatness of the surface states protected by symmetry [21][22][23] . That is, time-reversal symmetry (TRS), particle-hole symmetry (PHS), and translation symmetry ensure that the surface states are pinned at zero energy, resulting in a band of neutral Majorana fermions.These Majorana bands exist in one-or two-dimensional regions of the surface Brillouin zone, which are bounded by the projections of the superconducting nodes. Hence, the number of zero-energy surface states grows linearly or quadratically with the length of the system, leading to a diverging density of states at zero energy and an extensive ground-state degeneracy. Since this is in violation with the third law of thermodynamics, even arbitrarily weak interactions cause a singular perturbation of the Majorana flat bands, giving rise to novel symmetry-broken states at the surface [8][9][10][11][12][13][14][15]24 . Due to the flat-band character and the low dimensionality of the boundary, these symmetry-broken states are subject to strong fluctuations. Therefore, it is necessary to use metho...

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Surface instability in nodal noncentrosymmetric superconductors

Cited by 14 publications

References 54 publications

Superconductivity and spin–orbit coupling in non-centrosymmetric materials: a review

Superconductivity and spin–orbit coupling in non-centrosymmetric materials: a review

Edge currents as a probe of the strongly spin-polarized topological noncentrosymmetric superconductors

Edge instabilities of topological superconductors

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