Topological surface states in paramagnetic and antiferromagnetic iron pnictides

Lau, Andy K. S.; Timm, Carsten

doi:10.1103/physrevb.88.165402

Cited by 18 publications

(32 citation statements)

References 35 publications

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“…In fact, it is expected that for any given discrete space-group symmetry, there is a distinct topological classification of band insulators and fully gapped superconductors, and that each of these space-groupsymmetry-protected topological states can be characterized in terms of an associated crystalline topological number. * chiu7@phas.ubc.ca † a.schnyder@fkf.mpg.de Parallel to these developments, the concept of topological band theory has been extended to semimetals with Fermi points or Fermi lines, and nodal superconductors with point nodes or line nodes [26,[32][33][34][35][36][37][38][39][40][41][42][43][44]. Although a global topological number cannot be defined for these gapless systems, it is nevertheless possible to determine their topological characteristics and the stability of their Fermi points or Fermi lines in terms of momentum-dependent topological numbers.…”

Section: Introductionmentioning

confidence: 98%

Classification of reflection-symmetry-protected topological semimetals and nodal superconductors

2014

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While the topological classification of insulators, semimetals, and superconductors in terms of nonspatial symmetries is well understood, less is known about topological states protected by crystalline symmetries, such as mirror reflections and rotations. In this work, we systematically classify topological semimetals and nodal superconductors that are protected, not only by nonspatial (i.e., global) symmetries, but also by a crystal reflection symmetry. We find that the classification crucially depends on (i) the codimension of the Fermi surface (nodal line or point) of the semimetal (superconductor), (ii) whether the mirror symmetry commutes or anticommutes with the nonspatial symmetries, and (iii) how the Fermi surfaces (nodal lines or points) transform under the mirror reflection and nonspatial symmetries. The classification is derived by examining all possible symmetry-allowed mass terms that can be added to the Bloch or Bogoliubov-de Gennes Hamiltonian in a given symmetry class and by explicitly deriving topological invariants. We discuss several examples of reflection-symmetry-protected topological semimetals and nodal superconductors, including topological crystalline semimetals with mirror Z 2 numbers and topological crystalline nodal superconductors with mirror winding numbers.

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Section: Introductionmentioning

confidence: 98%

Classification of reflection-symmetry-protected topological semimetals and nodal superconductors

2014

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“…The particular arrangement of the yz and zx orbitals arises because under a 90 degree rotation the two orbitals transform as |xz → |yz and |yz → −|xz [250]. Consequence of this singular C 4 symmetry is a non trivial topology manifested in the vorticity two of the Γ pocket [144,250,251].…”

Section: Anisotropy and The Spin-orbital-lattice Entanglementmentioning

confidence: 99%

Magnetic interactions in iron superconductors: A review

Bascones

Valenzuela

Calderón

2015

Comptes Rendus. Physique

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High temperature superconductivity in iron pnictides and chalcogenides emerges when a magnetic phase is suppressed. The multi-orbital character and the strength of correlations underlie this complex phenomenology, involving magnetic softness and anisotropies, with Hund's coupling playing an important role. We review here the different theoretical approaches used to describe the magnetic interactions in these systems. We show that taking into account the orbital degree of freedom allows us to unify in a single phase diagram the main mechanisms proposed to explain the (π, 0) order in iron pnictides: the nesting-driven, the exchange between localized spins, and the Hund induced magnetic state with orbital differentiation. Comparison of theoretical estimates and experimental results helps locate the Fe superconductors in the phase diagram. In addition, orbital physics is crucial to address the magnetic softness, the doping dependent properties, and the anisotropies.

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“…Restoring φ 0 introduces a dispersion to the flat-band edge states, which remain within the bulk gap 21 . With the onset of superconductivity, these edge-bands disperse into the ABS 20 within the superconducting gap formed at the Fermi pockets.…”

Section: Two Orbital Modelmentioning

confidence: 99%

“…With (π, 0)-SDW the edge bands become spin-split ( Fig. 3 (a)) 21 . For a particular transverse momentum, subfigures (b)-(c) of Fig.…”

Section: Spin-density-wave Phasementioning

confidence: 99%

“…Emergence of ABS at the edges of pnictides has also been proposed as a signature of the extended s-wave superconductivity [17][18][19][20] . On another front, it has been argued that in the normal phase, the non-trivial topological character of the electronic band structure of pnictides can lead to the development of edge states which are spin-degenerate in the paramagnetic phase and split into spin-polarized edge bands in the SDW phase 21 . In this paper we consider the coexistence of SDW and extended s-wave superconductivity and show that further unconventional types of superconducting pairing, known as odd-frequency pairing, should develop on the edges.…”

Section: Introductionmentioning

confidence: 99%

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Odd-frequency pairing in the edge states of superconducting pnictides in the coexistence phase with antiferromagnetism

et al. 2018

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In some of the Ferro-pnictide materials, spin density wave order coexists with superconductivity over a range of doping and temperature. In this paper, we show that odd-frequency pairing emerges on the edges of pnictides in such a coexistence phase. In particular, the breaking of spin-rotation symmetry by spin density wave and translation symmetry by the edge can lead to the development of odd-frequency spin-triplet Cooper pairing. In this case, the odd-frequency pairing has even parity components, which are immune to disorder. Our results show that pnictides are a natural platform to realize odd frequency superconductivity, which has been mainly searched for in heterostructures of magnetic and superconducting materials. The emergence of odd-frequency pairing on the edges and in the defects can be potentially detected in magnetic response measurements. arXiv:1802.08268v2 [cond-mat.supr-con]

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Topological surface states in paramagnetic and antiferromagnetic iron pnictides

Cited by 18 publications

References 35 publications

Classification of reflection-symmetry-protected topological semimetals and nodal superconductors

Classification of reflection-symmetry-protected topological semimetals and nodal superconductors

Magnetic interactions in iron superconductors: A review

Odd-frequency pairing in the edge states of superconducting pnictides in the coexistence phase with antiferromagnetism

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