Microscopically derived Ginzburg-Landau theory for magnetic order in the iron pnictides

Brydon, P. M. R.; Schmiedt, Jacob; Timm, Carsten

doi:10.1103/physrevb.84.214510

Cited by 52 publications

(80 citation statements)

References 72 publications

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“…While most of the iron-based superconductors exhibit an antiferromagnetic stripe order 2 , bulk FeSe appears to be paramagnetic 10 . This has led others to investigate various magnetic configurations to compete with the C 2 stripe order (alternatively, collinear or single-q), particularly C 4 (alternatively, tetragonal or double-q) orders, which have been given various labels; orthomagnetic (OM) and spin charge order (SCO) [11][12][13][14] , C 4 spin density wave (SDW) 15 , spin vortex crystal (SVC) and charge-spin density wave (CSDW) [16][17][18] . The orthomagnetic order is equivalent to the spin vortex crystal, while the spin charge order is equivalent to the charge-spin density wave.…”

Section: Introductionmentioning

confidence: 99%

Stabilizing the spin vortex crystal phase in two-dimensional iron-based superconductors

2017

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We present an investigation of the magnetic structure for iron-based superconductors (FeSCs) when inversion symmetry is broken, such as in substrate-supported monolayers or in the presence of a c-axis electric field. We perform group-, mean-field-, and density-functional-theoretic analyses on a model system of monolayer iron selenide (FeSe) on a strontium titanate (SrTiO3(001)) substrate. Our group-and mean-field-theoretic calculations are more generally applicable to thin films of the rest of the 11 (e.g., FeSe) family of iron-based superconductors, as well as to thin films of the 111 (e.g., LiFeAs) and 1111 (e.g., LaOFeAs) families, as these all belong to the same space group. We find that in systems with a collinear antiferromagnetic phase in bulk, when inversion symmetry is broken the transition is instead into a "spin vortex crystal" phase, and that a further phase transition can occur at a lower temperature in some circumstances. The spin vortex crystal is a C4 symmetric magnetic phase which is related to this parent C2 symmetric collinear antiferromagnetic (stripe) phase which is ubiquitous among the iron-based superconductors.

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Section: Introductionmentioning

confidence: 99%

Stabilizing the spin vortex crystal phase in two-dimensional iron-based superconductors

2017

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“…Such a second transition is highly unlikely in an orbital scenario because the breaking of symmetry of Q X and Q Y is a precondition for a magnetic transition to occur. However, it is known that such a phase is a possible solution of itinerant magnetic models for certain combinations of electronic interactions and/or Fermi surface geometries 8,[27][28][29] . By going beyond our earlier Ginzburg-Landau analysis, we now show that the phase diagram is much richer than previously thought and that the C 4 phase becomes energetically favourable at higher doping levels, particularly in the range of phase coexistence with superconductivity 29 .…”

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confidence: 99%

Magnetically driven suppression of nematic order in an iron-based superconductor

et al. 2014

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A theory of superconductivity in the iron-based materials requires an understanding of the phase diagram of the normal state. In these compounds, superconductivity emerges when stripe spin density wave (SDW) order is suppressed by doping, pressure or atomic disorder. This magnetic order is often pre-empted by nematic order, whose origin is yet to be resolved. One scenario is that nematic order is driven by orbital ordering of the iron 3d electrons that triggers stripe SDW order. Another is that magnetic interactions produce a spin-nematic phase, which then induces orbital order. Here we report the observation by neutron powder diffraction of an additional fourfold-symmetric phase in Ba 1 À x Na x Fe 2 As 2 close to the suppression of SDW order, which is consistent with the predictions of magnetically driven models of nematic order.

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“…All in all, for three dimensions, we will have only one single first-order transition line in the phase diagram for any given β. Therefore there are no preemptive Ising transitions any more, as in the SS case [5][6][7]9,39,[42][43][44][45][46][47][48]. Representative phase diagrams in 3D are shown in Fig.…”

Section: B Three Dimensionsmentioning

confidence: 99%

Emergent Ising degrees of freedom above a double-stripe magnetic ground state

Zhang

Flint

2017

Phys. Rev. B

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Double-stripe magnetism [ Q = ( π / 2 , π / 2 ) ] has been proposed as the magnetic ground state for both the iron-telluride and BaTi 2 Sb 2 O families of superconductors. Double-stripe order is captured within a J 1 − J 2 − J 3 Heisenberg model in the regime J 3 ≫ J 2 ≫ J 1 . Intriguingly, besides breaking spin-rotational symmetry, the ground-state manifold has three additional Ising degrees of freedom associated with bond ordering. Via their coupling to the lattice, they give rise to an orthorhombic distortion and to two nonuniform lattice distortions with wave vector ( π , π ) . Because the ground state is fourfold degenerate, modulo rotations in spin space, only two of these Ising bond order parameters are independent. Here, we introduce an effective field theory to treat all Ising order parameters, as well as magnetic order, and solve it within a large-N limit. All three transitions, corresponding to the condensations of two Ising bond order parameters and one magnetic order parameter are simultaneous and first order in three dimensions, but lower dimensionality, or equivalently weaker interlayer coupling, and weaker magnetoelastic coupling can split the three transitions, and in some cases allows for two separate Ising phase transitions above the magnetic one. Double-stripe magnetism [Q = (π/2,π/2)] has been proposed as the magnetic ground state for both the iron-telluride and BaTi 2 Sb 2 O families of superconductors. Double-stripe order is captured within a J 1 -J 2 -J 3 Heisenberg model in the regime J 3 J 2 J 1 . Intriguingly, besides breaking spin-rotational symmetry, the ground-state manifold has three additional Ising degrees of freedom associated with bond ordering. Via their coupling to the lattice, they give rise to an orthorhombic distortion and to two nonuniform lattice distortions with wave vector (π,π). Because the ground state is fourfold degenerate, modulo rotations in spin space, only two of these Ising bond order parameters are independent. Here, we introduce an effective field theory to treat all Ising order parameters, as well as magnetic order, and solve it within a large-N limit. All three transitions, corresponding to the condensations of two Ising bond order parameters and one magnetic order parameter are simultaneous and first order in three dimensions, but lower dimensionality, or equivalently weaker interlayer coupling, and weaker magnetoelastic coupling can split the three transitions, and in some cases allows for two separate Ising phase transitions above the magnetic one. Disciplines Condensed Matter Physics

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Microscopically derived Ginzburg-Landau theory for magnetic order in the iron pnictides

Cited by 52 publications

References 72 publications

Stabilizing the spin vortex crystal phase in two-dimensional iron-based superconductors

Stabilizing the spin vortex crystal phase in two-dimensional iron-based superconductors

Magnetically driven suppression of nematic order in an iron-based superconductor

Emergent Ising degrees of freedom above a double-stripe magnetic ground state

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