Spin reorientation driven by the interplay between spin-orbit coupling and Hund's rule coupling in iron pnictides

Christensen, Morten H.; Kang, Jian; Andersen, Brian M.; Eremin, I.; Fernandes, Rafael M.

doi:10.1103/physrevb.92.214509

Cited by 65 publications

(101 citation statements)

References 68 publications

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“…Consequently, it has become the focus of many recent first principle reports to reveal what parameters are causing the sudden reordering of the single-Q C 2 structure into this novel double-Q structure and how this new phase hosts superconductivity. 12,[15][16][17][18][19] Currently, several different proposed models predict the observed C 4 but they do so through different mechanisms which range from expanded itinerant mean field models to impurity scattering stabilization to spin-orbit coupling driven spin anisotropies. 15,17,18 The different models invoke varying assumptions about the underlying physics in these materials and necessarily predict different, sometimes subtlety so, manifestations of the C 4 phase.…”

Section: Introductionmentioning

confidence: 99%

Observation of the magnetic C4 phase in Ca1−xNaxFe2As2

et al. 2017

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Since its discovery in 2014 the magnetic tetragonal C4 phase has been identified in a growing number of hole-doped '122' Fe-based superconducting compounds. Exhibiting a unique double-Q magnetic structure and a strong competition with both superconducting and magnetic order parameters, the C4 phase and the conditions of its formation are of significant interest to understanding the fundamental mechanisms in these materials. Particularly, separating the importance of direct changes to the relative size of hole and electron pockets at the Fermi surface (achieved via charge doping) from the role of structural changes due to differences of ionic radii of dopants is useful to determine the underlying parameter which causes the C4 instability. Here, we report the discovery of the C4 phase in a fourth member of the hole-doped '122' materials Ca1−xNaxFe2As2 (0.20 ≤ x ≤ 0.50) as determined from neutron and X-ray powder diffraction studies. The maximum of the C4 dome is observed at x = 0.44 with a re-entrant temperature Tr= 52K and an extent of ∆x ∼ 0.07 in composition. It is observed that for a range of compositions within the C4 dome (0.40 ≤ x ≤ 0.42) there is a second re-entrance (Tr 2 < Tr) where the AFM-C2 phase is recovered -a feature previously only seen in Ba1−xKxFe2As2. A phase diagram is presented for Ca1−xNaxFe2As2 and compared to the other Na + -doped '122's' -A1−xNaxFe2As2 with A = Ba, Sr and Ca. The structural parameters for these three systems are compared and the importance of the 'chemical pressure' due to changing the A-site ion (A = Ba, Sr, Ca) is discussed.

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Section: Introductionmentioning

confidence: 99%

Observation of the magnetic C4 phase in Ca1−xNaxFe2As2

et al. 2017

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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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“…Several microscopic mechanisms have been proposed to explain their origin [4,5,[25][26][27][28][29][30][31][32][33][34][35]. However, they generally suffer from two drawbacks.…”

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confidence: 99%

“…The latter is in contradiction with the sizable spin-orbit coupling (SOC) observed in these systems [36], whose 100 K energy scale is comparable to the typical magnetic transition temperature. As a result, the spin anisotropies induced by SOC [29], which are experimentally observed by neutron scattering and NMR [37][38][39][40][41][42][43][44], cannot be neglected near the magnetic transition. More broadly, it is difficult to attribute the observed near degeneracy between the C 2 and C 4 phases only to material-specific properties, since this behavior is often seen close to the putative quantum critical point [see schematic Fig.…”

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Emergent Magnetic Degeneracy in Iron Pnictides due to the Interplay between Spin-Orbit Coupling and Quantum Fluctuations

et al. 2018

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Recent experiments in iron pnictide superconductors reveal that, as the putative magnetic quantum critical point is approached, different types of magnetic order coexist over a narrow region of the phase diagram. Although these magnetic configurations share the same wave vectors, they break distinct symmetries of the lattice. Importantly, the highest superconducting transition temperature takes place close to this proliferation of near-degenerate magnetic states. In this Letter, we employ a renormalization group calculation to show that such a behavior naturally arises due to the effects of spin-orbit coupling on the quantum magnetic fluctuations. Formally, the enhanced magnetic degeneracy near the quantum critical point is manifested as a stable Gaussian fixed point with a large basin of attraction. Implications of our findings to the superconductivity of the iron pnictides are also discussed. Disciplines Condensed Matter Physics | Metallurgy | Physics CommentsThis article is published as Christensen, Morten H., Peter P. Orth, Brian M. Andersen, and Rafael M. Fernandes. "Emergent magnetic degeneracy in iron pnictides due to the interplay between spin-orbit coupling and quantum fluctuations." Physical Review Letters 121, no. 5 (2018) Recent experiments in iron pnictide superconductors reveal that, as the putative magnetic quantum critical point is approached, different types of magnetic order coexist over a narrow region of the phase diagram. Although these magnetic configurations share the same wave vectors, they break distinct symmetries of the lattice. Importantly, the highest superconducting transition temperature takes place close to this proliferation of near-degenerate magnetic states. In this Letter, we employ a renormalization group calculation to show that such a behavior naturally arises due to the effects of spin-orbit coupling on the quantum magnetic fluctuations. Formally, the enhanced magnetic degeneracy near the quantum critical point is manifested as a stable Gaussian fixed point with a large basin of attraction. Implications of our findings to the superconductivity of the iron pnictides are also discussed.

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Spin reorientation driven by the interplay between spin-orbit coupling and Hund's rule coupling in iron pnictides

Cited by 65 publications

References 68 publications

Observation of the magnetic C4 phase in Ca1−xNaxFe2As2

Observation of the magnetic C4 phase in Ca1−xNaxFe2As2

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

Emergent Magnetic Degeneracy in Iron Pnictides due to the Interplay between Spin-Orbit Coupling and Quantum Fluctuations

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