Ising-nematic order in the bilinear-biquadratic model for the iron pnictides

Ergueta, Patricia Bilbao; Nevidomskyy, Andriy H.

doi:10.1103/physrevb.92.165102

Cited by 14 publications

(18 citation statements)

References 88 publications

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“…1 indicates, the CAFM phase dominates for small J 3 , provided |K 1 | is not too large, while for sufficiently negative K 1 we observe the appearance of either the FQ or the (π,π) Néel phase. This is due to the fact that in the absence of K 2 , a negative biquadratic coupling K 1 renormalizes the NN Heisenberg interaction, making the (π,π) correlations stronger [28,39]. Since the Néel phase has not been observed in either iron pnictides or chalcogenides, our calculations support the conclusion that K 2 must be present and negative.…”

Section: Phase Diagramssupporting

confidence: 74%

“…Regarding the microscopic origin of these couplings, the large negative K 1 was found in the so-called spin crossover model by Chaloupka and Khaliullin [38]. A large negative K 1 also naturally arises within the Kugel-Khomskii-type models when the orbitals order inside the nematic phase [39].…”

Section: Phase Diagramsmentioning

confidence: 98%

“…Our starting point is the strong-coupling approach, justified in the limit when Coulomb interaction U is considerably larger than the electron hopping t. Although the iron chalcogenides are not charge insulating systems, the strong-coupling approaches have been successfully used to elucidate many aspects of these materials, from the nature of electron nematicity [26,28,39] and effects of orbital selectivity [53][54][55][56], to the origin of the superconducting pairing [57][58][59][60][61]. One of the justifications for using the strong-coupling approach is the large fluctuating iron moment observed in inelastic neutron scattering (M 2 eff ≈ 5μ 2 B per Fe ion [62]), which is difficult to obtain in the weak-coupling scenario from considering only the electrons near the Fermi surface.…”

Section: Discussionmentioning

confidence: 99%

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Unified spin model for magnetic excitations in iron chalcogenides

Ergueta¹,

Hu²,

Nevidomskyy³

2017

Phys. Rev. B

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Recent inelastic neutron scattering (INS) measurements on FeSe and Fe(Te 1−x Se x ) have sparked intense debate over the nature of the ground state in these materials. Here we propose an effective bilinear-biquadratic spin model, which is shown to consistently describe the evolution of low-energy spin excitations in FeSe, both under applied pressure and upon Se/Te substitution. The phase diagram, studied using a combination of variational mean-field, flavor-wave calculations and density-matrix renormalization group (DMRG), exhibits a sequence of transitions between the columnar antiferromagnet common to the iron pnictides, the nonmagnetic ferroquadrupolar phase attributed to FeSe, and the double-stripe antiferromagnetic order known to exist in Fe 1+y Te. The calculated spin structure factor in these phases mimics closely that observed with INS in the Fe(Te 1−x Se x ) series. In addition to the experimentally established phases, the possibility of incommensurate magnetic order is also predicted.

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Section: Phase Diagramssupporting

confidence: 74%

Section: Phase Diagramsmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Unified spin model for magnetic excitations in iron chalcogenides

Ergueta¹,

Hu²,

Nevidomskyy³

2017

Phys. Rev. B

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“…Semiclassical calculations for this model find various magnetic ordered phases to interpret the observed magnetic orders in iron pnictides and FeTe 36,42,[47][48][49][50][51][52] . Recent mean-field studies propose an antiferroquadrupolar (AFQ) state for FeSe 39,40 , which exhibits a nematic order accompanied by the quadrupolar fluctuations at wave vector q = (0, π)/(π, 0).…”

Section: Introductionmentioning

confidence: 99%

Possible nematic spin liquid in spin-1 antiferromagnetic system on the square lattice: Implications for the nematic paramagnetic state of FeSe

et al. 2017

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The exotic normal state of iron chalcogenide superconductor FeSe, which exhibits vanishing magnetic order and possesses an electronic nematic order, triggered extensive explorations of its magnetic ground state. To understand its novel properties, we study the ground state of a highly frustrated spin-1 system with bilinearbiquadratic interactions using unbiased large-scale density matrix renormalization group. Remarkably, with increasing biquadratic interactions, we find a paramagnetic phase between Néel and stripe magnetic ordered phases. We identify this phase as a candidate of nematic quantum spin liquid by the compelling evidences, including vanished spin and quadrupolar orders, absence of lattice translational symmetry breaking, and a persistent non-zero lattice nematic order in the thermodynamic limit. The established quantum phase diagram natually explains the observations of enhanced spin fluctuations of FeSe in neutron scattering measurement and the phase transition with increasing pressure. This identified paramagnetic phase provides a new possibility to understand the novel properties of FeSe.

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“…1. The large negative K 1 is also expected from the spin crossover model by Chaloupka and Khaliullin [39], which also incorporates the FQ and CAFM phases; and large |K 1 | also naturally arises within the KugelKhomskii type models when the orbitals order inside the nematic phase [40]. No other purely quadrupolar phases were found; in particular, the AFQ(π, 0)/(0, π) phase, expected to be realized for positive K 2 [29] turns out to be unstable to the admixture of the magnetic moment, resulting in a mixed magnetic or quadrupolar state with 0 < | S i | < 1 (gray region in Fig.…”

mentioning

confidence: 95%

Spin Ferroquadrupolar Order in the Nematic Phase of FeSe

Wang

Nevidomskyy

2016

Phys. Rev. Lett.

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We provide evidence that spin ferroquadrupolar (FQ) order is the likely ground state in the nonmagnetic nematic phase of stoichiometric FeSe. By studying the variational mean-field phase diagram of a bilinearbiquadratic Heisenberg model up to the 2nd nearest neighbor, we find the FQ phase in close proximity to the columnar antiferromagnet commonly realized in iron-based superconductors; the stability of FQ phase is further verified by the density matrix renormalization group. The dynamical spin structure factor in the FQ state is calculated with flavor-wave theory, which yields a qualitatively consistent result with inelastic neutron scattering experiments on FeSe at both low and high energies. We verify that FQ can coexist with C 4 breaking environments in the mean-field calculation, and further discuss the possibility that quantum fluctuations in FQ act as a source of nematicity. Superconductivity in the iron-based superconductors [1,2] is widely recognized to have spin fluctuations at its origin [3,4], as it develops after the suppression of columnar antiferromagnetism (CAFM) by doping or applied pressure on the parent compounds [5][6][7][8]. The CAFM phase is characterized by the magnetic Bragg peaks at wave vectors Q 1,2 = (π, 0)/(0, π) in the one-iron Brillouin zone, seen ubiquitously in different families of the iron pnictides and chalcogenides [5,9,10]. The discovery of superconductivity in stoichiometric FeSe thus came as a surprise, because the long-range magnetic order is conspicuously absent in this material [11][12][13][14][15][16]. Another important feature, universally observed across different families of iron-based superconductors, is the appearance of an electronic nematic phase [17][18][19][20], which spontaneously breaks the lattice C 4 rotational symmetry. Usually, nematicity appears in close proximity to magnetism above the Néel temperature; however, in FeSe, the nematic phase appears without any accompanying magnetism and coexists with superconductivity [12][13][14][15]. It is thus important to understand the origin of this nonmagnetic nematic phase, in particular, to gain insight into its effect on superconductivity.It turns out that magnetic order can be induced by applying hydrostatic pressure to FeSe [12][13][14]. It has also been suggested based on ab initio calculations that the nonmagnetic phase in FeSe lies in close proximity to the CAFM phase [21][22][23]. Further evidence of proximity to long-range magnetic order comes from inelastic neutron scattering (INS) experiments, which found large spectral weight at wave vectors Q 1,2 [24][25][26][27]. Two natural questions arise: In the theoretical phase diagram, is there a nonmagnetic phase that neighbors on the CAFM? And, furthermore, how does such a nonmagnetic phase give rise to nematicity?In an attempt to answer these questions, several theoretical scenarios have been proposed for nonmagnetic ground states that may appear as a result of frustration: a nematic quantum paramagnet [28], a spin quadrupolar state with wave vectors Q 1,2...

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Ising-nematic order in the bilinear-biquadratic model for the iron pnictides

Cited by 14 publications

References 88 publications

Unified spin model for magnetic excitations in iron chalcogenides

Unified spin model for magnetic excitations in iron chalcogenides

Possible nematic spin liquid in spin-1 antiferromagnetic system on the square lattice: Implications for the nematic paramagnetic state of FeSe

Spin Ferroquadrupolar Order in the Nematic Phase of FeSe

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