Theory of spin excitations in a quantum spin-nematic state

Smerald, Andrew; Shannon, Nic

doi:10.1103/physrevb.88.184430

Cited by 104 publications

(143 citation statements)

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“…It is also interesting to note that the same phenomenology of linearly-dispersing excitations, with a vanishing spectral weight at long wavelengths, is encountered in quantum spin nematics 78 . In this case, low-energy spin fluctuations are controlled by a time derivative of the underlying nematic order parameter 79 , and so vanish for ω → 0.…”

Section: Seeing the Light : Photons And Inelastic Neutron Scatteringmentioning

confidence: 99%

Seeing the light: Experimental signatures of emergent electromagnetism in a quantum spin ice

2012

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The "spin ice" state found in the rare earth pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7 offers a beautiful realisation of classical magnetostatics, complete with magnetic monopole excitations. It has been suggested that in "quantum spin ice" materials, quantum-mechanical tunnelling between different ice configurations could convert the magnetostatics of spin ice into a quantum spin liquid which realises a fully dynamical, latticeanalogue of quantum electromagnetism. Here we explore how such a state might manifest itself in experiment, within the minimal microscopic model of a such a quantum spin ice. We develop a lattice field theory for this model, and use this to make explicit predictions for the dynamical structure factor which would be observed in neutron scattering experiments on a quantum spin ice. We find that "pinch points", which are the signal feature of a classical spin ice, fade away as a quantum ice is cooled to its zero-temperature ground state. We also make explicit predictions for the ghostly, linearly dispersing magnetic excitations which are the "photons" of this emergent electromagnetism. The predictions of this field theory are shown to be in quantitative agreement with Quantum Monte Carlo simulations at zero temperature.

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Section: Seeing the Light : Photons And Inelastic Neutron Scatteringmentioning

confidence: 99%

Seeing the light: Experimental signatures of emergent electromagnetism in a quantum spin ice

2012

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“…However, there is no Bragg peak as the dynamical spin structure factor S (q, ω) shown in Fig. 3(b) has a vanishing spectral weight (∝ |q|) at q = 0, ω = 0 because of the conservation of time reversal symmetry in quadrupolar states [50,51,53,54]. In Fig.…”

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“…A possible way to visualize such "ghost" modes is by applying a magnetic field: the degeneracy of the two flavors will be lifted, and one of the Goldstone modes acquires a gap and a visible spectral weight [53,54], as we demonstrate in Ref. [41].…”

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“…The quadrupolar orders can also be measured by Raman scattering, which is able to couple to spin and quadrupolar operators by tuning light polarization and incoming light frequency, thus showing qualitatively different features for magnetic and quadrupolar phases [55]. More direct evidence can be gained from the quadrupolar structure factor, which should exhibit Bragg peaks at the ordering wave vector [53], and, in principle, can be measured by resonant inelastic x-ray scattering experiments [56,57].…”

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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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“…В этом случае ферромагнитный порядок становится энергетически невыгодным, и в системе реализуется нематическое упорядочение, опре-деляемое квадрупольными параметрами порядка. Необ-ходимо отметить, что нематический порядок не является парамагнитным, поскольку диагональные компоненты тензора квадрупольных моментов не равны друг дру-гу [34].…”

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Динамические И Статические Свойства Негейзенберговского Магнетика Со Сложной Межионной Анизотропией

Гореликов¹,

Космачев²,

Кривцова³

et al. 2017

Физика Твердого Тела

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Исследовано влияние анизотропного обменного взаимодействия на фазовые состояния негейзенберговского ферромагнетика со спином магнитного иона S=1. Показано, что в зависимости от соотношений параметров анизотропного обменного взаимодействия, а также их знака в системе реализуется либо двухосный негейзенберговский магнетик, либо изинговский. Изучены динамические свойства системы в окрестностях ориентационных фазовых переходов, а также фазовых переходов по модулю магнитного момента. Построены фазовые диаграммы системы при различных соотношениях материальных параметров. Работа выполнена при финансовой поддержке РФФИ (проекты N 16-02-00069а и N 16-32-00098 мол\_а). DOI: 10.21883/FTT.2017.03.44159.289

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Theory of spin excitations in a quantum spin-nematic state

Cited by 104 publications

References 80 publications

Seeing the light: Experimental signatures of emergent electromagnetism in a quantum spin ice

Seeing the light: Experimental signatures of emergent electromagnetism in a quantum spin ice

Spin Ferroquadrupolar Order in the Nematic Phase of FeSe

Динамические И Статические Свойства Негейзенберговского Магнетика Со Сложной Межионной Анизотропией

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