Spin dynamics and disorder effects in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>S</mml:mi><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac></mml:mrow></mml:math>kagome Heisenberg spin-liquid phase of kapellasite

Kermarrec, E.; Zorko, A.; Bert, F.; Colman, R. H.; Koteswararao, B.; Bouquet, F.; Bonville, P.; Hillier, A. D.; Amato, A.; Tol, Johan van; Ozarowski, Andrew; Wills, A. S.; Mendels, P.

doi:10.1103/physrevb.90.205103

Cited by 53 publications

(49 citation statements)

References 57 publications

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“…After intense theoretical research activity on quantum spin liquids in the late 1980's and 1990's due to their intimate relation with high-temperature superconductivity [2], interest in QSL has recently regained momentum because of possible applications in quantum computing [3]. More strikingly, however, enormous experimental progress in synthetization and characterization of actual spin liquid candidate materials has catapulted the field to an unprecedented stage of maturity in this century (see and references therein).A highly interesting, recently synthesized QSL candidate material is the so-called kapellasite [14][15][16][17]: X-ray diffraction on powder samples of this strong Mott insulator indicates geometrically perfect, uncoupled twodimensional kagome layers of spin S = 1/2 Cu ions, despite some on-site Cu/Zn dilution. Muon spectroscopy shows the absence of frozen moments, inelastic neutron scattering exhibits a continuum of excitations (mimicking a spinon continuum), and the plateau in 1/T 1 of NMR measurements confirms a fluctuating behavior down to 20 mK.…”

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confidence: 99%

“…More strikingly, however, enormous experimental progress in synthetization and characterization of actual spin liquid candidate materials has catapulted the field to an unprecedented stage of maturity in this century (see Refs. [4][5][6][7][8][9][10][11][12][13][14][15][16] and references therein).…”

mentioning

confidence: 99%

“…A highly interesting, recently synthesized QSL candidate material is the so-called kapellasite [14][15][16][17]: X-ray diffraction on powder samples of this strong Mott insulator indicates geometrically perfect, uncoupled twodimensional kagome layers of spin S = 1/2 Cu ions, despite some on-site Cu/Zn dilution. Muon spectroscopy shows the absence of frozen moments, inelastic neutron scattering exhibits a continuum of excitations (mimicking a spinon continuum), and the plateau in 1/T 1 of NMR measurements confirms a fluctuating behavior down to 20 mK.…”

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confidence: 99%

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Gapless chiral spin liquid in a kagome Heisenberg model

et al. 2015

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Motivated by recent experiments on the Heisenberg S = 1/2 quantum spin liquid candidate material kapellasite, we classify all possible chiral (time-reversal symmetry breaking) spin liquids with fermionic spinons on the kagome lattice. We obtain the phase diagram for the physically relevant extended Heisenberg model, comparing the energies of a wide range of microscopic variational wave functions. We propose that, at low temperature, kapellasite exhibits a gapless chiral spin liquid phase with spinon Fermi surfaces. This two-dimensional state inherits many properties of the nearby one-dimensional phase of decoupled antiferromagnetic spin chains, but also shows some remarkable differences. We discuss the spin structure factors and other physical properties.PACS numbers: 75.10. Jm, 75.10.Kt, 75.30.Kz, 75.10.Pq When low dimensionality, geometric frustration, and antiferromagnetism conspire in quantum magnets, completely novel and exotic physics can emerge at low temperature. In such quantum spin liquid (QSL) phases, the picture of classical magnetic moments breaks down, and fractionalized spinon quasiparticles with unusual statistics and long-range entanglement properties become relevant [1]. After intense theoretical research activity on quantum spin liquids in the late 1980's and 1990's due to their intimate relation with high-temperature superconductivity [2], interest in QSL has recently regained momentum because of possible applications in quantum computing [3]. More strikingly, however, enormous experimental progress in synthetization and characterization of actual spin liquid candidate materials has catapulted the field to an unprecedented stage of maturity in this century (see and references therein).A highly interesting, recently synthesized QSL candidate material is the so-called kapellasite [14][15][16][17]: X-ray diffraction on powder samples of this strong Mott insulator indicates geometrically perfect, uncoupled twodimensional kagome layers of spin S = 1/2 Cu ions, despite some on-site Cu/Zn dilution. Muon spectroscopy shows the absence of frozen moments, inelastic neutron scattering exhibits a continuum of excitations (mimicking a spinon continuum), and the plateau in 1/T 1 of NMR measurements confirms a fluctuating behavior down to 20 mK. Experiments on kapellasite therefore provide quite strong evidence in favor of a genuine gapless QSL phase in this material.In contrast to its polymorph herbertsmithite [12, 13] -one of the best studied QSL candidate to date -kapellasite is known to have important exchange interactions between farther-neighbor sites in the kagome plane [18,19]. Recent accurate high-temperature series expansions and their fits to susceptibility and specific heat data revealed ferromagnetic interactions on first and second neighbors, while a dominant antiferromagnetic exchange of J d 16 K is present across the hexagons of the lattice [16,17].These results open up exciting new theoretical prospects, because classical spin models on the kagome lattice with such farther-neighbor inte...

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Gapless chiral spin liquid in a kagome Heisenberg model

et al. 2015

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“…From the fitting, the quadrupole frequency and the asymmetric parameter are determined to be ν Q = 2.25(9) MHz and η = 0.4 (1). Comparable values of ν Q were reported for Zn-kapellasite, for which the local environment around the Cl site is similar to that for Ca-kapellasite [19]. In Zn-kapellasite, however, …”

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Gapless magnetic excitations in the kagome antiferromagnet Ca-kapellasite probed by Cl35 NMR spectroscopy

et al. 2017

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The low-energy magnetic excitations of the spin-1/2 kagome antiferromagnet CaCu 3 (OH) 6 Cl 2 · 0.6H 2 O (Ca-kapellasite) have been investigated by a 35 Cl NMR experiment in fields up to 18.9 T. Recently, Ca-kapellasite was found to be one of the most promising candidates to explore the intrinsic magnetic properties in kagome antiferromagnets, because magnetic defects, which deteriorate the intrinsic magnetic properties, are minimized by choosing Ca ions with a large ionic radius as the counterions. From our nuclear spin-lattice relaxation rate 1/T 1 measurement, we found a power-law temperature dependence below the magnetic ordering temperature T M = 7.2 K, which leads us to suggest that gapless magnetic excitations survive even in the ordered state. This power-law behavior is suppressed in high magnetic fields. We discuss a possible magnetic state that can generate gapless excitations at low fields. DOI: 10.1103/PhysRevB.96.180409 In quantum magnets with 1/2 spins, when the canonical magnetic ordering is disturbed by geometrical frustration and/or low-dimensionality effects, strong quantum fluctuations at low temperatures stabilize exotic spin states. The most apparent quantum fluctuation effect is expected for antiferromagnetically interacting spins on a kagome network, because the corner-sharing triangle network reduces the number of neighboring spins (Z = 4). In these kagome antiferromagnets (KAFMs), macroscopic numbers of spin states are degenerate or pseudodegenerate at very low energy, and therefore the exotic spin states, which never appear in canonical antiferromagnets, can be stabilized by a small energy perturbation, such as magnetic fields. Although interesting, an unperturbed ground state is hard to be picked out from the huge numbers of possible candidates [1]. In fact, theoretical studies have proposed various quantum spin-liquid states with gaps or without gaps in the spin excitation spectrum. A gapped topological Z 2 state was suggested from the density matrix renormalization group theory [2], while a gapless U (1)-Dirac state was suggested from the Gutzwiller projection technique [3] and also from the recently developed tensor-network method [4]. To reveal the intrinsic ground state, which appears in real materials, an experimental search for a perfect KAFM is compulsory. At this time, the most promising candidate material for the perfect KAFM is the mineral herbertsmithite [ZnCu 3 (OH) 6 Cl 2 ] [5], for which many experimental studies have been performed [6][7][8][9][10][11], and a gapped spin-liquid ground state has been suggested from the latest 17 O NMR spectroscopy study for the single crystal [12]. In herbertsmithite, however, the site exchange between magnetic Cu and nonmagnetic Zn creates isolated spins [13], which can deteriorate the proposed intrinsic ground state for a clean system. Searches for the perfect KAFM have been carried out for long time [14][15][16][17].The recently reported candidate for a KAFM is Cakapellasite [CaCu 3 (OH) 6 Cl 2 · 0.6H 2 O], for which an x-ray diff...

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“…Prominent examples for s = 1/2 kagome compounds are herbertsmithite [49][50][51][52][53] and kapellasite [54,55]. Both compounds do not show magnetic order down to very low temperatures [49][50][51][52][53][54][55]. However, the underlying magnetic model is quite different.…”

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The route to magnetic order in the spin-1/2 kagome Heisenberg antiferromagnet: The role of interlayer coupling

Götze¹,

Richter²

2016

EPL

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While the existence of a spin-liquid ground state of the spin-1/2 kagome Heisenberg antiferromagnet (KHAF) is well established, the discussion of the effect of an interlayer coupling (ILC) by controlled theoretical approaches is still lacking. Here we study this problem by using the coupledcluster method to high orders of approximation. We consider a stacked KHAF with a perpendicular ILC J ⊥ , where we study ferro-as well as antiferromagnetic J ⊥ . We find that the spin-liquid ground state (GS) persists until relatively large strengths of the ILC. Only if the strength of the ILC exceeds about 15% of the intralayer coupling the spin-liquid phase gives way for q = 0 magnetic long-range order, where the transition between both phases is continuous and the critical strength of the ILC, |J c ⊥ |, is almost independent of the sign of J ⊥ . Thus, by contrast to the quantum GS selection of the strictly two-dimensional KHAF at large spin s, the ILC leads first to a selection of the q = 0 GS. Only at larger |J ⊥ | the ILC drives a first-order transition to the √ 3 × √ 3 long-range ordered GS. As a result, the stacked spin-1/2 KHAF exhibits a rich GS phase diagram with two continuous and two discontinuous transitions driven by the ILC. Introduction.-The search for exotic quantum spin liquid (QSL) states and fractionalized quasiparticles in frustrated magnets attracts currently much attention both from the theoretical and experimental side. One of the most promising, fascinating, and, at same time, challenging problems is the investigation of the ground state (GS) of the quantum antiferromagnet on the kagome lattice. Over the last 25 years a plethora of theoretical approaches has been applied to understand the GS properties of the spin-1/2 kagome antiferromagnet (KAFM), see, e.g., Refs. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Clearly, the GS of the s = 1/2 Heisenberg KAFM does not exhibit GS magnetic longrange order (LRO). However, there is a long-standing debate on the nature of the quantum GS. Recent largescale numerical studies [6,8,11] provide arguments for a gapped Z 2 topological QSL for spin s = 1/2. However, the gap state is not fully proven, and also a gapless spin liquid is suggested, see, e.g., Refs. [9,12,16].

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Spin dynamics and disorder effects in theS=12kagome Heisenberg spin-liquid phase of kapellasite

Cited by 53 publications

References 57 publications

Gapless chiral spin liquid in a kagome Heisenberg model

Gapless chiral spin liquid in a kagome Heisenberg model

Gapless magnetic excitations in the kagome antiferromagnet Ca-kapellasite probed by Cl35 NMR spectroscopy

The route to magnetic order in the spin-1/2 kagome Heisenberg antiferromagnet: The role of interlayer coupling

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