Weyl magnons in breathing pyrochlore antiferromagnets

Li, Fei Ye; Li, Yao Dong; Kim, Yong Baek; Balents, Leon; Yu, Yue; Chen, Gang

doi:10.1038/ncomms12691

Cited by 226 publications

(191 citation statements)

References 34 publications

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“…These results have established that a TRS-broken chiral spin texture can lead to nontrivial topological spin excitations in frustrated magnets as opposed to previous studies in which the DMI is the primary source of topological spin excitations [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]44].…”

Section: Arxiv:160804561v12 [Cond-matstr-el] 16 Jan 2017mentioning

confidence: 69%

Topological thermal Hall effect in frustrated kagome antiferromagnets

Owerre

2017

Phys. Rev. B

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In frustrated magnets the Dzyaloshinsky-Moriya interaction (DMI) arising from spin-orbit coupling (SOC) can induce a magnetic long-range order. Here, we report a theoretical prediction of thermal Hall effect in frustrated kagomé magnets such as KCr3(OH)6(SO4)2 and KFe3(OH)6(SO4)2. The thermal Hall effects in these materials are induced by scalar spin chirality as opposed to DMI in previous studies. The scalar spin chirality originates from magnetic-field-induced chiral spin configuration due to non-coplanar spin textures, but in general it can be spontaneously developed as a macroscopic order parameter in chiral quantum spin liquids. Therefore, we infer that there is a possibility of thermal Hall effect in frustrated kagomé magnets such as herbertsmithite ZnCu3(OH)6Cl2 and the chromium compound Ca10Cr7O28, although they also show evidence of magnetic long-range order in the presence of applied magnetic field or pressure.Introduction-. Topological phases of matter are an active research field in condensed matter physics, mostly dominated by electronic systems. Quite recently the concepts of topological matter have been extended to nonelectronic bosonic systems such as quantized spin waves (magnons) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and quantized lattice vibrations (phonons) [18][19][20][21][22][23]. In the former, spin-orbit coupling manifests in the form of Dzyaloshinsky-Moriya interaction [24,25] and it leads to topological spin excitations and chiral edge modes in collinear ferromagnets [5,6]. The quantized spin waves or magnons are charge-neutral quasiparticles and they do not experience a Lorentz force as in charge particles. However, a temperature gradient can induce a heat current and the DMI-induced Berry curvature acts as an effective magnetic field in momentum space. This leads to a thermal version of the Hall effect characterized by a temperature dependent thermal Hall conductivity [1,3]. Thermal Hall effect is now an emerging active research area for probing the topological nature of magnetic spin excitations in quantum magnets. The thermal Hall effect of spin waves has been realized experimentally in a number of pyrochlore ferromagnets [2,4]. Recently, DMI-induced topological magnon bands and thermal Hall effect have been observed in collinear kagomé ferromagnet Cu(1-3, bdc) [8,9].In frustrated kagomé magnets, however, there is no magnetic long-range order (LRO) down to the lowest accessible temperatures. The classical ground states have an extensive degeneracy and they are considered as candidates for quantum spin liquid (QSL) [26,27]. The ground state of spin-1/2 Heisenberg model on the kagomé lattice is believed to be a U(1)-Dirac spin liquid [28]. In physical realistic materials, however, there are other interactions and perturbations that tend to alleviate QSL ground states and lead to LRO. Recent experimental syntheses of kagomé antiferromagnetic materials have shown that the effects of SOC or DMI are not negligible in frustrated magnets. The DMI is an intrinsic pertur...

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Section: Arxiv:160804561v12 [Cond-matstr-el] 16 Jan 2017mentioning

confidence: 69%

Topological thermal Hall effect in frustrated kagome antiferromagnets

Owerre

2017

Phys. Rev. B

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“…Of particular interest are magnetic excitations with nontrivial band structure topology, since they exhibit protected magnon or triplon edges states. This was recently studied for triplons in the ordered phase of the Shastry-Sutherland model [9,18,19] and for magnons in an ordered pyrochlore antiferromagnet [20] as well as in an ordered honeycomb ferromagnet [21]. However, the development of a comprehensive topological band theory for magnetic excitations is still in its infancy.…”

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confidence: 99%

Topological quantum paramagnet in a quantum spin ladder

Joshi

Schnyder

2017

Phys. Rev. B

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It has recently been found that bosonic excitations of ordered media, such as phonons or spinons, can exhibit topologically nontrivial band structures. Of particular interest are magnon and triplon excitations in quantum magnets, as they can easily be manipulated by an applied field. Here we study triplon excitations in an S=1/2 quantum spin ladder and show that they exhibit nontrivial topology, even in the quantum-disordered paramagnetic phase. Our analysis reveals that the paramagnetic phase actually consists of two separate regions with topologically distinct triplon excitations. We demonstrate that the topological transition between these two regions can be tuned by an external magnetic field. The winding number that characterizes the topology of the triplons is derived and evaluated. By the bulk-boundary correspondence, we find that the non-zero winding number implies the presence of localized triplon end states. Experimental signatures and possible physical realizations of the topological paramagnetic phase are discussed.The last decade has witnessed tremendous progress in understanding and classifying topological band structures of fermions [1][2][3][4]. Soon after the discovery of fermionic topological insulators [5,6], it was recognized that bosonic excitations of ordered media can as well exhibit topologically nontrivial bands [7][8][9][10][11]. Such bosonic topological bands have been observed not long ago for photons in dielectric superlattices [12]. Theoretical proposals of topological states in polaritonic systems have been made [13][14][15], some of which have been observed experimentally [16]. Besides these examples, bosonic band structures are also realized by elementary excitations of quantum spin systems, e.g., by magnons in (anti)ferromagnets or by triplons in dimerized quantum magnets.The study of these collective spin excitations is enjoying growing interest, due to potential applications for magnonic devices and spintronics [17]. Because magnetic excitations are charge neutral, they are weakly interacting, and therefore exhibit good coherence and support nearly dissipationless spin transport. Moreover, the properties of spin excitations are easily tunable by magnetic fields of moderate strength, as the magnetic interaction scale is in most cases relatively small. Of particular interest are magnetic excitations with nontrivial band structure topology, since they exhibit protected magnon or triplon edges states. This was recently studied for triplons in the ordered phase of the Shastry-Sutherland model [9,18,19] and for magnons in an ordered pyrochlore antiferromagnet [20] as well as in an ordered honeycomb ferromagnet [21]. However, the development of a comprehensive topological band theory for magnetic excitations is still in its infancy. Specifically, it has remained unclear whether topological spin excitations can exist also in quantum disordered paramagnets.In this paper, we address this question by considering, as a prototypical example, the paramagnetic phase of an S=1/2 quantum spin ...

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“…Based on these studies, Ezawa [23] proposed a wide class of 3D honeycomb lattices constructed by two building blocks. These 3D honeycomb lattices can display all loop-nodal semimetals which can be gapped to be strong topological insulators by SOI or point nodal semimetals by SOI together with an antiferromagnetic order.Recently, the topology of band has been extended to magnetic excitations as well [24][25][26][27][28][29][30][31][32][33], including magnon Chern insulators [24][25][26][27][28][29], Weyl magnons [30,31], magnon nodal-line semimetals [32] and Dirac magnons [33]. Interestingly, the magnon excitations on a 2D honeycomb lattice with a ferromagnetic ground state have two Dirac points in the first Brillouin zone [28], and a proper DM interaction can gap the system into a magnon Chern insulator, reminiscent of the role of SOI in the graphene [1,2].…”

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confidence: 99%

Weyl and Nodal Ring Magnons in Three-Dimensional Honeycomb Lattices

2017

Chinese Phys. Lett.

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We study the topological properties of magnon excitations in a wide class of three dimensional (3D) honeycomb lattices with ferromagnetic ground states. It is found that they host nodal ring magnon excitations. These rings locate on the same plane in the momentum space. The rings can be gapped by Dzyaloshinskii-Moriya (DM) interactions to form two Weyl points with opposite charges. We explicitly discuss these physics in the simplest 3D honeycomb lattice, the hyperhoneycomb lattice and show drumhead and arc surface states in the nodal ring and Weyl phases, respectively, due to the bulk-boundary correspondence. PACS numbers: 75.30.Ds, 75.50.Dd, 75.70.Rf, 75.90.+w Introduction. Two dimensional (2D) honeycomb lattice can be realized in graphene, silicene and many other related materials. Its two Dirac points in the first Brillouin zone make it one of the most fascinating research field in condensed matter physics. When the spin-orbit interaction (SOI) is large, the band structure of the system is topologically nontrivial and becomes a topological insulator [1,2].Naturally, there are also 3D honeycomb lattices [3][4][5][6][7][8][9][10][11][12][13][14], and their exotic properties have been explored, such as nodal line semimetal in body-centered orthorhombic C 16 [3], loop-nodal semimetal [7,9] and topological insulator [7] in the hyperhoneycomb lattice, nodal ring [14,15] and Weyl [14] spinons of interacting spin systems in the hyperhoneycomb and stripyhoneycomb lattices, and loop Fermi surface in other similar systems [16][17][18][19][20][21][22]. Based on these studies, Ezawa [23] proposed a wide class of 3D honeycomb lattices constructed by two building blocks. These 3D honeycomb lattices can display all loop-nodal semimetals which can be gapped to be strong topological insulators by SOI or point nodal semimetals by SOI together with an antiferromagnetic order.Recently, the topology of band has been extended to magnetic excitations as well [24][25][26][27][28][29][30][31][32][33], including magnon Chern insulators [24][25][26][27][28][29], Weyl magnons [30,31], magnon nodal-line semimetals [32] and Dirac magnons [33]. Interestingly, the magnon excitations on a 2D honeycomb lattice with a ferromagnetic ground state have two Dirac points in the first Brillouin zone [28], and a proper DM interaction can gap the system into a magnon Chern insulator, reminiscent of the role of SOI in the graphene [1,2]. Therefore, we can ask a natural question whether there exist magnon excitations on 3D honeycomb lattices with special properties such as nodal lines and nodal points, similar to those in electronic systems [23].In this paper, we provide an affirmative answer to the above question. Use the linear spin-wave approximation, we study the magnon excitations on the wide class of 3D honeycomb lattices proposed in [23]. We consider a Heisenberg model with isotropic nearest neighbor ferromagnetic exchange interactions. We find that all the 3D honeycomb lattices host magnon nodal rings located in the k z = 0 plane. Furthermore,...

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Weyl magnons in breathing pyrochlore antiferromagnets

Cited by 226 publications

References 34 publications

Topological thermal Hall effect in frustrated kagome antiferromagnets

Topological thermal Hall effect in frustrated kagome antiferromagnets

Topological quantum paramagnet in a quantum spin ladder

Weyl and Nodal Ring Magnons in Three-Dimensional Honeycomb Lattices

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