Topological triplon modes and bound states in a Shastry–Sutherland magnet

McClarty, Paul A.; Krüger, Frank; Guidi, T.; Parker, Stewart F.; Refson, Keith; Parker, A. W.; Prabhakaran, D.; Coldea, R.

doi:10.1038/nphys4117

Cited by 110 publications

(114 citation statements)

References 34 publications

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“…In this paper, we propose that magnonic systems may be a nearly ideal platform to realize non-Hermitian topological states. Topological magnon states have been widely discussed in the Hermitian context [37][38][39][40][41][42][43][44][45][46][47]. One of the peculiarities of topological magnons compared to their electronic cousins is that they appear as excited states and therefore they are sub- ject to the non-universal effects of interactions [42,44,47].…”

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confidence: 99%

Non-Hermitian topology of spontaneous magnon decay

McClarty

Rau

2019

Phys. Rev. B

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Spontaneous magnon decay is a generic feature of the magnetic excitations of anisotropic magnets and isotropic magnets with non-collinear order. In this paper, we argue that the effect of interactions on one-magnon states can, under many circumstances, be treated in terms of an effective, energy independent, non-Hermitian Hamiltonian for the magnons. In the vicinity of Dirac or Weyl touching points, we show that the spectral function has a characteristic anisotropy arising from topologically protected exceptional points or lines in the non-Hermitian spectrum. Such features can, in principle, be detected using inelastic neutron scattering or other spectroscopic probes. We illustrate this physics through a concrete example: a honeycomb ferromagnet with Dzyaloshinskii-Moriya exchange. We perform interacting spin wave calculations of the structure factor and spectral function of this model, showing good agreement with results from a simple effective non-Hermitian model for the splitting of the Dirac point. Finally, we argue that the zoo of known topological protected magnon band structures may serve as a nearly ideal platform for realizing and exploring non-Hermitian physics in solidstate systems.arXiv:1904.02160v1 [cond-mat.str-el]

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confidence: 99%

Non-Hermitian topology of spontaneous magnon decay

McClarty

Rau

2019

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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“…4D INS is applied quite frequently to inorganic magnetic compounds or metals, where mostly antiferromagnetic (AFM), extended systems are studied , . Impressively complete plots of the magnon dispersion branches in ordered systems can be recorded relatively quickly , , .…”

Section: Introductionmentioning

confidence: 99%

“…Impressively complete plots of the magnon dispersion branches in ordered systems can be recorded relatively quickly , , . The technique is also ideally suited for studying the magnetic correlations in frustrated, disordered systems, where features are typically broad both in energy E and Q space, and are thus difficult if not impossible to identify from measurements at few points or in a limited ( E , Q ) range , , , . Even localized modes, resembling excitations in spin clusters, such as antiferromagnetic fluctuations of hexagons in the cubic spinel ZnCr 2 O 4 were detected …”

Section: Introductionmentioning

confidence: 99%

Inelastic Neutron Scattering Intensities of Ferromagnetic Cluster Spin Waves

Prša

Waldmann

2019

Eur J Inorg Chem

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Inelastic neutron scattering (INS) is the key method for studying magnetic spectra. For ferromagnetic molecular nanomagnets the ferromagnetic cluster spin wave theory (FCSWT) exactly describes the low‐energy excitations from the ferromagnetic ground state. We provide a procedure starting from these molecular spin wave modes and ending with the experimentally observable INS spectra. The formulas for powder and single‐crystal spectra of isotropic and anisotropic ferromagnetic molecules are given. The INS interference pattern can be written in terms of “basis functions” fixed by the molecular geometry. We argue that this decomposition explicates the INS data when the spin wave modes are known and, vice versa, suggests a method to directly determine the quantum wavefunctions of the spin wave excitations based on the INS interference pattern. The calculation of INS observables is exemplified on three molecules: the Mn7 disc, the Mn10 supertetrahedron, and the Mn6 single molecule magnet.

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Topological triplon modes and bound states in a Shastry–Sutherland magnet

Cited by 110 publications

References 34 publications

Non-Hermitian topology of spontaneous magnon decay

Non-Hermitian topology of spontaneous magnon decay

Topological quantum paramagnet in a quantum spin ladder

Inelastic Neutron Scattering Intensities of Ferromagnetic Cluster Spin Waves

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