For magnons, the Dzyaloshinskii-Moriya interaction accounts for spin-orbit interaction and causes a nontrivial topology that allows for topological magnon insulators. In this theoretical investigation we present the bulkboundary correspondence for magnonic kagome lattices by studying the edge magnons calculated by a Green function renormalization technique. Our analysis explains the sign of the transverse thermal conductivity of the magnon Hall effect in terms of topological edge modes and their propagation direction. The hybridization of topologically trivial with nontrivial edge modes enlarges the period in reciprocal space of the latter, which is explained by the topology of the involved modes.

A magnetic bimeron is a pair of two merons and can be understood as the in-plane magnetized version of a skyrmion. Here we theoretically predict the existence of single magnetic bimerons as well as bimeron crystals, and compare the emergent electrodynamics of bimerons with their skyrmion analogues. We show that bimeron crystals can be stabilized in frustrated magnets and analyze what crystal structure can stabilize bimerons or bimeron crystals via the Dzyaloshinskii-Moriya interaction. We point out that bimeron crystals, in contrast to skyrmion crystals, allow for the detection of a pure topological Hall effect. By means of micromagnetic simulations, we show that bimerons can be used as bits of information in in-plane magnetized racetrack devices, where they allow for current-driven motion for torque orientations that leave skyrmions in out-of-plane magnets stationary.Over the last years magnetic skyrmions [ Fig. 1(a) top] [1-6] have attracted immense research interest, as these small spin textures m(r) possess strong stability, characterized by a topological charge N Sk = ±1. Skyrmions offer a topological contribution to the Hall effect [7][8][9][10][11][12][13][14][15][16][17][18], commonly measured in skyrmion crystals, and can be stabilized as individual quasiparticles in collinear ferromagnets. They can be driven by currents in thin films [6,[19][20][21][22][23][24][25][26] allowing for spintronics applicability. The stabilizing interaction in most systems is the Dzyaloshinskii-Moriya interaction (DMI) [27,28], while theoretical simulations also point to other stabilizing mechanisms, e. g. frustrated exchange interactions [29,30]. Textures with a half-integer topological charge, like merons and antimerons (or vortices and antivortices), have also been subject of intense research [31][32][33].Magnetic bimerons [34][35][36][37] [Fig.1(a) bottom] are the combination of two merons [red and blue] and can be understood as in-plane magnetized versions of magnetic skyrmions [38]. Instead of the out-of-plane component of the magnetization it is an in-plane component which is radial symmetric about the quasiparticle's center; being aligned with the saturation magnetization of the ferromagnet at the outer region of the bimeron and pointing into the opposite direction in the center. Recently, Kharkov et al. showed that isolated bimerons can be stabilized in an easy-plane magnet by frustrated exchange interactions [34]. In DMI dominated systems (as is the case for all experimentally known skyrmion-host materials) bimerons have only been shown to exist as unstable transition states [35,36].In this Rapid Communication, we show that bimerons in frustrated magnets can also be stabilized in an array, the bimeron crystal. Furthermore, we propose a structural configuration that allows for DMI stabilizing isolated bimerons and bimeron crystals. We compare fundamental properties of skyrmions and bimerons and find that both show the same topological Hall effect, whereas the bimeron allows for a pure detection, that is without supe...

Ferromagnetic insulators with Dzyaloshinskii-Moriya interaction show the magnon Hall effect, i.e., a transverse heat current upon application of a temperature gradient. In this theoretical investigation we establish a close connection of the magnon Hall effect in two-dimensional kagome lattices with the topology of their magnon dispersion relation. From the topological phase diagram we predict systems which show a change of sign in the heat current in dependence on temperature. Furthermore, we derive the high-temperature limit of the thermal Hall conductivity; this quantity provides a figure of merit for the maximum strength of the magnon Hall effect. Eventually, we compare the temperature and field dependence of the magnon Hall conductivity of the three-dimensional pyrochlore Lu 2 V 2 O 7 with experimental results.

We have used s-and p-polarized synchrotron radiation to image the electronic structure of epitaxial graphene near the K-point by angular resolved photoemission spectroscopy (ARPES). Part of the experimental Fermi surface is suppressed due to the interference of photoelectrons emitted from the two equivalent carbon atoms per unit cell of graphene's honeycomb lattice. Here we show that by rotating the polarization vector, we are able to illuminate this 'dark corridor' indicating that the present theoretical understanding is oversimplified. Our measurements are supported by first-principles photoemission calculations, which reveal that the observed effect persists in the low photon energy regime.Graphene, a single layer of sp 2 -bonded carbon atoms, is one of the paradigm two-dimensional (2D) electron systems existing today. It is renowned for its high crystalline quality, its extremely high carrier mobility [1][2][3] as well as its peculiar charge carriers that behave like massless Dirac particles [2,[4][5][6][7][8] due to its honeycomb lattice consisting of two equivalent triangular sublattices A and B (see Fig. 1a). This leads to the description of graphene's charge carriers in terms of spinor . Panel (c) shows a sketch of the experimental setup. ky corresponds to a rotation of the sample around φ. kx is the direction perpendicular to the paper plane, it corresponds to the dispersion direction in the 2D detector. For s(p)-polarized light the electric field vector lies perpendicular to the plane of incidence (in the plane of incidence) spanned by the sample normal and the direction of incidence of the light.wavefunctions in analogy to the Dirac equation for massless particles, where the 'spin' index indicates the sublattice rather than the real electron spin, hence the term 'pseudospin ' [6]. This pseudospin is responsible for graphene's many intriguing electronic properties. First of all, the difference in pseudospin of the two cosine-shaped bands originating from the two sublattices allows them to cross at the K-point of the 2D Brillouin zone (see Fig. 1b) where they form the conical band structure [9,10]. Second, due to the pseudospin the charge carriers accumulate a Berry phase of π on closed loop paths resulting in the absence of backscattering. This has been observed in both magnetotransport [11][12][13][14] as well as scanning tunneling spectroscopy experiments [15]. Furthermore, the pseudospin is responsible for the peculiar half-integer quantum Hall effect observed in graphene [4,5,16]. In addition, the conservation of the pseudospin upon passing a potential barrier is expected to result in perfect transparency of the barrier for graphene's charge carriers (Klein tunneling) [17]. The pseudospin concept has spawned ideas for different 'pseudospintronic' device proposals, like e.g. the pseudospin valve [18].The effect of the pseudospin is also observed in angleresolved photoemission spectroscopy (ARPES) experiments. Here, it is rather unwanted because it suppresses the photoemission intensity on part of th...

The dispersion relations of magnons in ferromagnetic pyrochlores with Dzyaloshinskii-Moriya interaction is shown to possess Weyl points, i. e., pairs of topological nontrivial crossings of two magnon branches with opposite topological charge. As a consequence of their topological nature, their projections onto a surface are connected by magnon arcs, thereby resembling closely Fermi arcs of electronic Weyl semimetals. On top of this, the positions of the Weyl points in reciprocal space can be tuned widely by an external magnetic field: rotated within the surface plane, the Weyl points and magnon arcs are rotated as well; tilting the magnetic field out-ofplane shifts the Weyl points toward the center Γ of the surface Brillouin zone. The theory is valid for the class of ferromagnetic pyrochlores, i. e., three-dimensional extensions of topological magnon insulators on kagome lattices. In this Letter, we focus on the (111) surface, identify candidates of established ferromagnetic pyrochlores which apply to the considered spin model, and suggest experiments for the detection of the topological features.