Oral Session D1 (Friday, February 16)
Chair: Tomas Jungwirth,
Academy of Sciences of the Czech Republic (ASCR)

Keynote Talk
9 : 00 - 9 : 40

Stefan BlügelPeter Grünberg Institute and Institute for Advanced Simulation,
Forschungszentrum Jülich and JARA

From the Fermi surface to topologicalmagnetization textures
Topological magnetization textures such as skyrmions are solutions of nonlinear field equations.
They are typically metastable and in the past mostly stabilized by the Dzyaloshinskii-Moriya
interaction (DMI), recently increasingly also by frustrated exchange, and sometimes withhigher-order exchange interactions. In this context, centrosymmetric intermetallic rare-earth
compounds (e.g. Gd2PdSi3 GdRu2Si2, EuAl4) constitute a very flexible play-ground for therealization of topological magnetization textures (e.g. skyrmion lattices) relying on the RudermanKittel-Kasuya-Yosida (RKKY) interaction between the localized 4f-moments [1-3] which directlydepend on the details of the Fermi surface. We perform a systematic first-principles analysis in theframework of the DFT+U and relate the Fermi-surface and electronic properties to magnetic
interaction parameters of spin models. Since the exchange interaction is much larger than theDMI, the skrymions are so small that transport properties beyond the adiabatic approximation areconsidered [4]. We employ atomistic spin-dynamics simulations and identify the magnetic phasesthat are stabilized in the presence of an external magnetic field. Our analysis aims at drawing adirect connection between the topology of the electronic band structure and the spin structures inreal space.
We acknowledge funding from ERC grant 856538 (project "3D MAGIC”), the DeutscheForschungsgemeinschaft (DFG) through SPP-2137 and SFB-1238 (project C1).
References[1] H. Kontani et al., Giant orbital Hall eﬀect in transition metals: Origin of large spin and anomalous Halleﬀects. Phys. Rev. Lett. 102, 016601 (2009).
[2] D. Go and D. Jo, C. Kim, and H.-W. Lee, Intrinsic spin and orbital Hall eﬀects from orbital texture.
Phys. Rev. Lett. 121, 086602 (2018).
[3] D. Go and H.-W. Lee, Orbital torque: Torque generation by orbital current injection. Phys. Rev. Research
2, 013177 (2020).
[4] D. Lee et al., Orbital torque in magnetic bilayers. Nat. Commun. 12, 6710 (2021).
[5] S. Lee et al., Eﬃcient conversion of orbital Hall current to spin current for spin-orbit torque switching.
Commun. Phys. 4, 234 (2022).
[6] S. Han et al., Theory of orbital pumping. arXiv:2311.00362 (2023).

Oral Session D1 (Friday, February 16)
Chair: Tomas Jungwirth,
Academy of Sciences of the Czech Republic (ASCR)

Contributed Oral
9 : 40 - 10 : 00

Observation of cluster magnetic octupole domains in theantiferromagnetic Weyl semimetal Mn3Sn nanowireusing an atomic force microscope
H. Isshiki1, 2, N. Budai1, A. Kobayashi1, R. Uesegi1, Z. Zhu1, T. Higo1, 2, 3,S. Nakatsuji1, 2, 3, 5 and Y. Otani1, 2, 4, 5
1. Institute for Solid State Physics, The University of Tokyo, Japan
2. CREST, Japan Science and Technology Agency (JST), Japan.
3. Department of Physics, The University of Tokyo, Japan
4. Trans-scale Quantum Science Institute, The University of Tokyo, Japan.
5. Center for Emergent Matter Science RIKEN, JapanThe antiferromagnetic Weyl semimetals such as Mn3Sn [1] have recently attract wide attention due to theiranomalous transverse transport properties despite having barely any net magnetization. In this study, we visualized
the cluster magnetic octupole domains in a (0001)textured Mn3Sn nanowire using an atomic force microscope.
Our technique involves establishing a tip-sample contact, inducing a localized vertical temperature gradient, andmeasuring the thermoelectric voltages due to the anomalous Nernst eﬀect at the wire's ends [2,3] as illustrated inFigs. 1(a). We show a topographic image of the Mn3Sn wire in Fig. 1(b). After the application of a magnetic field 2
T along the y-direction, we obtained the corresponding anomalous Nernst voltage map at 0 T as shown in Fig.
1(c). This represents the distribution of the y-component of the cluster magnetic octupole moments in a remanentstate. The inhomogeneous voltage signal reflects the presence of the grains with tilted Kagome planes about thex-axis. Not like the magnetic imaging by the stray field measurement, our approach directly maps the distributionof the cluster magnetic octupole moments in Mn3Sn. Our work provides a solid methodology to investigate themagnetic structures of the antiferromagnetic Weyl semimetals.
References[1] S. Nakatsuji et al., Nature 527, (2015)[2] N. Budai et al., Appl. Phys. Lett. 122, 102401 (2023)[3] H. Isshiki et al., Front. Phys. 11 (2023)

Oral Session D1 (Friday, February 16)
Chair: Tomas Jungwirth,
Academy of Sciences of the Czech Republic (ASCR)

Contributed Oral
10 : 00 - 10 : 20

Topological magneto-optical eﬀect from skyrmion lattice
Y. Okamura1, Y. D. Kato1, M. Hirschberger1,2, Y. Tokura1,2,3, and Y. Takahashi1,21. Department of Applied Physics and Quantum Phase Electronics Center, University of Tokyo, Japan
2. RIKEN Center for Emergent Matter Science, Japan
3. Tokyo College, University of Tokyo, Japan

Magnetic skyrmions are nanometric whirlpools of spins, where the directions of the constituent spins wrap the unit
sphere [1], attracting enormous attention as potential information carriers in next-generation memory/logicdevices. Due to their non-coplanar spin arrangement, the resultant scalar spin chirality gives rise to the fictious
magnetic field (emergent magnetic field) acting on the conduction electrons, which leads to unique transportphenomena such as the topological Hall eﬀect. However, other emergent electromagnetic phenomena, forexample, skyrmion-driven optical response have yet to be reported.
In this presentation, we show the observation of the topological magneto-optical Kerr eﬀect in the centrosymmetricmaterial Gd2PdSi3 [2,3]. Magneto-optical eﬀects are polarization rotation phenomena under breaking oftime-reversal symmetry, whose magnitude is usually proportional to the magnetization. In Gd2PdSi3, the Kerr eﬀect
in the mid-infrared region exhibits a significant enhancement in the skyrmion lattice phase, demonstrating theexistence of a topological Kerr signal (Fig. 1). The topological Kerr eﬀect is observed up to the sub-eV region, whichindicates that the formation of the skyrmion lattice causes a reconstruction of the electronic band structure. Ourfindings establish novel emergent optical phenomena, which enables noncontact, fast and eﬃcient readout ofskyrmions.
References[1] C. Back et al., J. Phys. D: Appl. Phys. 53, 363001 (2020).
[2] T. Kurumaji et al., Science 365, 914 (2019).
[3] Y. D. Kato, Y. Okamura et al., Nat. Commun. 14, 5416 (2023).

Oral Session D1 (Friday, February 16)
Chair: Tomas Jungwirth,
Academy of Sciences of the Czech Republic (ASCR)

Contributed Oral
10 : 20 - 10 : 40

First principles calculation of topological Hall
conductance in the skyrmion lattice
Hsiao-Yi Chen1, Takuya Nomoto2, and Ryotaro Arita1, 2
1. RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
2. Research Center for Advanced Science and Technology, University of Tokyo, Komaba Meguro-ku, Tokyo 153-8904, Japan

Noncoplanar topologically protected spinor excitations, such as Skyrmions, have attracted significant attention in
the field of spintronics, due to their stability and low energy costs in manipulation, as a prospective candidate for
information storage. While experimentalists have made strides in advancing our understanding of Skyrmions
through measurements of the unique topological Hall conductance (THC) and real-space imaging using theLorentz TEM technique, theoretical investigations have predominantly relied on empirical modeling, lacking acomprehensive predictive tool.
In response to this gap, we developed a first-principle approach for computing the transport properties ofSkyrmionic systems. In this presentation, we introduce our method for calculating the THC in the Skyrmion
lattice, employing density functional theory. Our approach incorporates the magnetic field induced bynoncoplanar spinors into the current scheme that utilizes the Kubo formula within the wannier tight-binding
model [1]. To validate our formalism, we apply it to investigate the THC of the Skyrmion lattice phase in theGd2PdSi3 crystal and achieve a remarkable agreement with experimental measurements [2]. Additionally, weanalyze the spin on the Fermi surface, obtaining polarization consistent with those derived from aphenomenological model, thereby confirming the reliability of the theoretical discussion adopted in the literature.
References[1] X. Wang, J. R. Yates, I. Souza, and D. Vanderbilt, Ab initio calculation of the anomalous hall conductivity by wannierinterpolation, Phys. Rev. B 74, 195118 (2006).
[2] T. Kurumaji, T. Nakajima, M. Hirschberger, A. Kikkawa, Y. Yamasaki, H. Sagayama, H. Nakao, Y. Taguchi, T.-h. Arima,and Y. Tokura, Skyrmion lattice with a giant topological hall eﬀect in a frustrated triangular-lattice magnet, Science 365, 914(2019).