Topological Quantum Matter Research Unit

Principal Investigator

PI Name Max Hirschberger
Degree Ph.D.
Title Unit Leader
Brief Resume
2011Dipl. Phys., Department of Physics, Technical University of Munich, Munich, Germany
2017Ph.D., Department of Physics, Princeton University, Princeton, NJ, USA
2017Postdoctoral Researcher, RIKEN Center for Emergent Matter Science (CEMS)
2018Alexander von Humboldt / JSPS Research Fellow and Visiting Researcher at RIKEN CEMS
2019Project Lecturer, Quantum-Phase Electronics Center, School of Engineering, The University of Tokyo (-present)
2019Unit Leader, Topological Quantum Matter Research Unit, RIKEN CEMS (-present)

 

Outline

We are focused on studying the interplay between magnetic order, in particular non-coplanar spin arrangements such as magnetic skyrmions, and the electronic band structure in solids. A particular emphasis will be put on compounds with the potential to be grown in thin-film form and realizing new types of protected surface states in correlated materials. Methods include materials search guided by standard density functional theory calculations, crystal synthesis using a variety of solid state techniques, and ultra-high resolution transport measurements. We also collaborate closely and regularly with other researchers at RIKEN and beyond to resolve the magnetic structure of new materials using quantum beam scattering experiments and real-space imaging. An important addition to our toolbox is the investigation of physical properties in very high magnetic fields up 45 Tesla (static) or 100 Tesla (transient); for this purpose, we make use of facilities with user programs in Japan, the United States, and Europe.

Research Fields

Physics, Materials Sciences

Keywords

Strongly Correlated electron system
Magnetism
Skyrmion
Spin-orbit interaction
Emergent electromagnetism
Topological materials
Frustrated quantum magnets
Berry phase physics

Results

Skyrmions in a centrosymmetric breathing Kagome magnet

Non-coplanar magnetic order in solids gives rise to an emergent magnetic field, which is known to strongly affect the motion of charge carriers. The magnitude of the emergent magnetic field is enhanced when pushing non-coplanar spin textures to shorter and shorter length scales λ. We have recently explored the limit of ultra-short range spin texture formation (λ~2-3 nanometers) in intermetallic magnets, where we found giant topological Hall and Nernst effects from non-coplanar skyrmion spin vortices. Hexagonal Gd2PdSi3 and Gd3Ru4Al12 are centrosymmetric alloys which defy an important paradigm: typically, it is thought that Dzyaloshinskii-Moriya interactions arising exclusively in non-centrosymmetric material platforms are the key to skyrmion formation. Instead, competing interactions due to the high symmetry of the (hexagonal) lattice combine with Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions between Gd3+ rare earth moments to create a curious non-coplanar ordering on very short length scales. For example, the existence of the skyrmion lattice in Gd3Ru4Al12 was confirmed by quantum beam (neutron & x-ray) scattering experiments as well as real-space imaging using Lorentz transmission electron microscopy (L-TEM), as shown in the figure. Future directions for skyrmions on centrosymmetric lattices are the exploration of new types of domains of left- and right-handed helicity, the coupling of the symmetry-breaking magnetic order to light, and the search for new types of magnetic vortex lattices, such as antiskyrmions or antiferromagnetically stacked skyrmions, due to the high level of spin-orientational degeneracy on the lattice. These exotic forms of magnetic order may be within reach in centrosymmetric magnets due to the flat energy landscape with many nearly degenerate magnetic states.

Skyrmion formation in the centrosymmetric hexagonal metal Gd3Ru4Al12. (a) The crystal structure hosts closely correlated spin-trimers of Gd3+ moments, which are connected by weaker next-nearest neighbor interactions. The rare earth sites in each plane form a distorted (‘breathing’) Kagome network. (b) Illustration of a two-dimensional cut of the skyrmion spin vortex, with each cone representing an individual magnetic moment on a Gd-site of the lattice. (c) Magnetic phase diagram for field aligned along the c-axis, where many magnetic phases are observed due to competing interactions. (d) Only in the skyrmion lattice phase (labeled ‘SkL’) we found a large topological Hall signal, marked by grey shaded areas. (e) Real space image of a thin plate of Gd3Ru4Al12 in phase SkL, where both the atomic lattice and the magnetic texture leave their fingerprints in the data. (f) Fourier transform of the data in panel (e), where reflections due to the atomic lattice and skyrmion spin textures are marked by red and yellow circles, respectively. Inset in (e) shows filtered data after removing intensity originating from the atomic lattice.

Members

Max Hirschberger

Unit Leader maximilian.hirschberger[at]riken.jp R

お問い合わせ

2-1 Hirosawa, Wako, Saitama
Frontier Research Building #208 351-0198 Japan

E-mail:
maximilian.hirschberger[at]riken.jp

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