Local density-of-states imprint of RKKY-stabilized skyrmion crystals visualized using scanning tunneling microscopy

Christopher Butler^1*, Katsuki Nihongi¹, Nguyen Duy Khanh², Haruto Yoshimochi², Rina Takagi^2,3,4, Tetsuo Hanaguri¹, Shinichiro Seki^2,3,4

¹CEMS, RIKEN, Wako, Japan
²Dept. of Applied Physics, University of Tokyo, Tokyo, Japan
³Inst. of Engineering Innovation, University of Tokyo, Tokyo, Japan
⁴PRESTO, Japan Science and Technology Agency (JST)), Kawaguchi, Japan

* Presenter:Christopher Butler, email:christopher.butler@riken.jp

Skyrmions are topologically stable swirling spin structures that have intriguing physical properties as well as potential application in high-density magnetic information storage. It is well-known that skyrmions can be stabilized by the Dzyaloshinskii-Moriya interaction in materials that lack inversion symmetry. However, crystals of nanometer-scale skyrmions have also been observed in inversion-symmetric materials, and here the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction is thought to provide the main stabilizing mechanism. The RKKY interaction is mediated by itinerant electrons near the Fermi level, which are accessible to investigation using a scanning tunneling microscope (STM). Here we use low-temperature STM under varying magnetic field to explore the rich magnetic phase diagram of GdRu₂Ge₂, which includes two skyrmion crystal phases. We see intricate textures in the electronic local density-of-states (LDOS) images corresponding to different magnetic phases. Despite the complexity of the material system, we discover that a simple atomistic rule can be used to generate good approximations to these electronic LDOS textures given knowledge of the underlying spin textures. These observations provide a vantage point to understand the role that itinerant electrons can play in stabilizing topological magnetism, and from which to explore interesting nano-scale phenomena, such as domain walls, hosted within the skyrmion crystals themselves.

Keywords: Itinerant magnetism, RKKY interaction, Skyrmions, Scanning tunneling microscopy