Ultrastrong to nearly deep-strong magnon-magnon coupling with a high degree of freedom in synthetic antiferromagnets

Yuqiang Wang; Yu Zhang; Chaozhong Li; Jinwu Wei; Bin He; Hongjun Xu; Jihao Xia; Xuming Luo; Jiahui Li; Jing Dong; Wenqing He; Zhengren Yan; Wenlong Yang; Fusheng Ma; Guozhi Chai; Peng Yan; Caihua Wan; Xiufeng Han; Guoqiang Yu

doi:10.1038/s41467-024-46474-7

Ultrastrong to nearly deep-strong magnon-magnon coupling with a high degree of freedom in synthetic antiferromagnets

Nat Commun. 2024 Mar 7;15(1):2077. doi: 10.1038/s41467-024-46474-7.

Authors

Yuqiang Wang^{1

2}, Yu Zhang³, Chaozhong Li⁴, Jinwu Wei⁴, Bin He^{1

2}, Hongjun Xu^{1

5}, Jihao Xia^{1

2}, Xuming Luo^{1

2}, Jiahui Li^{1

2}, Jing Dong^{1

5}, Wenqing He^{1

2}, Zhengren Yan^{1

2}, Wenlong Yang^{1

2}, Fusheng Ma⁶, Guozhi Chai⁴, Peng Yan⁷, Caihua Wan^{1

2}, Xiufeng Han^{1

2

5}, Guoqiang Yu^{8

9

10}

Affiliations

¹ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
² Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing, 100049, China.
³ Jiangsu Key Laboratory of Opto-Electronic Technology, School of Physics and Technology, Nanjing Normal University, Nanjing, 210046, China.
⁴ Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou, 730000, China.
⁵ Songshan Lake Materials Laboratory, Dongguan, Guangdong, 523808, China.
⁶ Jiangsu Key Laboratory of Opto-Electronic Technology, School of Physics and Technology, Nanjing Normal University, Nanjing, 210046, China. phymafs@njnu.edu.cn.
⁷ School of Electronic Science and Engineering and State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China.
⁸ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China. guoqiangyu@iphy.ac.cn.
⁹ Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing, 100049, China. guoqiangyu@iphy.ac.cn.
¹⁰ Songshan Lake Materials Laboratory, Dongguan, Guangdong, 523808, China. guoqiangyu@iphy.ac.cn.

Abstract

Ultrastrong and deep-strong coupling are two coupling regimes rich in intriguing physical phenomena. Recently, hybrid magnonic systems have emerged as promising candidates for exploring these regimes, owing to their unique advantages in quantum engineering. However, because of the relatively weak coupling between magnons and other quasiparticles, ultrastrong coupling is predominantly realized at cryogenic temperatures, while deep-strong coupling remains to be explored. In our work, we achieve both theoretical and experimental realization of room-temperature ultrastrong magnon-magnon coupling in synthetic antiferromagnets with intrinsic asymmetry of magnetic anisotropy. Unlike most ultrastrong coupling systems, where the counter-rotating coupling strength g₂ is strictly equal to the co-rotating coupling strength g₁, our systems allow for highly tunable g₁ and g₂. This high degree of freedom also enables the realization of normalized g₁ or g₂ larger than 0.5. Particularly, our experimental findings reveal that the maximum observed g₁ is nearly identical to the bare frequency, with g₁/ω₀ = 0.963, indicating a close realization of deep-strong coupling within our hybrid magnonic systems. Our results highlight synthetic antiferromagnets as platforms for exploring unconventional ultrastrong and even deep-strong coupling regimes, facilitating the further exploration of quantum phenomena.