Observation of the magnonic Dicke superradiant phase transition

• DOI: 10.1126/sciadv.adt1691
• Publication Date: 2025-04-04T17:59:14Z
• Authors: Dasom Kim; Sohail Dasgupta; Xiaoxuan Ma; Joong-Mok Park; Hao-Tian Wei; Xinwei Li; Liang Luo; Jacques Doumani; Wanting Yang; Di Cheng; Richard H. J. Kim; Henry O. Everitt; Shojiro Kimura; Hiroyuki Nojiri; Jigang Wang; Shixun Cao; Motoaki Bamba; Kaden R. A. Hazzard; Junichiro Kono
• Keywords: Diamagnetism; Magnon

Two-level atoms ultrastrongly coupled with single-mode cavity photons are predicted to exhibit a quantum phase transition, entering in which both the atomic polarization and photonic field finite even without external driving. However, this phenomenon, superradiant transition (SRPT), is forbidden by no-go theorem due existence of diamagnetic term. Here, we present spectroscopic evidence for magnonic SRPT ErFeO 3 , where role mode (two-level atoms) played an Fe 3+ magnon (Er spins). The absence term -Er exchange coupling ensures that does not apply. Ultrabroadband terahertz gigahertz magnetospectroscopy experiments revealed signatures thermal equilibrium, kink softening, respectively, two spin-magnon hybridized modes at critical point. Systems near expected harbor large-scale squeezing, will potentially provide route next-generation technologies.