Spin-wave coupling to electromagnetic cavity fields in dysposium ferrite

Abstract

Coupling of spin-waves with electromagnetic cavity field is demonstrated in an antiferromagnet, dysprosium ferrite (DyFeO3). By measuring transmission at 0.2-0.35 THz and sweeping sample temperature, magnon-photon coupling signatures were found at crossings of spin-wave resonances with Fabry-Pérot cavity modes formed in samples. The obtained spectra are explained in terms of classical electrodynamics and a microscopic model. PACS numbers: 71.36.+c, 76.50.+g, 75.50.Ee Coupling of matter and electromagnetic radiation 1 is a topic of great interest in solid state physics research because of their hybrid quantum nature. 2 In the THz range, phonon-polaritons are a well-know example of a light-matter coupling. Recently, polaritons in the THz region were shown with intersubband transitions, 3,4 cyclotron resonance 5 and plasmons 6 in two-dimensional electron gases, as well as with intermolecular transitions in organic materials. 7 In these systems, a strong-coupling regime can be achieved when losses are smaller than the exchange rate between light and matter, 8 giving rise to the vacuum Rabi splitting. Polaritons are composite particles, which are studied in basic research on quantum optics, 2 and can be considered for use in quantum computing and quantum memories. 9-13 The coupling of electromagnetic cavity-modes to magnons was researched intensively in ferromagnets at GHz frequencies, 12,14,15 meeting with expectations of energy-efficient spintronic devices. 16 Coupling of magnons with superconducting qubits was also investigated. 17,18 The Purcell enhancement and the vacuum Rabi splitting were demonstrated in ferromagnetic materials. [19][20][21][22]

Coherent and Dissipative Cavity Magnonics

“…For example, strong coupling has now been achieved using the ferromagnetic metal permalloy, important for nanoscale spintronic development, 39,40 and several antiferromagnets. [43][44][45]54 From the cavity perspective, all that is required is a well defined resonance; 55 a variety of unique 3D cavity designs 28,29,[56][57][58][59][60] and 2D resonators 26,32,[61][62][63] have been used. Often cavity modes with quality factor Q 1000 are desired to help achieve high cooperativity.…”

“…32-38. Following the early advances of coherent cavity magnonics, the field grew rapidly between 2017 -2020. Amongst the important results of this period were the observation of dissipative coupling, 18 the realization of strong coupling in nanoscale ferromagnetic metals, 39,40 the exploration of exceptional points and the role of PT symmetry, 21,22,24,41,42 experimental studies of strong coupling in antiferromagnets, [43][44][45] and the advancement of quantum magnonics, enabling, for example, the quantum sensing of magnons. 10,11 These discoveries opened many new doors for cavity magnonics, which should provide years of fruitful discovery.…”

Antiferromagnetic cavity optomagnonics

“…The physics of AFMs in combination with electromagnetic cavities is just starting to be explored. Besides the mentioned experiments in the THz regime [25,26], strong coupling between MW photons and AFM magnons has been reported [32], while magnon dark modes [33] and coupling to ferromagnets [34] via a MW cavity have been proposed theoretically. In turn, methods involving light to probe and control AFMs are being developed [35,36].…”

“…Exciting developments have also emerged very recently in the THz regime, a frequency range which has been historically challenging due to the absence of efficient sources and detectors (the "THz gap") [21]. Strong light-matter coupling in the THz regime has been achieved employing cavities [22][23][24], including strong coupling to magnons in antiferromagnets (AFMs) [25,26], opening the door for quantum applications in the THz domain. Antiferromagnetic materials support magnons that can be described as excitations of a spin antialigned ground state (the Néel state) [27].…”

“…The tunability with a magnetic field, in particular, for tuning a magnon mode from dark to bright, shows promise for quantum protocols for quantum information storage and retrieval. The coherent coupling of THz magnons to optical photons could allow the implementation of a quantum transducer [26]. Here, we focused on one-magnon processes; two-magnon processes will be treated elsewhere.…”