CAREER: Fundamental phenomena in magnon condensates

Non-technical abstract: Bosons are particles of integer spin that allow for the fundamental quantum effect of Bose-Einstein Condensation (BEC), which manifests as the spontaneous formation of a macroscopic coherent quantum state in an otherwise incoherent multi-particle system. The project will improve understanding of the BEC phenomenon in magnetic quasiparticles – magnons. This work may have a transformative effect on the fields of quantum information science, solid-state physics, and modern magnetism, as well as help maintain US leadership in the area of quantum information science and technology. This CAREER project explores ferromagnetic structures to understand magnon BEC properties and interactions with a dense magnon gas existing alongside it using state-of-the-art nanofabrication, optical, and microwave characterization techniques. The educational component of the project integrates contemporary research themes into existing graduate and undergraduate courses, creates new quantum physics and quantum information science lab courses, provides access to scientific developments to a broad community, and increases the number of students in STEM through the organization of scientific tournaments. Technical abstract: Despite many achievements in the field of magnon gases and condensates, like the observation of magnon supercurrents, Bogoliubov waves, Josephson effect, and second sound, there are many intriguing fundamental questions still open. One of them is how these phenomena are affected by boundaries or geometrical confinement, and what are the critical sizes of the system to support magnon BEC in ferromagnetic materials. The project combines state-of-the-art micro- and nano-structuring with optical Brillouin light scattering spectroscopy and introduces optical heating techniques at room as well as cryogenic temperatures. The project's aims are: (i) Experimentally observe and compare magnon BEC dynamics in conventional 3D, quasi-2D, and quasi-1D structures; (ii) Create a persistent condensed phase and determine its areas of existence; (ii) Study properties of magnon BEC in systems with periodic boundary conditions (rings); (iii) Create a complete joint model of magnon second sound and Bogoliubov waves in continuous and confined samples; (iv) Experimental observe and study magnon thermodynamic lasing effect. The project supports the training of undergraduate and graduate students in advanced optical spectroscopy techniques, cryogenics, and nanofabrication. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.