Chemical potential of quasi-equilibrium magnon gas driven by pure spin current

• Type of Material: Article
• Authors: V.E. Demidov, University of Muenster; Sergei Urazhdin, Emory University; B. Divinskiy, University of Muenster; V.D. Bessonov, Institute of Metal Physics; V.V. Ustinov, Institute of Metal Physics; S.O. Demokritov, University of Muenster
• Language: English
• Date: 2017-11-17
• Publisher: Nature Publishing Group: Nature Communications
• Publication Version: Final Published Version
• Copyright Statement: © The Author(s) 2017
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1038/s41467-017-01937-y
• Title of Journal or Parent Work: Nature Communications
• ISSN: 2041-1723
• Volume: 8
• Grant/Funding Information: This work was supported by the Deutsche Forschungsgemeinschaft, the NSF Grant Nos. ECCS-1509794 and DMR-1504449, and the program Megagrant No. 14.Z50.31.0025 of the Russian Ministry of Education and Science.
• Research Categories: Physics, General

Abstract

Pure spin currents provide the possibility to control the magnetization state of conducting and insulating magnetic materials. They allow one to increase or reduce the density of magnons, and achieve coherent dynamic states of magnetization reminiscent of the Bose–Einstein condensation. However, until now there was no direct evidence that the state of the magnon gas subjected to spin current can be treated thermodynamically. Here, we show experimentally that the spin current generated by the spin-Hall effect drives the magnon gas into a quasi-equilibrium state that can be described by the Bose–Einstein statistics. The magnon population function is characterized either by an increased effective chemical potential or by a reduced effective temperature, depending on the spin current polarization. In the former case, the chemical potential can closely approach, at large driving currents, the lowest-energy magnon state, indicating the possibility of spin current-driven Bose–Einstein condensation.