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Seminar: “Condensation of Magnons by Spin Seebeck Currents” (Lecture)

Date
Friday 7 September 2018Add to my calendar
Time
from 15:45
Location
HG00.068
Speaker
Dr. Igor Barsukov (University of California – Riverside)
Description

Igor BarsukovInjection of a pure spin current into magnetic insulator modifies the chemical potential of magnons, as demonstrated by recent experiments [1], and leads to intriguing phenomena such as long-range spin transport [2] and magnon condensation [3]. A pure spin current can be injected into magnetic insulator via spin Seebeck effect [4]. A temperature gradient at the interface of magnetic insulator and normal metal generates a non-equilibrium population of incoherent magnons. Nonlinear magnon interaction transfers the angular momentum from incoherent magnon cloud to a low-energy magnon state, thereby reducing its effective damping [3,5]. Above the critical magnitude of such thermal spin current, magnonic system undergoes a phase transition establishing a coherent low-energy magnonic state [3]. This process corresponds to bosonic condensation of non-equilibrium magnons, generated by incoherent heat transport process, into a coherent magnon condensate.

Such magnon condensate driven by thermal spin current has been recently realized in nanowires fabricated from bilayers of Yttrium Iron Garnet (YIG) and Platinum [5]. Via ohmic heating of the Pt layer, a temperature gradient is established across the YIG/Pt interface. The thermal spin current compensates the damping of YIG and creates a magnonic condensate that manifests through auto-oscillations of the lowest spin wave mode of the nanowire. The auto-oscillations generate a microwave signal by means of magnetoresistive effects in Pt that is measured spectroscopically. The experimental results demonstrate that magnon condensates can be created via incoherent drives and present a route for technological implementation. Energy loss due to ohmic heating is the major bottleneck for the performance of nanoelectronics devices. Thermally generated spin currents can be employed to harvest the waste heat and to operate spintronic devices, such as tunable microwave oscillators and spin wave emitters.

This work was supported by Spins and Heat in Nanoscale Electronic Systems (SHINES), an Energy Frontier Research Center funded by the US Department of Energy.

Refs.:
[1] Chunhui Du, T. van der Sar, T.X. Zhou, et al., Science 357, 195 (2017)
[2] D. Bozhko, A. Serga, P. Clausen, et al., Nat. Phys. 12, 1057 (2016)
[3] S. Bender and Y. Tserkovnyak, Phys. Rev. B 93, 064418 (2016)
[4] G.E.W. Bauer, E. Saitoh, B.J. van Wees, Nat. Mater. 11, 391 (2012)
[5] C. Safranski, I. Barsukov, H.K. Lee, et al., Nat. Commun. 8, 117 (2017)

Brief biography:
Igor Barsukov obtained Diploma (2006) in physics at Ruhr-University Bochum (Germany) working on magneto-thermal microscopy of ferromagnetic nanostructures. He received a Marie-Curie Fellowship (2006, 2007) and worked on microwave spectroscopy of magnetic thin films and nanoparticles at the Academy of Sciences in Prague (Czech Republic). He completed his Doctorate in physics (2012) at the University Duisburg-Essen (Germany) focusing on MBE, structure-magnetism correlation, and magnetic damping. He then joined University of California at Irvine as postdoctoral scholar to work on experimental spintronics. Since 2016, he has been Assistant Professor at the Physics Department and a participating faculty in the Materials Science and Engineering Program at the University of California, Riverside. His laboratory employs DC to THz spectroscopy to study spin dynamics and spin transport, with a focus on thermal spin currents, magnon condensates, and nonlinear spin dynamics.

Contact
prof. Alexey Kimel