Towards control of spin currents in magnetic insulators

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Date: February 10, 2022
Time: 3:45 p.m. - 5:00 p.m.
Location: Zoom
Category: Seminar

Towards control of spin currents in magnetic insulators

Speaker: Alexey Kovalev

Associate Professor

Department of Physics & Astronomy, the University of Nebraska-Lincoln


An ability to control spin currents is important for probing many spin related phenomena in the field of spintronics and for designing logic and memory devices with low dissipation. Spin-orbit torque is an important example in which spin current flows across magnetic interface and helps to control magnetization dynamics. As spin can be carried by electrons, spin-triplet pairs, Bogoliubov quasiparticles, magnons, spin superfluids, spinons, etc., studies of spin currents can have implications across many disciplines. In this talk, I will first discuss transport, Hall-like responses of magnons in antiferromagnetic insulators, ranging from collinear antiferromagnets [1,2,3] to breathing pyrochlore noncollinear antiferromagnets [4,5]. The theory also applies to noncollinear antiferromagnets, such as kagome, where we predict both the spin Nernst response [4] and the generation of nonequilibrium spin polarization [5] by temperature gradients, the latter effect constitutes the magnonic analogue of the Edelstein effect of electrons. I will further discuss the spin superfluid transport associated with collective modes in magnetic insulators [6,7]. We observe that in two dimensional systems at finite temperatures spin superfluidity is affected by the presence of topological defects. We further propose to use the Hall response of topological defects, such as merons and antimerons, to spin currents in 2D magnetic insulator with in-plane anisotropy for identification of the Berezinskii-Kosterlitz-Thouless (BKT) transition in a transistor-like geometry. Our numerical results relying on a combination of Monte Carlo and spin dynamics simulations show transition from spin superfluidity to conventional spin transport, accompanied by the universal jump of the spin stiffness and exponential growth of the transverse vorticity current. We propose a superfluid spin transistor in which the spin and vorticity currents are modulated by tuning the in-plane magnet across BKT transition, e.g., by changing the exchange interaction, magnetic anisotropy, or temperature [8].

 [1] V. Zyuzin, A.A. Kovalev, Phys. Rev. Lett. 117, 217203 (2016).

[2] Y. Shiomi, R. Takashima, E. Saitoh, Phys. Rev. B 96, 134425 (2017)

[3] B. Li, A.A. Kovalev. Phys. Rev. Lett. 125, 257201 (2020)

[4] B. Li, S. Sandhoefner, A.A. Kovalev, arXiv:1907.10567 (2019)

[5] B. Li, A. Mook, A. Raeliarijaona, A.A. Kovalev, arXiv:1910.00143 (2019)

[6] G. G. Baez Flores, A.A. Kovalev, M. van Schilfgaarde, K. D. Belashchenko, Phys. Rev. B 101, 224405 (2020)

[7] B. Li, A.A. Kovalev, Phys. Rev. B 103, 060406 (2021)

[8] E. Schwartz, B. Li, A.A. Kovalev, arXiv:2112.14241v1

Biography: Prof. Kovalev is a theoretical condensed matter physicist working on theoretical spintronics that comprises various classical and quantum phenomena related to the spin degree of freedom. Prof. Kovalev was appointed as an Assistant Professor at Department of Physics and Astronomy, the University of Nebraska-Lincoln in 2013, and promoted to an Associate Professor in 2019. He received his Master of Science in Physics from Moscow Institute of Physics & Technology, Russia. He has received his Ph.D. degree in Physics from Delft University of Technology in 2006. Prof. Kovalev worked as a research associate (Post-Doc) in between 2006 and 2008 at Texas A&M University, and in between 2008 and 2010 at UCLA. He has received Nebraska EPSCoR First Award at 2014 and DOE Early Career Award at 2015.


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Takeshi Sakaomto


February 2022