Dongwook Go: Nonequilibrium Orbital Angular Momentum for Spintronics

Lecturer
  • Dongwook Go
Place
Cukrovarnická Site
Event language
English
Date
2/22, 10:00–14:00

Dongwook Go

Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich, Germany

Nonequilibrium Orbital Angular Momentum for Spintronics

The key functionality required for spintronic devices is reading and manipulating magnetic configurations by an electrical current. A decade ago, the discovery of current-induced spin-orbit torque revolutionized the field of spintronics [1], where the spin-orbit coupling in a material enables the interaction between an electrical current and magnetic moments. A well-known mechanism of spin-orbit torque is due to nonequilibrium spin density by an external electric field in locally asymmetric environment [2]. Fundamentally, conduction electrons carry angular momentum in both spin and orbital parts of the wave function. As is well known, however, the orbital quenching – lifting of the orbital degeneracy by crystal field – suppresses the orbital angular momentum (OAM) in equilibrium, which may be the reason why OAM has not received the attention that it deserves in the magnetism and spintronics research. One question that remains to be answered is whether OAM in nonequilibrium may be induced and interact with magnetic moments.

In the first part of the talk, I will present a pedagogical introduction to recent progress on the generation and detection of nonequilibrium OAM [3] as well as its utilization for manipulating magnetic moments [4]. I will explain mechanisms of electrically inducing OAM density and its current, orbital current, and why their responses are much stronger than the spin counterparts. I will also discuss broad range of material candidates, which are not limited to materials containing heavy elements – a promising feature for sustainable and environment-friendly device applications [5].

In the second part of the talk, I will delve into a major fundamental challenge that we face: Distinguishing the orbital and spin contributions, which phenomenologically behave in a very similar way. I will explain how microscopic theories based on the electronic structure can help understanding underlying mechanisms of angular momentum transfer [6]. As an example, I will explain a recent theoretical prediction of long-range response of OAM [7] and examine recent experimental evidence [8]. At the end of the talk, I will discuss perspectives on the emerging research field of orbitronics and its potential impact on other fields that go beyond spintronics [9].

 

References:

  1. Miron et al. Nature 476, 189 (2011); Liu et al. Science 336, 5559 (2012); Manchon et al. Rev. Mod. Phys. 91, 035004 (2019).
  2. Wadley et al. Science 351, 587 (2016); Železný et al. Phys. Rev. B 95, 014403 (2017).
  3. Go et al. Phys. Rev. Lett. 121, 086602 (2018); Go et al. Phys. Rev. B 103, L121113 (2021).
  4. Go and Lee, Phys. Rev. Research 2, 013177 (2020).
  5. Jo et al. Phys. Rev. B 98, 214405 (2018); Salemi and Oppeneer, Phys. Rev. Materials 6, 95001 (2022).
  6. Go et al. Phys. Rev. Research 2, 033401 (2020).
  7. Go et al. arXiv:2106.07928.
  8. Liao et al. Phys. Rev. B 105, 104434 (2022); Hayashi et al. arXiv:2202.13896; Bose et al. arXiv:2210.02283.
  9. Go et al. Europhys. Lett. 135, 37001 (2021).