Abstract

The chirality density of light fields is a product of the electric and magnetic fields and has been a useful concept in optics, e.g., for the separation of chiral molecules. Spintronics and orbitronics are distinct fields that focus on the transport of electrons' spin and orbital angular momentum in solids. Here, we bridge the two fields by predicting the transfer of optical chirality density into spin and orbital currents in conductors via the evanescent electromagnetic fields of excited magnetic nanostructures [1-5]. I will address three aspects of this effect:

1) The joint effect of the electric and magnetic fields results in a pure spin/orbital current flowing parallel to the magnet|conductor interface, rendering a Hall-type spin/orbital pumping with high efficiency [3,4].

2) The pumped longitudinal spin current becomes unidirectional when the circular polarization of the electromagnetic field is locked to its momentum, rendering the flow direction locked to the chirality of the field [2,4].

3) Extending our theory to superconductors, we predict the pumping of supercurrent in triplet superconductors by microwaves [5].

[1] Tao Yu and Gerrit E. W. Bauer, Noncontact Spin Pumping by Microwave Evanescent Fields, Phys. Rev. Lett 124, 236801 (2020).

[2] Chengyuan Cai and Tao Yu*, Spin Radiation of Electrons, Excitons, and Phonons, Phys. Rev. B  110, L180405 (2024).

[3] Chengyuan Cai, H. C. Wang, and Tao Yu*, Evanescent Orbital Pumping by Magnetization Dynamics Free of Spin-Orbit Coupling, arXiv:2504.05827. 

[4] Ping Li, Chengyuan Cai, and Tao Yu*, Hall and Unidirectional Spin Pumping, arXiv:2510.26208.

[5] Ping Li, Chengyuan Cai, and Tao Yu*, Conversion of magnon or photon spin angular momentum to spin supercurrent in superconductors, submitted.

Biography

Tao Yu, Tao Yu is a professor of Huazhong University of Science and Technology, China. He has been dedicated to theoretical research in the fields of magnetism, spintronics, orbitronics, unconventional superconductivity, and their interdisciplinary areas.

In recent years, a number of theoretical predictions by Yu's research group have been experimentally verified, including the Meissner magnon collective mode in superconductors, the giant frequency shift of ferromagnetic resonance in ferromagnet Josephson junctions, magnonic thermal transistors, hyperbolic excitation of ferroelectric magnons in ferroelectric materials, surface acoustic waves driven by magnetic dynamic excitations, magnetically induced unidirectional perfect absorption of microwaves, and the spin Seebeck effect of magnons in altermagnets.