Chirality as Generalized Spin-Orbit Interaction in Spintronics

Abstract

Chirality or handedness is a digital relation between three vectors that distinguishes an object from its mirror image, such as the spread fingers of the right and left hand. The chirality of ground state magnetic textures defined by the vectors of magnetization, its gradient, and an electric field from broken inversion symmetry can be fixed by a strong relativistic spin-orbit interaction. This review focuses on the chirality observed in the excited states of the magnetic order, dielectrics, and conductors that hold transverse spins when they are evanescent. Even without any relativistic effect, the transverse spin of the evanescent waves are locked to the momentum and the surface normal of their propagation plane. This chirality thereby acts as a generalized spin-orbit interaction, which leads to the discovery of various chiral interactions between magnetic, phononic, electronic, photonic, and plasmonic excitations in spintronics that mediate the excitation of quasiparticles into a single direction, leading to phenomena such as chiral spin and phonon pumping, chiral spin Seebeck, spin skin, magnonic trap, magnon Doppler, and spin diode effects. Intriguing analogies with electric counterparts in the nano-optics and plasmonics exist. After a brief review of the concepts of chirality that characterize the ground state chiral magnetic textures and chirally coupled magnets in spintronics, we turn to the chiral phenomena of excited states. We present a unified electrodynamic picture for dynamical chirality in spintronics in terms of generalized spin-orbit interaction and compare it with that in nano-optics and plasmonics. Based on the general theory, we subsequently review the theoretical progress and experimental evidence of chiral interaction, as well as the near-field transfer of the transverse spins, between various excitations in magnetic, photonic, electronic and phononic nanostructures at GHz time scales. We provide a perspective for future research before concluding this article.

Topological states in chiral electronic chains

“…Chiral structures have attracted considerable interest. Examples are chiral magnets, chiral metals or chiral molecules, for instance in the context of chiral induced selective spin transport 1 . Molecules such as DNA or similar structures, either single stranded or doubly stranded, have been studied [2][3][4][5][6][7][8][9][10][11][12][13][14] .…”

Chiral coupling between a ferromagnetic magnon and a superconducting qubit

“…In recent years, chiral phenomena have been attracting intense attentions in quantum optics [1][2][3]. Chirality refers to the breaking of inversion symmetry [4,5], and plays very important roles in various fields of science and technology, such as molecule detection [6][7][8], optical communication and information processing [9,10]. A central issue in this subject is to tailor chiral couplings [11][12][13][14], which can be used to control the directionality of the spontaneous emission and modify the interactions between multiple quantum emitters [15].…”