In condensed matter physics, an emerging research area involves controlling material properties using light, offering new opportunities for high-speed, energy-efficient, and contactless manipulation. In spintronics, for example, the optical control of magnetization and spins in magnets has given rise to the field of photodriven quantum spin systems, which has witnessed rapid progress in recent years, particularly with advances in laser technologies.

However, compared with the interaction between light and electronic charge, the interaction between light and electron spin is significantly weaker—about two orders of magnitude smaller in terms of energy. Consequently, photodriven excitation and control of spins have remained extremely challenging.

Recent developments have transformed this situation. The discovery of novel magnetic materials, such as multiferroics, Kondo-lattice magnets, Rashba electron systems, and magnetic Weyl semimetals, has made it possible to control spin dynamics via light electric fields. In parallel, new light sources, such as high-intensity terahertz radiation, and advanced measurement techniques, like spatiotemporal spin imaging, have enabled observation of nonlinear responses and coherent control of magnetization that were previously inaccessible.

Reflecting these advancements, a new Special Topics edition of the Journal of the Physical Society of Japan presents seven articles by leading theorists and experimentalists, highlighting recent progress and future perspectives of the field.

Mikuni and Satoh et al. present analytical solutions for the resonance dynamics of ferrimagnets that successfully reproduce experimental temperature-dependent behaviour both near and far from the compensation temperature.

Nikuni and Mizukami et al. review past studies and recent advances on circularly polarized laser-induced magnetization dynamics in metals, shedding light on optical torques and ultrafast spin–orbit coupling.

Takayoshi and Oka present an overview of quantum tunnelling driven by external fields, focusing on the role of geometric effects. They discuss the Landau–Zener model and the Schwinger effect and introduce the twisted Landau–Zener model and Keldysh crossover.

Masahito Mochizuki reviews recent theoretical progress in the optical control of magnetism in spin-charge coupled systems, including photoinduced magnetic phase transitions in irradiated double-exchange models, highly efficient spin polarization in Rashba systems, and electromagnon excitations in multiferroic materials.

Yoshikawa, Ogawa, and Shimano explore all-optical switching of magnetization in ferromagnetic materials and all-optical chirality switching in a ferromagnetic Weyl semimetal, as well as terahertz-light control of Hall effects.

Zhang, Watanabe, and Hirori summarize recent progress in ultrafast spin excitation in antiferromagnets by using terahertz pulses, outline the generation of intense terahertz magnetic near-field pulses using metallic metamaterials, and report the observation of nonlinear spin dynamics in perovskite-type holmium iron oxide.

Finally, Sato and Ikeda discuss theoretical formulations of Floquet Engineering in open quantum and classical systems, analyzing the dynamics of periodically driven dissipative systems using the quantum master equation and Fokker–Planck equation. They also introduce several representative examples of Floquet Engineering in various systems.

The wide range of topics covered in this Special Topics edition offers a comprehensive understanding of light-spin interactions. Continuous research in this field has the potential to open a new paradigm of light-driven materials design, which may revolutionize future information, energy, and environmental technologies.

Share this topic

Fields

Related Articles