Abstract-Laser-induced magnetization curve

Shintaro Takayoshi1, Masahiro Sato2, and Takashi Oka3

• 1National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
• 2Department of Physics and Mathematics, Aoyama-Gakuin University, Sagamihara, Kanagawa 252-5258, Japan
• 3Department of Applied Physics, The University of Tokyo, Hongo, Bunkyo, Tokyo 113-8656, Japan

https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=3111981911959611927

We propose an all optical ultrafast method to highly magnetize general quantum magnets using a circularly polarized terahertz laser. The key idea is to utilize a circularly polarized laser and its chirping. Through this method, one can obtain magnetization curves of a broad class of quantum magnets as a function of time even without any static magnetic field. We numerically demonstrate the laser-induced magnetization process in realistic quantum spin models and find a condition for the realization. The onset of magnetization can be described by a many-body version of Landau-Zener mechanism. In a particular model, we show that a plateau state with topological properties can be realized dynamically.

DOI: http://dx.doi.org/10.1103/PhysRevB.90.214413

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3 More

• Published 3 December 2014
• Received 3 February 2014
• Revised 14 November 2014

©2014 American Physical Society

Abstract-Magnetization and phase transition induced by circularly polarized laser in quantum magnets

Shintaro Takayoshi, Hideo Aoki, and Takashi Oka
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.085150#abstract

We theoretically predict a nonequilibrium phase transition in quantum spin systems induced by a laser, which provides a purely quantum-mechanical way of coherently controlling magnetization. Namely, when a circularly polarized laser is applied to a spin system, the magnetic component of a laser is shown to induce a magnetization normal to the plane of polarization, leading to an ultrafast phase transition. We first demonstrate this phenomenon numerically for an S=1 antiferromagnetic Heisenberg spin chain, where a new state emerges with magnetization perpendicular to the polarization plane of the laser in place of the topologically ordered Haldane state. We then elucidate its physical mechanism by mapping the system to an effective static model. The theory also indicates that the phenomenon should occur in general quantum spin systems with a magnetic anisotropy. The required laser frequency is in the terahertz range, with the required intensity being within a prospective experimental feasibility.

DOI: http://dx.doi.org/10.1103/PhysRevB.90.085150

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