Associate Professor Zhang Longlong Publishes a Featured Article in Applied Physics Letters
Recently, Professor Hao Yuying’s group had made progress in the field of Helicity-dependent all-optical magnetic switching. Associate Professor Zhang Longlong and Professor Hao Yuying published a featured article entitled Helicity-dependent all-optical switching based on the self-trapped triplet excitons in Applied Physics Letters, a top journal of applied physics.
All-optical switching technique is of great value in magnetic recording, magnetic memory, and quantum information processing. Different from the traditional approach switching the magnetization by the magnetic field, the magnetization is directly controlled by ultrafast laser pulses, while helicity-dependent all-optical switching also exploits the relationship between the polarization state of the laser pulse and the magnetization direction, i.e., the inverse Faraday effect. As shown in Figure 2, in a ferromagnetic array with magnetization initially aligned upward, a right-handed (σ−) CPP can reverse the magnetic domains in the spot to downward and a second left-handed (σ+) CPP can reverse the switched magnetic domains back to the initial state. In recent years, HD-AOS has been widely reported in ferromagnetic and ferrimagnetic alloys. However, it was seldom reported in the organic materials.
In this paper, a theoretical scheme was proposed to realize HD-AOS in organic polymers by means of dynamical simulations. Triplet excitons in polymers are characterized by their long lifetime and low mobility due to the easy formation of self-trapped states in the soft structure of the lattice. Also, due to the long spin relaxation time of organic system and its long-time spin coherent, it is a potential medium for HD-AOS. It is shown that the magnetization switching of STTE can be effectively achieved using femtosecond circularly polarized laser pulses at terahertz, and the switching shows obvious helicity-dependent (as is shown in Figure 3). At the same time, the magnetization switching can be repeated with multiple laser pulses, and each switching is completed within dozens of femtoseconds. The high magnetization switching ratio of the exciton can be achieved by optimizing the light parameters. This study provides a feasible way to realize the organic-based HD-AOS. The study was supported by the National Natural Science Foundation of China (Grant No. 11904254) and the Natural Science Foundation for Young Scientists of Shanxi Province (Grant No. 201901D211113).