image: Demonstration for the constructed large-scale meron lattices by magnetic force microscopy. view more
Credit: by Xuefeng Wu, Xu Li, Wenyu Kang, Xichao Zhang, Li Chen, Zhibai Zhong, Yan Zhou, Johan Åkerman, Yaping Wu, Rong Zhang, and Junyong Kang
Photon is one of the elementary particles in quantum mechanics. Effective manipulation and modulation of the quantum states is the cornerstone of various applications, such as quantum computing and quantum secure communication. The chiral photon source can in situ modulate the quantum state of light within the light source, which is beneficial for device integration and miniaturization. Therefore, the chiral photon source is considered an ideal light source in quantum technology.
Existing chiral photon sources typically engage spin-polarized materials to manipulate the spin angular momentum of electrons and photons. Even an external magnetic field or low-temperature environment is mostly required, the obtained polarization and stability are usually poor and susceptible to electromagnetic perturbations. Breaking through the above bottlenecks and further improving the polarization become a critical problem in developing high-performance chiral photon sources.
In an article published in Nature Electronics, the semiconductor research team at Xiamen University, led by Professor Junyong Kang, Professor Rong Zhang, and Professor Yaping Wu, along with other groups from Japan, China, and Sweden, proposed a new strategy of orbital regulated topological spin protection, breaking the bottleneck in stability of large-area topological meron lattices at room temperature and under zero magnetic field. They further used the topological lattices to effectively and successfully manipulate the spin angular momentum of electrons and photons and developed a topological spin light-emitting diode for the first time. This achievement realized the chirality transfer from topologically protected quasiparticles to Fermions and further to Bosons, paving a new pathway for quantum state manipulation and transmission. Xuefeng Wu, Xu Li, and Wenyu Kang are the co-first authors of this article.
1. Constructing large-scale topological meron lattices
Topology is an important concept in many fields, including mathematics, physics, chemistry. The topological spin structures, such as skyrmions and merons, have higher stability than conventional electronic materials due to their unique topological protection features. Introducing topological eigenstates into polarized photon sources has become a feasible solution to break through the stability bottleneck in polarized materials. However, the existing topological spin structures have constraints in lattice scale, ordering, and temperature or magnetic field requirements, which cannot meet the needs of device applications.
The team proposed a new principle of orbital-regulated topological protection in electron spin. Based on the theoretical simulation, the team proved that applying a strong magnetic field during crystal growth could enhance and freeze the orbital coupling, thereby improving the crystalline ordering and inducing strong Dzyaloshinsky Moriya interactions. These changes will facilitate the nucleation of large-scale topological lattices and overcome their stability problems at room temperature and under zero external fields.
Under the guidance of this innovative idea, the team designed and built a high magnetic field-assisted molecular-beam epitaxy equipment, which was later patented in China and the United States. After a systematic material selection, large-scale, long-range ordered topological meron lattices were successfully grown on the wide bandgap semiconductor substrate. The lattices have high stability at room temperature and under zero magnetic field, laying a solid foundation for subsequently developing the topological solid-state light source.
2. Solving the problem of topologically-protected chirality transfer
Topological spin structures are promising information carriers for future high-density, high-throughput, and low-power devices. Nonetheless, their applications in semiconductor optoelectronics have not yet been explored. The current research has effectively manipulated topological spin structures using light and spin current (such as race-track memories, skyrmion logic gates, etc.). How about the reverse process? Can the topological spin structures manipulate electrons and photons?
Through an in-depth theoretical and experimental investigation, the team found that when electrons are injected into the meron lattices and semiconductor, their trajectory can be effectively controlled, thereby producing a spin polarization and achieving highly polarized photon emission. This result proved that the topological quasiparticle can transfer chirality to electrons and photons. The new topological solid-state light source chip has distinct quantum characteristics and is expected to meet the needs of future quantum technology.
The HMF-MBE method proposed in this work can manipulate the interactions within strong-correlated materials through orbital control. This method can be widely applied to the controllable growth of other crystals and topological lattices, such as skyrmions and vortices. The large-scale topological meron lattices created in this work have room-temperature and zero-field stability, which will provide an ideal platform for the frontiers of photonics research.
Besides, this work has created an on-chip chiral photon source, which can transfer chirality from topologically protected quasiparticles to Fermions with mass and further to massless Bosons. This achievement has scientific significance for the practical applications of topological spin structures.