Dirac mass induced by optical gain and loss

• 成果类型: Article
• 署名作者: Yu, Letian; Xue, Haoran; Guo, Ruixiang; Chan, Eng Aik; Terh, Yun Yong; Soci, Cesare; Zhang, Baile; Chong, Y. D.
• 署名单位: Nanyang Technological University; Chinese University of Hong Kong; Nanyang Technological University
• 刊物名称: Nature
• ISSN/ISSBN: 0028-5350
• DOI: 10.1038/s41586-024-07664-x
• 发表日期: 2024-08-01
• 关键词: symmetry

摘要

Mass is commonly considered an intrinsic property of matter, but modern physics reveals particle masses to have complex origins1, such as the Higgs mechanism in high-energy physics2,3. In crystal lattices such as graphene, relativistic Dirac particles can exist as low-energy quasiparticles4 with masses imparted by lattice symmetry-breaking perturbations5-8. These mass-generating mechanisms all assume Hermiticity, or the conservation of energy in detail. Using a photonic synthetic lattice, we show experimentally that Dirac masses can be generated by means of non-Hermitian perturbations based on optical gain and loss. We then explore how the spacetime engineering of the gain and loss-induced Dirac mass affects the quasiparticles. As we show, the quasiparticles undergo Klein tunnelling at spatial boundaries, but a local breaking of a non-Hermitian symmetry can produce a new flux non-conservation effect at the domain walls. At a temporal boundary that abruptly flips the sign of the Dirac mass, we observe a variant of the time-reflection phenomenon: in the non-relativistic limit, the Dirac quasiparticle reverses its velocity, whereas in the relativistic limit, the original velocity is retained. By using a photonic synthetic lattice, it can be experimentally demonstrated that Dirac masses can be induced by means of non-Hermitian perturbations based on optical gain and loss.