News.hust.edu.cn (Correspondent: Liu Huan) On April 12, the journal Science published the research findings of Zhu Xuefeng, associate professor of School of Physics, in collaboration with Stanford University and the National University of Singapore: Anti-parity-time symmetry in diffusive systems. Peng Yugui, a doctoral student from school of physics, was the co-first author and associate professor Zhu Xuefeng was the co-corresponding author of this paper.

Symmetry is particularly common in daily life and in nature, and the laws of physics also satisfy beautiful symmetry. After a long period of exploration and accumulation, physicists have reached a consensus that symmetry and conservation laws always appear together. For a particular system, the intrinsic symmetries of its physical laws should be studied in depth if conservation laws that do not vary with certain conditions are to be obtained. At present, most symmetries-related researches are focused on the classical wave system, and there are few symmetries related to the diffusion system. The research findings of Zhu Xuefeng et al. put forward for the first time a new symmetry in the heat diffusion system, namely anti-parity-time symmetry and proved the existence of anti-parity-time symmetry experimentally.

The team found that when the thermal diffusion system was in an anti-parity-time symmetric phase, the drag effect of the mechanical motion in background carriers was suppressed and the distribution of temperature field remained stable. In the experiment, they constructed a pair of low thermal conductivity rings with thermal coupling that rotate in the opposite direction at the same speed, and observed the evolution of temperature field with time when the rotating speed of the ring was adjusted to a fixed value；when the rotation speed was relatively low, the anti-parity time symmetry condition was satisfied, and a stable distribution of thermal temperature field was observed. The position of temperature maximum did not evolve with the rotation of the ring. However, when the rotation speed was high, anti-parity-time symmetry breaks, and the observed temperature field distribution was no longer stable, and the position of temperature maximum would rapidly evolve with time.

Although a lot of theoretical work has discussed various implementation schemes of anti-parity-time symmetry, this work was the first time to observe completely different physical phenomena before and after the break of anti-parity-time symmetry phase. This study created a new field for the study of diffusion systems such as strong scattering systems, mass transport systems and heat conduction systems, and provided a new paradigm for the extension of symmetry theory to other systems besides the wave system.

Associate professor Zhu Xuefeng was a young teacher introduced by school of physics in 2014. Previously, he was elected to the "Bird's Nest Program" of Huazhong University of Science and Technology in 2011. Later, he studied with academician Zhang Xiang, one of the world's most famous scientists of metamaterials in University of California, Berkeley, the United States, and engaged in the research on acousto-optic metamaterials and energy-flow regulation. Peng Yugui, an undergraduate of Grade 2010 in school of physics, became the first direct doctoral student recommended by associate professor Zhu Xuefeng in 2014. At present, as the first author (including co-authors), he has published 6 papers of high-level achievements in international authoritative journals such as Science, Nature Materials, Nature Communications and Physical Review Letters. The work was supported by the general program and major programs of the National Natural Science Foundation of China, and the Bird's Nest Program of Huazhong University of Science and Technology.

Full text links：https://science.sciencemag.org/content/364/6436/170