Professor Ching-Ray Chang and his collaborators publish “Yang–Mills physics in spintronics” paper in <Physics Reports>

The National Taiwan University has, in an international team effort, collaborated with the Chinese Culture University, the University of Taipei, the National University of Singapore, the Royal Melbourne Institute of Technology, and the Tokyo Institute of Technology, to write a review article on the physics of Yang-Mills in spintronics. This article was recently published in the Physics Reports (Oct 2020).

Physics Reports has always been one of the academic journals with the highest impact factor in physics community. The 5-Year Impact Factor is 24.659, which is much higher than the 5-Year Impact Factor of Nature Physics (21.797). It is worth mentioning that the publication in Physics Reports, with Taiwanese authors, or even corresponding authors, is already rare. If it is related to condensed matter, this article can be said to be the first and only publication of Physics Reports since 1971. This paper is now available for download on the journal webpage.


Yang-Mills theory is the cornerstone of the standard model and is traditionally an area of great interest to high energy and mathematical physicists. Originally designed to explain the physics that permanently glue fundamental particles together, Yang-Mills has today expanded far beyond the realm of its original proposition. Concepts introduced in the high-energy model have now found useful applications in condensed matter as well as atomic and optical systems. In the 1990s, Yang-Mills-inspired physics expanded to spintronics – a modern field that straddles condensed matter and electron spin transport in very small devices. These devices are normally constructed out of materials with strong spin-orbit coupling, e.g. semiconductor, or the topological.

While review articles had been written on Yang-Mills in atomic and condensed matter physics, a consolidated summary of Yang-Mills-inspired spintronics – a role to be filled by this article, is clearly missing. This article started with an introduction of the history of the gauge physics as well as their modern manifestations in the Yang-Mills, the Aharonov-Bohm, the Aharonov-Casher, and the Berry-Pancharatnam effects. Yang-Mills-like physics is treated as a unifying context for numerous spin-orbit related phenomena, e.g. the spin Hall and the spin torque – this is in fact a consolidation of past efforts. However, what the authors think lacking in most previous work is an explicit elucidation of the links between Yang-Mills and the individual phenomena. Therefore, what we consider a fresh perspective in this review is a discussion carried out from the point of view of the force and the phase physics. For example, the spin force physics of the spintronic gauge is discussed in connection with the spin Hall, the spin jitter motion, the quantum spin Hall, and the spin torque. The spin phase physics is on the other hand discussed in the context of the spin interference and the persistent spin helix. It is simply remarkable that Yang-Mills is a unifying context, and the links could be plausibly explained by the simple physics of force and phase. To put things into perspective, gauge fields like the Berry-Pancharatnam, the Aharonov Bohm and the Aharonov Casher are also discussed alongside the Yang-Mills in terms of their forceful and forceless physics.

This article would be useful to condensed matter physicists, particularly those in the fields of nanosciences e.g. spintronics, topological systems, 2D graphene and silicene. Compared to the vast spectrum of theoretical approaches in the nanosciences and spintronics, the gauge theoretic is a small but an important part. This article provides a direct linkage of the gauge theoretic approaches to the spin and the magnetic phenomena. On the other hand, this article could also be useful to the community of gauge-field or high energy theorists seeking to venture into the world of condensed matter and nanosciences.

An illustration of the different types of Hall effects. The charge Hall effect is associated with the magnetic field. The spin Hall effect is associated with the Yang-Mills curvature via the spin longitudinal force. The anomalous Hall effect is associated with the local magnetization.