Quantum Anomaly in a Topological Weyl Ferromagnet
Fermionic zero modes emerge at all length scales in various physical systems, such as the electroweak Z-string, 3He vortices, and cosmic strings, unveiling the secrets of quantum fluctuations in the vacuum and quantum anomalies associated with non-conserved particles, charges, and chiralities. Such zero modes manifest as the unique n = 0 Landau level in a topological Weyl ferromagnet, giving rise to non-conserved chiral charges and a consequently enhanced conductivity under parallel electric and magnetic fields – a phenomenon referred to as the chiral anomaly.
In a collaborative study led by Dr. Wei-Li Lee’s group at IoPAS and Prof. Guang-Yu Guo’s group at NTU, the chiral anomaly and its angular dependence were rigorously examined in a patterned device fabricated from thin films of the ferromagnetic topological Weyl metal SrRuO₃ (SRO). The thin films were grown using a cutting-edge oxide molecular beam epitaxy technique and exhibited exceptionally low residual resistivity at low temperatures, enabling the observation of unusual angular magnetoconductivity and Hall behaviors under various applied electric- and magnetic-field orientations. These results not only provide strong evidence for the dominance of the chiral anomaly effect but also demonstrate intriguing magnetic-field-tunable Weyl nodes in ferromagnetic Weyl SRO thin films. The complete data and analysis have been published in npj Quantum Materials.
Journal Links: https://www.nature.com/articles/s41535-026-00882-8