image: Schematic dispersion relations for bicircular light drive phase transition from a nodal-line semimetal to a Weyl semimetal. The energy and momentum separation of opposite chiral Weyl nodes can be dynamically controlled via changing bicircular light polarization state. The proposed setup for a gyrotropic current driven by trefoil bicircular light, which is the superposition of two opposite chirality circularly polarized ligh with different frequencies marked as ω and 2ω.
Credit: ©Science China Press
Recent years have witnessed a surge of interest in topological semimetals due to their unique electronic band structures and exotic quantum phenomena. A less explored but fundamentally important response is the gyrotropic magnetic effect (GME), which can occur in inversion (P) symmetry broken Weyl semimetals under a dynamic magnetic field. While the GME represents a basic property of Bloch electrons in a system with P-symmetry breaking, it remains unexplored experimentally. The obstacle to measurements of GME possibly attributes to the fact that inversion symmetry broken Weyl semimetals typically possess time-reversal (T) symmetry. The combination of T symmetry and additional crystalline symmetries enforces that the energy difference between Weyl nodes with opposite chirality is zero, naturally vanishing the gyrotropic current in these T-invariant Weyl semimetals. The intrinsic chiral semimetals, such as CoSi and AlPt, which host topological nodes at different energies, are natural candidates for the GME. However, these materials typically possess multiple pairs of Weyl nodes near the Fermi level, and the resulting superposition of their individual GME contributions can complicate the interpretation and direct detection of the effect. To avoid such mishaps and ensure the observation of a visible gyrotropic current, it is highly desirable to design an ideal Weyl semimetal candidate that hosts a single pair of Weyl nodes with a sizable energy difference near the Fermi level.
Recently, the research team led by Prof. Rui Wang and Prof. Dong-Hui Xu from Chongqing University has theoretically revealed a new pathway to achieve the GME: irradiating an anisotropic nodal-line semimetal with bicircular light. This scheme ingeniously utilizes the light-induced breaking of spatial symmetries to create a system containing only a single pair of significantly energy-separated Weyl nodes, thereby generating a pronounced and easily identifiable gyrotropic magnetic current signal. Combining first-principles calculations with Floquet theory, the research team identified black phosphorus as an ideal candidate material platform. The intrinsic anisotropy of its crystal structure significantly enhances the GME response, generating a current that reaches detectable levels on the order of μA/μm2. The study also shows that this current can be continuously tuned by adjusting the polarization state and intensity of the bicircular light and demonstrates the feasibility of realization under existing laser technology and measurement conditions. This work not only provides a clear path for the experimental observation of the elusive GME in real materials but also opens new avenues for exploring the interplay of light, symmetry, and topology in quantum materials.
The results of this work have been published in Science Bulletin.
Journal
Science Bulletin
Method of Research
Computational simulation/modeling