1.Development of a High-Performance, General-Purpose Magneto-Infrared Spectroscopy System

We have carried out long-term, systematic development of magneto-infrared spectroscopy instrumentation, realizing a general-purpose system compatible with both superconducting and resistive magnets, thereby addressing the fundamental issue of availability. Building upon this platform: (i) an external detection configuration was proposed, achieving full infrared spectral coverage from 1–200 μm under high magnetic fields; (ii) an imaging-based magneto-infrared architecture was developed, improving the signal-to-noise ratio; (iii) an in-situ polarization scheme was established, enabling polarization-resolved magneto-infrared spectroscopy. The system currently operates with simultaneous capabilities of 0-12 T magnetic field, 2-300 K temperature, 1-200 μm wavelength range, signal-to-noise ratio of 2×104, spectral resolution of 0.02 meV, and in-situ linear/circular polarization resolution, and has been providing long-term open access to users across disciplines worldwide.

…, Xiang Yuan*, A high-flux and high-efficiency setup for magneto-infrared spectroscopy. Review of Scientific Instruments, 96 (11): 113902. (2025)

…, Xiang Yuan*, In-situ polarimetry in collimated magneto-infrared spectroscopy system. Advanced Science Instruments, 1(1), 100005. (2026)

2.Magnetic-Field-Induced Topological States in New Dimensions

      Experimental studies of topological semimetals and chiral fermions are typically restricted to specific spatial dimensions. For example, Weyl fermions, as massless chiral fermions, have been extensively studied in three dimensions, although theory allows their existence in all odd dimensions. Using magneto-infrared spectroscopy under strong magnetic fields, we discovered in HfTe5 a magnetic-field-induced phase transition from a three-dimensional topological insulator to a one-dimensional Weyl semimetal, dominated by orbital ordering. This led to the experimental observation of one-dimensional Weyl fermions and verification of the one-dimensional relativistic optical conductivity formula predicted in condensed matter theory. In EuCd2As2, we further identified a magnetic-field-induced three-dimensional van Hove singularity governed by spin ordering, thereby overturning the conventional understanding that such singularities exist only in two dimensions.

…, Xiang Yuan*, Topological Lifshitz transition and one-dimensional Weyl mode in HfTe5. Nature Materials, 22, 84-91. (2023)

…, Xiang Yuan*, The discovery of three-dimensional Van Hove singularity. Nature Communications, 15, 2313. (2024)

3.Novel Infrared Device Principles under Magnetic Fields

     Circular dichroism reflects structural or electronic chirality in materials. However, in conventional systems, including magnetic materials, chiral crystals, and artificial metamaterials, circular dichroism is typically weak and spectrally narrow. Using magneto-infrared spectroscopy under strong magnetic fields, we experimentally induced and observed giant, broadband circular dichroism in bulk MnBi2Te4, arising from particle-hole symmetry breaking. This work establishes a new mechanism for optical chiral discrimination and introduces a novel route for tuning topological materials via particle–hole symmetry engineering.

…, Xiang Yuan*, Giant and broadband circular dichroism from particle-hole symmetry breaking in Weyl semimetal. Nature Materials, in press. (2026)

Other Interdisciplinary Studies, Facility Service, and Early Representative Works

…, Xiang Yuan*, Giant superlinear power dependence of photocurrent based on layered Ta2NiS5 photodetector. Advanced Science, 10, 2300413. (2023)

…, Xiang Yuan*, Transmission infrared micro-spectroscopic study of individual human hair, Journal of Biomedical Optics, 28(11), 116501. (2023)

…, Xiang Yuan*, … Memristive switching in the surface of a charge–density–wave topological semimetal. Science Bulletin, 69(13), 2042-2049. (2024)

…, Xiang Yuan*, … Observation of quantum oscillations near the Mott-Ioffe-Regel limit in CaAs3. National Science Review, 11(12) nwae127. (2024)

…, Xiang Yuan#, … Quantum Hall effect based on Weyl orbits in Cd3As2. Nature, 565(7739), 331–336. (2019)

…, Xiang Yuan#, … Ultrahigh conductivity in Weyl semimetal NbAs nanobelts. Nature Materials, 18(5), 482–488. (2019)

Xiang Yuan, … Chiral Landau levels in Weyl semimetal NbAs with multiple topological carriers. Nature Communications, 9(1), 1854. (2018)

Xiang Yuan, … The discovery of dynamic chiral anomaly in a Weyl semimetal NbAs. Nature Communications, 11(1), 1259. (2020)