Nano-Imaging of Topological Semimetals using Sub-2 Kelvin Magnetic Scanning Near-Field Optical Microscopy*

We have developed a highly adaptable near-field microscopy platform capable of operating under both high magnetic fields and sub-liquid-helium temperatures with ultrafast excitations in the tunable range from terahertz to the mid-infrared spectral region. In this study, we conduct real-space imaging of the Dirac semimetal Zirconium pentatelluride (ZrTe5) and the Weyl semimetal Tantalum arsenide (TaAs). Our experimental setup enables us to acquire nano-imaging and nano-spectroscopy data over a range of magnetic fields, reaching up to 5 Tesla, and temperatures as low as 1.8K. Our data show high signal-to-noise ratios with a self-homodyne detection method. We will analyze findings in the context of Landau level transitions, the emergence of massive Dirac excitons, and the behavior of magneto-plasmons within these materials.