X. Hu, K. P. Wong, L. Zeng, X. Guo, T. Liu, L. Zhang, Q. Chen, X. Zhang, Y. Zhu, K. H. Fung, S. P. Lau
ACS Nano, Article ASAP (2020)
Topological Dirac semimetals made of two-dimensional transition-metal dichalcogenides (TMDCs) have attracted enormous interest for use in electronic and optoelectronic devices because of their electron transport properties. As van der Waals materials with a strong interlayer interaction, these semimetals are expected to support layer-dependent plasmonic polaritons yet to be revealed experimentally. Here, we demonstrate the apparent retardation and attenuation of mid-infrared (MIR) plasmonic waves in type-II Dirac semimetal platinum tellurium (PtTe2) nanoribbons and nanoflakes by near-field nanoimaging. The attenuated dispersion relations for the plasmonic modes in the PtTe2 nanoribbons (15–25 nm thick) extracted from the near-field standing-wave patterns are applied for the fitting of PtTe2 permittivity in the MIR regime, indicating that both free carriers and Dirac fermions are involved in MIR light–matter interaction in PtTe2. The annihilation of plasmonic modes in the ultrathin (<10 nm) PtTe2 is observed and analyzed, which manifests no near-field resonant pattern due to the intrinsic layer-dependent optoelectronic properties of PtTe2. These results could pave a potential wave for MIR photodetection and modulation with TMDC semimetals.