Emergent topological Dirac semimetals afford fresh pathways for optoelectronics, although device implementation has been elusive to date. Specifically, palladium ditelluride (PdTe2) combines the capabilities provided by its peculiar band structure, with topologically protected electronic states, with advantages related to the occurrence of high-mobility charge carriers and ambient stability. Here, we demonstrate large photogalvanic effects with high anisotropy at terahertz frequency in PdTe2-based devices. A responsivity of 10 A/W and a noise-equivalent power lower than 2 pW/Hz0.5 are achieved at room temperature, validating the suitability of PdTe2-based devices for applications in photosensing, polarization-sensitive detection, and large-area fast imaging. Our findings open opportunities for exploring uncooled and sensitive photoelectronic devices based on topological semimetals, especially in the highly pursuit terahertz band.

The advent of topological semimetals enables the exploitation of symmetry-protected topological phenomena and quantized transport. Here, we present homogeneous rectifiers, converting high-frequency electromagnetic energy into direct current, based on low-energy Dirac fermions of topological semimetal-NiTe2, with state-of-the-art efficiency already in the first implementation. Explicitly, these devices display room-temperature photosensitivity as high as 251 mA W−1 at 0.3 THz in an unbiased mode, with a photocurrent anisotropy ratio of 22, originating from the interplay between the spin-polarized surface and bulk states. Device performances in terms of broadband operation, high dynamic range, as well as their high sensitivity, validate the immense potential and unique advantages associated to the control of nonequilibrium gapless topological states via built-in electric field, electromagnetic polarization and symmetry breaking in topological semimetals. These findings pave the way for the exploitation of topological phase of matter for high-frequency operations in polarization-sensitive sensing, communications and imaging.

Despite the considerable effort, fast and highly sensitive photodetection is not widely available at the low-photon-energy range (~meV) of the electromagnetic spectrum, owing to the challenging light funneling into small active areas with efficient conversion into an electrical signal. Here, we provide an alternative strategy by efficiently integrating and manipulating at the nanoscale the optoelectronic properties of topological Dirac semimetal PtSe2 and its van der Waals heterostructures. Explicitly, we realize strong plasmonic antenna coupling to semimetal states near the skin-depth regime (λ/104), featuring colossal photoresponse by in-plane symmetry breaking. The observed spontaneous and polarization-sensitive photocurrent are correlated to strong coupling with the nonequilibrium states in PtSe2 Dirac semimetal, yielding efficient light absorption in the photon range below 1.24 meV with responsivity exceeding ∼0.2 A/W and noise-equivalent power (NEP) less than ~38 pW/Hz0.5, as well as superb ambient stability. Present results pave the way to efficient engineering of a topological semimetal for high-speed and low-energy photon harvesting in areas such as biomedical imaging, remote sensing or security applications.

Two-dimensional (2D) materials have excellent electronic and optoelectronic properties, such as ultrafast charge transport and tunable photon absorption. These 2D materials include topological semimetal graphene, semiconductor material black phosphorus, transition-metal dichalcogenides, etc. Studying the ultra-high optical response speed and sensitivity, broadband spectrum and other excellent performance photodetectors are the goals of continuous pursuit and challenge. 2D material photodetectors have become a research hotspot due to the special propert-ies of 2D materials including flexible tuning, no dangling bonds, high mobility, and many more. Herein, the electronic and optoelectronic properties of 2D materials and the quality factors of the photodetector are introduced. Then, the 2D material-based photodetectors with a detection wavelength from visible light to the terahertz band are summarized systematically. Finally, the prospects and challenges of 2D material-based photodetectors are discussed briefly.