Nonlinear photoresponse of type-II Weyl semimetals

Abstract

The experimental manifestation of topological effects in bulk materials under ambient conditions, especially those with practical applications, has attracted enormous research interest. Recent discovery of Weyl semimetal provides an ideal material platform for such endeavors. The Berry curvature in a Weyl semimetal becomes singular at the Weyl node, creating an effective magnetic monopole in the k-space. A pair of Weyl nodes carry quantized effective magnetic charges with opposite signs, and therefore, opposite chirality. Although Weyl-point-related signatures such as chiral anomaly and non-closing surface Fermi arcs have been detected through transport and ARPES measurements, direct experimental evidence of the effective k-space monopole of the Weyl nodes has so far been lacking. In this work, signatures of the singular topology in a type-II Weyl semimetal TaIrTe4 is revealed in the photo responses, which are shown to be directly related to the divergence of Berry curvature. As a result of the divergence of Berry curvature at the Weyl nodes, TaIrTe4 exhibits unusually large photo responsivity of 130.2 mA/W with 4-m excitation in an unbiased field effect transistor at room temperature arising from the third-order nonlinear optical response.The room temperature mid-IR responsivity is approaching the performance of commercial HgCdTe detector operating at low temperature, making Type-II Weyl semimetal TaIrTe4 of practical importance in terms of photo sensing and solar energy harvesting. Furthermore, the circularly polarized galvanic response is also enhanced at 4-m, possibly due to the same Berry curvature singularity enhancement as the shift current. Considering the optical selection rule of Weyl cones with opposite chirality, it may open new experimental possibilities for studying and controlling the chiral polarization of Weyl Fermions through an in-plane DC electric field in addition to the optical helicities.

Anisotropic ultrasensitive PdTe 2 -based phototransistor for room-temperature long-wavelength detection

“…5A, the dc electric field E DC introduced by bias voltage can break the symmetrical plane, making the nonequilibrium carriers move laterally along the electric field and the photocurrent generate a linear growth behavior similar to the photoconductive process (35). In addition, applying in-plane E DC has recently been found to provide additional control means for giant shift current, as a result of the production of imbalanced allowed momentum space for optical excitations (21). In this regard, the nonequilibrium carriers localized near the metal-material interface could produce a net nonlinear component of photocurrent proportional to the E DC , in addition to the bias-independent components.…”

PtTe2‐Based Type‐II Dirac Semimetal and Its van der Waals Heterostructure for Sensitive Room Temperature Terahertz Photodetection

“…However, the PtTe 2 ‐based device shows an excellent photoresponsivity even at zero bias. Possible photoresponses can be shifted current response, the photon‐drag effect, photothermoelectric effect, but it is still not clear from the results in this work, which require further investigations. The performance of the detector is demonstrated at room temperature and ambient environment by using 0.12 THz radiation with the power density of 1.05 mW cm −2 .…”

Acoustogalvanic Effect in Dirac and Weyl Semimetals

“…For example, photocurrents of such magnitudes were recently observed in, e.g., Ref. [72]. As an additional advantage over the conventional acoustoelectric effect, which relies on usual electric field, pseudoelectromagnetic fields that drive acoustogalvanic currents are not subject to screening and could, in principle, attain significantly high values.…”