Two emerging material classes, namely, two-dimensional transition-metal carbides and nitrides (MXenes) and Weyl Semimetals (WSMs) offer exciting opportunities for tailorable photonic devices. The designer-like characteristics of MXenes, achievable with the choice of composition, stoichiometry and surface termination, and tunable properties of single crystalline WSMs, realized through the manipulation of surface conditions, lead to impressive tunability of optical properties in both systems. MXenes exhibit diverse optical properties ranging from plasmonic behavior to dielectric-to-metallic transition as well as strong nonlinear response useful for ultrafast applications. In turn, WSMs such as TaAs show high photocurrent generation and strong second-harmonic generation while WTe2 holds a promise for chiral anomaly applications. The manipulation of linear and nonlinear optical response including the epsilon near zero (ENZ) behavior as well as investigation of hybrid plasmonic-MXene and plasmonic-WSM structures open a broad range of applications for these materials in emerging photonics.
Weyl semimetals (WSMs) is an emerging class of materials possessing unique electromagnetic properties that are not commonly achievable with conventional metals and semiconductors. The exotic phenomena emerging from the so-called Weyl nodes in WSMs where valence and conduction bands cross in single points and electrons effectively behave as Weyl fermions make WSMs very interesting for novel photonic applications in areas of non-linear optics, photovoltaics, THz electrooptics, and detection. In this work, we explore the enhancement of WSM nonlinear response by merging WSMs with the concept of plasmonics, i.e. nano-optics utilizing deeply subwavelength collective oscillations of free electrons in metallic nanostructures, and metasurfaces where arrays of plasmonic nanoantennas are used to control the phase, amplitude and polarization of the incident light. Since electrons possess non-trivial electronic states in WSMs, plasmonics could enable the observation of unique optoelectrical phenomena in WSMs with the added benefit of creating nonlinear optical elements that are smaller than the diffraction limit. Here, we realized a nanopatch plasmonic antenna array on the WSM TaAs crystal to demonstrate the enhanced non-linear optical response from TaAs. By developing a large-scale, non-destructive method of fabricating the antenna array, we address the challenge of WSM integration with photonic devices. We demonstrate a six-fold increase of the second-harmonic generation (SHG) from the Weyl semimetal TaAs surface by distributing plasmonic silver nanoantennas on TaAs.
We experimentally demonstrate light modulation of near-infrared beam at wavelength 1550 nm by near-visible light at wavelength 810 nm with a mean number of photons less than 1 per pulse using an avalanche photodiode.
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