Weyl semimetals are gapless topological states of matter [1][2][3][4][5][6][7][8][9][10][11][12] with broken inversion and/or time reversal symmetry, which can support unconventional responses to externally applied electrical, optical and magnetic fields. Here we report a new photogalvanic effect in type-II WSMs, MoTe2 and Mo0.9W0.1Te2, which are observed to support a circulating photocurrent when illuminated by circularly polarized light at normal incidence. This effect occurs exclusively in the inversion broken phase, where crucially we find that it is associated with a spatially varying

A bolometer is a device that makes an electrical resistive response to the electromagnetic radiation resulted from a raise of temperature due to heating. The combination of the extremely weak electron-phonon interactions along with its small electron heat capacity makes graphene an ideal material for applications in ultra-fast and sensitive hot electron bolometer. However, a major issue is that the resistance of pristine graphene weakly depends on the electronic temperature. We propose using disordered graphene to obtain a strongly temperature dependent resistance. The measured electrical responsivity of the disordered graphene bolometer reaches 6 × 106 V/W at 1.5 K, corresponding to an optical responsivity of 1.6 × 105 V/W. The deduced electrical noise equivalent power is 1.2 , corresponding to the optical noise equivalent power of 44 . The minimal device structure and no requirement for high mobility graphene make a step forward towards the applications of graphene hot electron bolometers.

We study exciton-plasmon coupling in two-dimensional semiconductors coupled with Ag plasmonic lattices via angle-resolved reflectance spectroscopy and by solving the equations of motion (EOMs) in a coupled oscillator model accounting for all the resonances of the system. Five resonances are considered in the EOM model: semiconductor A and B excitons, localized surface plasmon resonances (LSPRs) of plasmonic nanostructures and the lattice diffraction modes of the plasmonic array. We investigated the exciton-plasmon coupling in different 2D semiconductors and plasmonic lattice geometries, including monolayer MoS2 and 2 WS2 coupled with Ag nanodisk and bowtie arrays, and examined the dispersion and lineshape evolution in the coupled systems via the EOM model with different exciton-plasmon coupling parameters. The EOM approach provides a unified description of the exciton-plasmon interaction in the weak, intermediate and strong coupling cases with correctly explaining the dispersion and lineshapes of the complex system. This study provides a much deeper understanding of lightmatter interactions in multilevel systems in general and will be useful to instruct the design of novel two-dimensional exciton-plasmonic devices for a variety of optoelectronic applications with precisely tailored responses. Keywords: 2D semiconductor, exciton plasmon, polariton, Purcell enhancement, Fano resonance, MoS2, WS2 Study of light-matter interactions is essential in understanding and manipulating the optical properties of materials to enable new and unprecedented functionalities. When light interacts with matter, in particularly, a direct bandgap semiconductor, absorption of a photon leads to the formation of a coupled electron-hole pair (excitons) bonded via coulombic interaction. The exciton can then recombine radiatively and emit a photon, allowing energy transfer back and forth between the photon and the exciton. Depending on the relative magnitudes between such energy transfer rate (coupling strength, ), and the dissipation rate, of each state, the system can be broadly classified into three light-matter coupling regimes 1 : (1) weak coupling regime, where the coupling strength ≪ − , with and representing the decay rate of the excitonic and 3 photonic states, respectively. In this regime, the eigenstates of the coupled system remain unchanged from their initial uncoupled states, and the system can be described by a perturbation theory where the Purcell effect 2 , i.e., the modification of the spontaneous emission rate via engineering the photon density of states, can be observed. Purcell effect has been extensively studied for enhancing and suppressing the spontaneous emission rate in various cavity geometries 3-4 , with applications in photonic and plasmonic lasers 5-6 , brighter single-photon sources 7-8 , hot luminescence 9-10 and quantum cryptography 11 . (2) intermediate coupling regime with − < < + , in which normal mode splitting occurs in the frequency domain, and an anti-crossing behavior generally observed in the far-fie...

Two-dimensional semiconductors host excitons with very large oscillator strengthsand binding energies due to significantly reduced carrier screening. Two-dimensional semiconductors integrated with optical cavities are emerging as a promising platform for studying strong light-matter interactions as a route to explore a variety of exotic many-body effects. Here, in few-layered WS2 coupled with plasmonic nanoparticle lattices, we observe the formation of a collective polaritonic mode near the exciton energy and the formation of

Germanium telluride (GeTe) is both polar and metallic, an unusual combination of properties in any material system. The large concentration of free-carriers in GeTe precludes the coupling of external electric field with internal polarization, rendering it ineffective for conventional ferroelectric applications and polarization switching. Here we investigate alternate ways of coupling the polar domains in GeTe to external electrical stimuli through optical second harmonic generation polarimetry and in situ TEM electrical testing on single-crystalline GeTe nanowires. We show that anti-phase boundaries, created from current pulses (heat shocks), invert the polarization of selective domains resulting in reorganization of certain 71o domain boundaries into 109o boundaries. These boundaries subsequently interact and evolve with the partial dislocations, which migrate from domain to domain with the carrier-wind force (electrical current). This work suggests that current pulses and carrier-wind force could be external stimuli for domain engineering in ferroelectrics with significant current leakage.

Dynamic control of nonlinear signals is critical for a wide variety of optoelectronic applications, such as signal processing for optical computing. However, controlling nonlinear optical signals with large modulation strengths and near-perfect contrast remains a challenging problem due to intrinsic second-order nonlinear coefficients via bulk or surface contributions. Here, via electrical control, we turn on and tune second-order nonlinear coefficients in semiconducting CdS nanobelts from zero to up to 151 pm V−1, a value higher than other intrinsic nonlinear coefficients in CdS. We also observe ultrahigh ON/OFF ratio of >104 and modulation strengths ~200% V−1 of the nonlinear signal. The unusual nonlinear behavior, including super-quadratic voltage and power dependence, is ascribed to the high-field domain, which can be further controlled by near-infrared optical excitation and electrical gating. The ability to electrically control nonlinear optical signals in nanostructures can enable optoelectronic devices such as optical transistors and modulators for on-chip integrated photonics.

Previous studies of electron-phonon interaction in impure graphene have found that static disorder can give rise to an enhancement of electronic cooling. We investigate the effect of dynamic disorder and observe over an order of magnitude suppression of electronic cooling compared with clean graphene. The effect is stronger in graphene with more vacancies, confirming its vacancyinduced nature. The dependence of the coupling constant on the phonon temperature implies its link to the dynamics of disorder. Our study highlights the effect of disorder on electron-phonon interaction in graphene. In addition, the suppression of electronic cooling holds great promise for improving the performance of graphene-based bolometer and photo-detector devices.

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