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Register a new userNonlinear optical response of a local surface plasmon coupled to a 2D material
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We present a theoretical study of the optical response of a nonlinear oscillator formed by coupling a metal nanoparticle local surface plasmon resonance to excitonic degrees of freedom in a monolayer transition-metal dichalcogenide. We show that the combined system should exhibit strong anharmonicity in its low-lying states, predicting for example a seven order-of-magnitude increase in nonlinearity relative to a silicon photonic crystal cavity. Then, we demonstrate that such system exhibits strong quantum features such as antibunching and non-Gaussianity. Arrays of such nanoscale nonlinear oscillators could be used to realize novel optical metamaterials; alternatively, an individual nanoparticle-monolayer construct could be coupled to an optical resonator to mediate efficient input-output coupling to propagating fields.
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Graphene is a rising star in nonlinear optics due to its saturable absorption and giant Kerr nonlinearity, these properties are useful in digital optics based on optical nonlinear devices. However, practical applications require large optical nonlinearities and these are inherently limited by the interaction length of atomically thin graphene. Here, we demonstrate optical bistability in a Fabry Perot cavity containing monolayer and bilayer graphene which have been restructured to form nanobubbles. We find that graphene nanobubble can act as a new type of optical nonlinear media due to its vertical side wall as well as added curvature, which enable strong non linear dispersive effects leading to a large optically induced phase change. Unlike thermally induced bistability, the all optical switching between two transmission states happens within a time scale of tens of nanoseconds. Nanobubble based optical devices with intrinsic optical nonlinearity help to overcome the optical path length limitation of atomically thin two dimensional films and allow us to explore the promise of using such elements as the building block of digital all-optical circuitry.
Quantum geometric tensor (QGT), including a symmetric real part defined as quantum metric and an antisymmetric part defined as Berry curvature, is essential for understanding many phenomena. We studied the photogalvanic effect of a multiple-band system with time-reversal-invariant symmetry by theoretical analysis in this work. We concluded that the integral of gradient of the symmetric part of QGT in momentum space is related to the linearly photogalvanic effect, while the integral of gradient of Berry curvature is related to the circularly photogalvanic effect. Our work afforded an alternative interpretation for the photogalvanic effect in the view of QGT, and a simple approach to detect the QGT by nonlinear optical response.
We performed ultrafast degenerate pump-probe spectroscopy on monolayer WSe2 near its exciton resonance. The observed differential reflectance signals exhibit signatures of strong many-body interactions including the exciton-exciton interaction and free carrier induced band gap renormalization. The exciton-exciton interaction results in a resonance blue shift which lasts for the exciton lifetime (several ps), while the band gap renormalization manifests as a resonance red shift with several tens ps lifetime. Our model based on the many-body interactions for the nonlinear optical susceptibility fits well the experimental observations. The power dependence of the spectra shows that with the increase of pump power, the exciton population increases linearly and then saturates, while the free carrier density increases superlinearly, implying that exciton Auger recombination could be the origin of these free carriers. Our model demonstrates a simple but efficient method for quantitatively analyzing the spectra, and indicates the important role of Coulomb interactions in nonlinear optical responses of such 2D materials.
Thin nanomaterials are key constituents of modern quantum technologies and materials research. Identifying specimens of these materials with properties required for the development of state of the art quantum devices is usually a complex and lengthy human task. In this work we provide a neural-network driven solution that allows for accurate and efficient scanning, data-processing and sample identification of experimentally relevant two-dimensional materials. We show how to approach classification of imperfect imbalanced data sets using an iterative application of multiple noisy neural networks. We embed the trained classifier into a comprehensive solution for end-to-end automatized data processing and sample identification.
Noble metal nanostructures are ubiquitous elements in nano-optics, supporting plasmon modes that can focus light down to length scales commensurate with nonlocal effects associated with quantum confinement and spatial dispersion in the underlying electron gas. Nonlocal effects are naturally more prominent for crystalline noble metals, which potentially offer lower intrinsic loss than their amorphous counterparts, and with particular crystal facets giving rise to distinct electronic surface states. Here, we employ a quantum-mechanical model to describe nonclassical effects impacting the optical response of crystalline noble-metal films and demonstrate that these can be well-captured using a set of surface-response functions known as Feibelman $d$-parameters. In particular, we characterize the $d$-parameters associated with the (111) and (100) crystal facets of gold, silver, and copper, emphasizing the importance of surface effects arising due to electron wave function spill-out and the surface-projected band gap emerging from atomic-layer corrugation. We then show that the extracted $d$-parameters can be straightforwardly applied to describe the optical response of various nanoscale metal morphologies of interest, including metallic ultra-thin films, graphene-metal heterostructures hosting extremely confined acoustic graphene plasmons, and crystallographic faceted metallic nanoparticles supporting localized surface plasmons. The tabulated $d$-parameters reported here can circumvent computationally expensive first-principles atomistic simulations to describe microscopic nonlocal effects in the optical response of mesoscopic crystalline metal surfaces, which are becoming widely available with increasing control over morphology down to atomic length scales for state-of-the-art experiments in nano-optics.
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