Ultraefficient Coupling of a Quantum Emitter to the Tunable Guided Plasmons of a Carbon Nanotube

Broadband plasmonic indium arsenide photonic antennas

An on-chip integrated mid-infrared Fabry-Perot (F-P) polariton resonator exhibits excellent biosensing, thermal emission, and quantum laser utility potential. However, the narrow optical response range and absence of optoelectronic tunability have hindered the development of a F-P phonon polariton resonator. The discovery of surface plasmons in semiconductor nanowires provides a novel route to F-P polariton resonator devices with a broadband optical response and multi-field tunability. Due to their high electron mobility and crystalline quality, InAs twinning superlattice (TSL) nanowires have become a promising candidate in plasmonic electronics. We systemically studied the F-P plasmonic resonance of individual InAs TSL nanowires with a scattering-type near-field optical microscope. Using a metallic AFM tip to excite surface plasmons, we can observe odd-order and even-order modes of F-P polariton resonance, breaking the symmetric selection rules. Through nano Fourier transform infrared spectroscopy, we found that InAs nanowires' F-P polariton resonances appear in a broadband frequency range (650-1100 cm^-1) and calculated that the corresponding Q factor is 5-10. This semiconductor F-P polariton resonator with inherent electrical tunability will be essential in integrated nanophotonic circuits.

Gate-tunable plasmons in mixed-dimensional van der Waals heterostructures

Surface plasmons, collective electromagnetic excitations coupled to conduction electron oscillations, enable the manipulation of light-matter interactions at the nanoscale. Plasmon dispersion of metallic structures depends sensitively on their dimensionality and has been intensively studied for fundamental physics as well as applied technologies. Here, we report possible evidence for gate-tunable hybrid plasmons from the dimensionally mixed coupling between one-dimensional (1D) carbon nanotubes and two-dimensional (2D) graphene. In contrast to the carrier density-independent 1D Luttinger liquid plasmons in bare metallic carbon nanotubes, plasmon wavelengths in the 1D-2D heterostructure are modulated by 75% via electrostatic gating while retaining the high figures of merit of 1D plasmons. We propose a theoretical model to describe the electromagnetic interaction between plasmons in nanotubes and graphene, suggesting plasmon hybridization as a possible origin for the observed large plasmon modulation. The mixed-dimensional plasmonic heterostructures may enable diverse designs of tunable plasmonic nanodevices.

Metallic Carbon Nanotube Nanocavities as Ultracompact and Low-loss Fabry-Perot Plasmonic Resonators

Plasmonic resonators enable deep subwavelength manipulation of light matter interactions and have been intensively studied both in fundamental physics as well as for potential technological applications. While various metallic nanostructures have been proposed as plasmonic resonators, their performances are rather limited at mid- and far-infrared wavelengths. Recently, highly confined and low-loss Luttinger liquid plasmons in metallic single-walled carbon nanotubes (SWNTs) have been observed at infrared wavelengths. Here, we tailor metallic SWNTs into ultraclean nanocavities by advanced scanning probe lithography and investigate plasmon modes in these individual nanocavities by infrared nanoimaging. The dependence of mode evolutions on cavity length and excitation wavelength can be captured by a Fabry-Perot resonator model of a plasmon nanowaveguide terminated by highly reflective ends. Plasmonic resonators based on SWNT nanocavities approach the ultimate plasmon confinement limit and open the door to the strong light-matter coupling regime, which may enable various nanophotonic applications.

Quasichiral Interactions between Quantum Emitters at the Nanoscale

We present a combined classical and quantum electrodynamics description of the coupling between two circularly polarized quantum emitters held above a metal surface supporting surface plasmons. Depending on their position and their natural frequency, the emitter-emitter interactions evolve from being reciprocal to nonreciprocal, which makes the system a highly tunable platform for chiral coupling at the nanoscale. By relaxing the stringent material and geometrical constraints for chirality, we explore the interplay between coherent and dissipative coupling mechanisms in the system. Thus, we reveal a quasichiral regime in which its quantum optical properties are governed by its subradiant state, giving rise to extremely sharp spectral features and strong photon correlations.

Plasmonic resonance of distorted graphene nano-ribbon analyzed by boundary element method

Surface plasmon resonances (SPRs) of graphene nano-ribbons (GNRs) have great application potentials in sensing, wave-front control and wave absorbing. However, as a flexible material, graphene is often observed with corrugations in the fabrication and transfer processes. Here the scattering properties of a distorted GNR with a bending ridge are studied by the boundary element method (BEM). It is found that, compared with the flat GNRs, the resonant wavelengths are red-shifted, and the resonant intensity of the 1st order mode is decreased, while that of the higher order modes are increased dramatically for the distorted GNRs. Particularly, due to the appearance of the ridge, both odd modes and even modes are able to be stimulated under tilted incidence. In addition, as the ridge increases, the resonances corresponding to various order modes change in different ways. Applying the spring oscillator theoretical model, these results are explained by the blocking effect of the ridge on the motions of electrons. This work is anticipated to help to understand the physical mechanisms of plasmonic resonances of curved GNRs and distorted structures.

Nanomaterial-Based Plasmon-Enhanced Infrared Spectroscopy

Surface-enhanced infrared absorption (SEIRA) has attracted increasing attention due to the potential of infrared spectroscopy in applications such as molecular trace sensing of solids, polymers, and proteins, specifically fueled by recent substantial developments in infrared plasmonic materials and engineered nanostructures. Here, the significant progress achieved in the past decades is reviewed, along with the current state of the art of SEIRA. In particular, the plasmonic properties of a variety of nanomaterials are discussed (e.g., metals, semiconductors, and graphene) along with their use in the design of efficient SEIRA configurations. To conclude, perspectives on potential applications, including single-molecule detection and in vivo bioassays, are presented.

Surface plasmon polariton amplification in a single-walled carbon nanotube

The interaction of a surface plasmon polariton wave of the far-infrared regime propagating in a single-walled carbon nanotube with a drift current is theoretically investigated. It is shown that under the synchronism condition a surface plasmon polariton amplification mechanism is implemented due to the transfer of electromagnetic energy from a drift current wave into a terahertz surface wave propagating along the surface of a single-walled carbon nanotube. Numerical calculations show that for a typical carbon nanotube surface plasmon polariton amplification coefficient reaches huge values of the order of 10⁶ сm^-1, which makes it possible to create a carbon-nanotube-based spaser.

Dynamic spontaneous emission control of an optical emitter coupled to plasmons in strained graphene

Spontaneous emission control of an optical emitter is critical for many applications, such as in the fields of sensing, integrated photonics and quantum optics. Integrating optical emitters with a mechanical system can provide an avenue for strain sensors as well. Here, the dynamic spontaneous emission modification of an emitter coupled to graphene by uniaxial strain is demonstrated. Our results show that the emission rate can be controlled by tuning the strain of graphene, which depends on the polarized orientation of the emitter. More specifically, the decay rate can be enhanced for several times if the emitter is polarized perpendicular to graphene under strain. Azimuthal angle dependent oscillation of decay rate exists for the emitter polarized parallel to the graphene. Moreover, the controllable decay of the emitter comes from the anisotropic plasmons excitation in strained graphene, which is verified by the corresponding isofrequency contours of plasmons. The strain engineering provides a new platform for dynamic spontaneous emission modulation of emitters coupled with graphene, which opens up intriguing possibilities for the design of strain sensors and quantum devices.

Strong and Broadly Tunable Plasmon Resonances in Thick Films of Aligned Carbon Nanotubes

Low-dimensional plasmonic materials can function as high quality terahertz and infrared antennas at deep subwavelength scales. Despite these antennas' strong coupling to electromagnetic fields, there is a pressing need to further strengthen their absorption. We address this problem by fabricating thick films of aligned, uniformly sized semiconducting carbon nanotubes and showing that their plasmon resonances are strong, narrow, and broadly tunable. With thicknesses ranging from 25 to 250 nm, our films exhibit peak attenuation reaching 70%, ensemble quality factors reaching 9, and electrostatically tunable peak frequencies by a factor of 2.3. Excellent nanotube alignment leads to the attenuation being 99% linearly polarized along the nanotube axis. Increasing the film thickness blueshifts the plasmon resonators down to peak wavelengths as low as 1.4 μm, a new near-infrared regime in which they can both overlap the S₁₁ nanotube exciton energy and access the technologically important infrared telecom band.

Coherent Plasmon and Phonon-Plasmon Resonances in Carbon Nanotubes

Carbon nanotubes provide a rare access point into the plasmon physics of one-dimensional electronic systems. By assembling purified nanotubes into uniformly sized arrays, we show that they support coherent plasmon resonances, that these plasmons couple to nanotube and substrate phonons, and that the resulting phonon-plasmon resonances have quality factors as high as 10. Because nanotube plasmons intensely strengthen electromagnetic fields and light-matter interactions, they provide a compelling platform for surface-enhanced spectroscopy and tunable optical devices at deep-subwavelength scales.

Dynamically tunable plasmonically induced transparency in sinusoidally curved and planar graphene layers

To achieve plasmonically induced transparency (PIT), general near-field plasmonic systems based on couplings between localized plasmon resonances of nanostructures rely heavily on the well-designed interantenna separations. However, the implementation of such devices and techniques encounters great difficulties mainly to due to very small sized dimensions of the nanostructures and gaps between them. Here, we propose and numerically demonstrate that PIT can be achieved by using two graphene layers that are composed of a upper sinusoidally curved layer and a lower planar layer, avoiding any pattern of the graphene sheets. Both the analytical fitting and the Akaike Information Criterion (AIC) method are employed efficiently to distinguish the induced window, which is found to be more likely caused by Autler-Townes splitting (ATS) instead of electromagnetically induced transparency (EIT). Besides, our results show that the resonant modes cannot only be tuned dramatically by geometrically changing the grating amplitude and the interlayer spacing, but also by dynamically varying the Fermi energy of the graphene sheets. Potential applications of the proposed system could be expected on various photonic functional devices, including optical switches, plasmonic sensors.