Dafei Jin

Terahertz plasmonics in ferroelectric-gated graphene

Inspired by recent advancement of ferroelectric-gated memories and transistors, we propose a design of ferroelectric-gated nanoplasmonic devices based on graphene sheets clamped in ferroelectric crystals. We show that the two-dimensional plasmons in graphene can strongly couple with the phonon-polaritons in ferroelectrics, leading to characteristic modal wavelength of the order of 100–200 nm at low temperature and low-THz frequencies albeit with an appreciable dissipation. By patterning the ferroelectrics into different domains, one can produce compact on-chip plasmonic waveguides, which exhibit negligible crosstalk even at 20 nm separation distance. Harnessing the memory effect of ferroelectrics, low-power operation can be achieved on these plasmonic waveguides.

Infrared Topological Plasmons in Graphene

We propose a two-dimensional plasmonic platform-periodically patterned monolayer graphene-which hosts topological one-way edge states operable up to infrared frequencies. We classify the band topology of this plasmonic system under time-reversal-symmetry breaking induced by a static magnetic field. At finite doping, the system supports topologically nontrivial band gaps with mid-gap frequencies up to tens of terahertz. By the bulk-edge correspondence, these band gaps host topologically protected one-way edge plasmons, which are immune to backscattering from structural defects and subject only to intrinsic material and radiation loss. Our findings reveal a promising approach to engineer topologically robust chiral plasmonic devices and demonstrate a realistic example of high-frequency topological edge states.

Quantum-Spillover-Enhanced Surface-Plasmonic Absorption at the Interface of Silver and High-Index Dielectrics

We demonstrate an unexpectedly strong surface-plasmonic absorption at the interface of silver and high-index dielectrics based on electron and photon spectroscopy. The measured bandwidth and intensity of absorption deviate significantly from the classical theory. Our density-functional calculation well predicts the occurrence of this phenomenon. It reveals that due to the low metal-to-dielectric work function at such interfaces, conduction electrons can display a drastic quantum spillover, causing the interfacial electron-hole pair production to dominate the decay of surface plasmons. This finding can be of fundamental importance in understanding and designing quantum nanoplasmonic devices that utilize noble metals and high-index dielectrics.

Optical torque from enhanced scattering by multipolar plasmonic resonance

Abstract We present a theoretical study of the optical angular momentum transfer from a circularly polarized plane wave to thin metal nanoparticles of different rotational symmetries. While absorption has been regarded as the predominant mechanism of torque generation on the nanoscale, we demonstrate numerically how the contribution from scattering can be enhanced by using multipolar plasmon resonance. The multipolar modes in non-circular particles can convert the angular momentum carried by the scattered field and thereby produce scattering-dominant optical torque, while a circularly symmetric particle cannot. Our results show that the optical torque induced by resonant scattering can contribute to 80% of the total optical torque in gold particles. This scattering-dominant torque generation is extremely mode-specific, and deserves to be distinguished from the absorption-dominant mechanism. Our findings might have applications in optical manipulation on the nanoscale as well as new designs in plasmonics and metamaterials.

Ultrafast fluorescent decay induced by metal-mediated dipole–dipole interaction in two-dimensional molecular aggregates

Significance Quantitative understanding of the ultrafast energy transfer between fluorescent nanoemitters and the environment is essential in nanophotonics and optoelectronics and beneficial to many industrial applications. For nanoemitters like single or colloidal dye molecules or quantum dots, their fluorescence decay near a metallic substrate can be described by a noninteracting single-dipole picture. In this work, we find a dominant fluorescent decay channel in a 2D molecular aggregate as a result of the strong and coherent dipole–dipole interaction mediated by a metallic substrate. This unique mechanism leads to an ultrafast fluorescent decay and 10-times greater energy dissipation rate than expected. Our finding opens up a unique way to manipulate energy transfer and to develop light-energy devices on the molecular level. Two-dimensional molecular aggregate (2DMA), a thin sheet of strongly interacting dipole molecules self-assembled at close distance on an ordered lattice, is a fascinating fluorescent material. It is distinctively different from the conventional (single or colloidal) dye molecules and quantum dots. In this paper, we verify that when a 2DMA is placed at a nanometric distance from a metallic substrate, the strong and coherent interaction between the dipoles inside the 2DMA dominates its fluorescent decay at a picosecond timescale. Our streak-camera lifetime measurement and interacting lattice–dipole calculation reveal that the metal-mediated dipole–dipole interaction shortens the fluorescent lifetime to about one-half and increases the energy dissipation rate by 10 times that expected from the noninteracting single-dipole picture. Our finding can enrich our understanding of nanoscale energy transfer in molecular excitonic systems and may designate a unique direction for developing fast and efficient optoelectronic devices.

High-precision broadband measurement of refractive index by picosecond real-time interferometry

The refractive index is one of the most important quantities that characterize a materials optical properties. However, it is hard to measure this value over a wide range of wavelengths. Here, we demonstrate a new technique to achieve a spectrally broad refractive index measurement. When a broadband pulse passes through a sample, different wavelengths experience different delays. By comparing the delayed pulse to a reference pulse, the zero path difference position for each wavelength can be obtained and the materials dispersion can be retrieved. Our technique is highly robust and accurate, and can be miniaturized in a straightforward manner.

Publisher’s Note: Infrared Topological Plasmons in Graphene [Phys. Rev. Lett. 118 , 245301 (2017)]

This corrects the article DOI: 10.1103/PhysRevLett.118.245301.

STEM-EELS Study of Plasmonic Modes in Ag nanotriangles: Size and Dielectric Dependence

In this work, we study the quality factor of each surface plasmonic mode excited on Ag nanotriangles which is the measure of materials acceptibilty for plasmonics based devices. Present work is focus on triangular shaped Ag nanoparticles, which have a high quality factor and a simple geometry to ease the understanding the complicated physics of plasmonic excitations [3]. In addition, the LSPR modes in Ag lies in the visible and infrared light range which makes in compelling candidate for the development of highly sensitive photonic and phononic biosensors [4].

Quest for an Optical Circuit Probe

What is common in near field optics and the electronic circuit probe techniques? Typical electronic test probes are conveniently used to connect test equipment such as oscilloscopes to an RF integrated circuit. Likewise in near field optics, it is highly desirable if we have similar precision test probes with both high spatial and spectral resolution to study the optical phenomena. Such light-matter interaction in nanostructures involving single and collective emitters can enhance our understanding and design for cavity quantum electrodynamics.

Quantum Electromechanical Processes in Plasmonic Nanostructures

Summary form only given. We present analysis of electromechanical effects associated with collective optical excitation of electrons in plasmonic nanoparticles, with emphasis on the enhanced transfer of angular momentum and nonlinear hydrodynamics such as vortex pairs.