Plasmon Lifetime Research Articles

Fundamental limits to graphene plasmonics.

Plasmon polaritons are hybrid excitations of light and mobile electrons that can confine the energy of long-wavelength radiation at the nanoscale. Plasmon polaritons may enable many enigmatic quantum effects, including lasing 1 , topological protection2,3 and dipole-forbidden absorption 4 . A necessary condition for realizing such phenomena is a long plasmonic lifetime, which is notoriously difficult to achieve for highly confined modes 5 . Plasmon polaritons in graphene-hybrids of Dirac quasiparticles and infrared photons-provide a platform for exploring light-matter interaction at the nanoscale6,7. However, plasmonic dissipation in graphene is substantial 8 and its fundamental limits remain undetermined. Here we use nanometre-scale infrared imaging to investigate propagating plasmon polaritons in high-mobility encapsulated graphene at cryogenic temperatures. In this regime, the propagation of plasmon polaritons is primarily restricted by the dielectric losses of the encapsulated layers, with a minor contribution from electron-phonon interactions. At liquid-nitrogen temperatures, the intrinsic plasmonic propagation length can exceed 10 micrometres, or 50 plasmonic wavelengths, thus setting a record for highly confined and tunable polariton modes. Our nanoscale imaging results reveal the physics of plasmonic dissipation and will be instrumental in mitigating such losses in heterostructure engineering applications.

Surface Plasmon Enhanced Emission From Defects in Gallium Doped ZnO

In this work, the optical properties of defects coupled with surface plasmons (SPs) in gallium‐doped ZnO (ZnO:Ga) grown by molecular beam epitaxy (MBE) have been explored. The photoluminescence intensity is enhanced by up to 4.9 times as a result of SPs coupling by decorating the sample with silver nanospheres (Ag NSs), with a fast plasmonic decay lifetime of 0.1 ns compared with the defect‐assisted carrier recombination lifetime of 3.77 ns in the as‐grown sample. The enhanced emission intensity depends on the plasmonic modes determined by the diameter of Ag NSs, verified by power‐dependent photoluminescence measurements. Confocal mapping reveals that the plasmonic “hot‐spots”, that is, enhanced emission around the Ag NSs, exhibit a highly optical stability with reduced photoluminescence blinking. This work demonstrates that a defect coupled with SPs in ZnO is a promising high‐efficiency emitter for applications in nanophotonics.

Lifetime of surface plasmons

We calculate the lifetime of a surface plasmon on the surface of jellium metal from the process of the surface plasmon decaying into electron-hole pairs in the metal. We find that this process only occurs over a finite interval of wave vector, and at large values of wave vector. Our calculation contained two new features: (i) we used the Brillouin formula to normalize the electromagnetic field traveling along the surface and (ii) we included the spin rotation term in the electron current. The latter contribution has no effect at large wave vector of the surface plasmon.

Plasmonic Horizon in Gold Nanosponges

An electromagnetic wave impinging on a gold nanosponge coherently excites many electromagnetic hot-spots inside the nanosponge, yielding a polarization-dependent scattering spectrum. In contrast, a hole, recombining with an electron, can locally excite plasmonic hot-spots only within a horizon given by the lifetime of localized plasmons and the speed carrying the information that a plasmon has been created. This horizon is about 57 nm, decreasing with increasing size of the nanosponge. Consequently, photoluminescence from large gold nanosponges appears unpolarized.

Plasmon Modulation Spectroscopy of Noble Metals to Reveal the Distribution of the Fermi Surface Electrons in the Conduction Band

To directly access the dynamics of electron distribution near the Fermi-surface after plasmon excitation, pump-probe spectroscopy was performed by pumping plasmons on noble-metal films and probing the interband transition. Spectral change in the interband transitions is sensitive to the electron distribution near the Fermi-surface, because it involves the d valence-band to the conduction band transitions and should reflect the k-space distribution dynamics of electrons. For the continuous-wave pump and probe experiment, the plasmon modulation spectra are found to differ from both the current modulation and temperature difference spectra, possibly reflecting signatures of the plasmon wave function. For the femtosecond-pulse pump and probe experiment, the transient spectra agree well with the known spectra upon the excitation of the respective electrons resulting from plasmon relaxation, probably because the lifetime of plasmons is shorter than the pulse duration.

Long-Lived Domain Wall Plasmons in Gapped Bilayer Graphene.

Topological domain walls in dual-gated gapped bilayer graphene host edge states that are gate-tunable and valley polarized. Here we predict that plasmonic collective modes can propagate along these topological domain walls even at zero bulk density and possess a markedly different character from that of bulk plasmons. Strikingly, domain wall plasmons are extremely long-lived with plasmon lifetimes that can be orders of magnitude larger than the transport scattering time in the bulk at low temperatures. Importantly, long domain wall plasmon lifetimes persist even at room temperature with values up to a few picoseconds. Domain wall plasmons possess a rich phenomenology including plasmon oscillation over a wide range of frequencies (up to the mid-infrared), tunable subwavelength electromagnetic confinement lengths, as well as a valley polarization for forward/backward propagating modes. Its unusual features render them as a new tool for realizing low-dissipation plasmonics that transcend the restrictions of the bulk.

First-principles calculations and model analysis of plasmon excitations in graphene and graphene/hBN heterostructure

Plasmon excitations in free-standing graphene and graphene/hexagonal boron nitride (hBN) heterostructure are studied using linear-response time-dependent density functional theory within the random phase approximation. Within a single theoretical framework, we examine both the plasmon dispersion behavior and lifetime (linewidth) of Dirac and $\ensuremath{\pi}$ plasmons on an equal footing. Particular attention is paid to the influence of the hBN substrate and the anisotropic effect. Furthermore, a model-based analysis indicates that the correct dispersion behavior of $\ensuremath{\pi}$ plasmons should be ${\ensuremath{\omega}}_{\ensuremath{\pi}}(q)=\sqrt{{E}_{g}^{2}+\ensuremath{\beta}q\phantom{{}^{l}}}$ for small $q$'s, where ${E}_{g}$ is the band gap at the $M$ point in the Brillouin zone, and $\ensuremath{\beta}$ is a fitting parameter. This model is radically different from previous proposals, but in good agreement with our calculated results from first principles.

Plasmon-assisted resonant tunneling in graphene-based heterostructures

We develop a theory of electron tunneling accompanied by carrier-carrier scattering in graphene - insulator - graphene heterostructures. Due to the dynamic screening of Coulomb interaction, the scattering-aided tunneling is resonantly enhanced if the transferred energy and momentum correspond to those of surface plasmons. We reveal the possible experimental manifestations of such plasmon-assisted tunneling in current-voltage curves and plasmon emission spectra of graphene-based tunnel junctions. We find that inelastic current and plasmon emission rates have sharp peaks at voltages providing equal energies, momenta and group velocities of plasmons and interlayer single-particle excitations. The strength of this resonance, which we call plasmaronic resonance, is limited by interlayer twist and plasmon lifetime. The onset of plasmon-assisted tunneling can be also marked by a cusp in the junction $I(V)$-curve at low temperatures, and the threshold voltage for such tunneling weakly depends on carrier density and persists in the presence of interlayer twist.

Gain-modulated plasmonic Rabi oscillations of coupled nanocomplex

Strong coupling in nanostructures can bring intriguing optical phenomena such as ultrafast Rabi oscillation—periodical energy exchange phenomenon between two modes. Rabi splitting appears in the frequency-domain spectra for strong coupling system. However, in metallic nanosystems the time-domain Rabi oscillations are hard to be observed because the plasmon lifetime is limited by the heavy ohmic losses. Here we report a theoretical investigation of surface plasmon coupling behaviour of two gold nanorods with one being a core-shell rod filled with a gain material and find the periodic energy exchange phenomenon which recalls the concept of Rabi oscillation. The gain material-cored gold-shell structure dipolar mode hybridizes with the solid gold rod quadrupolar mode to form the Fano resonances. Energy exchange between the two rods happens through the near field coupling. Two approaches, to prolong plasmon lifetime by increasing the gain efficiency and to increase Rabi oscillation frequency by increasing the coupling strength, are suggested to increase the Rabi oscillation cycles. Our results offer a way to achieve unique control of light at the nanoscale and further to explore plasmonic Rabi oscillation phenomena in plasmonic nanosystems.

Infrared Nanophotonics Based on Graphene Plasmonics

Graphene plasmonics has recently attracted remarkable attention, with reports of numerous intriguing properties and novel device demonstrations. As a two-dimensional (2-D) semimetal with ultrahigh carrier mobility, graphene can host plasmon waves that exhibit extremely tight spatial confinement, exceptionally long plasmon lifetime, and an electrostatically tunable response in the mid-infrared (mid-IR) and terahertz (THz). These properties render graphene a viable plasmonic material for achieving novel functionalities in various mid-IR to THz photonic systems. From the device perspective, we review the key distinguishing features of graphene plasmons and highlight the latest developments, such as mid-IR and THz tunable infrared sources, modulators, and photodetectors. Finally, we discuss future challenges and new opportunities for graphene plasmonics in infrared photonic systems.

Molecular Vibration Induced Plasmon Decay

Noble metal nanoparticles, when interacting with an external electric field, give rise to a phenomenon called surface plasmon resonance characterized by collective valence electron oscillations, and because of this unique feature, these systems are employed for a large and heterogeneous number of applications. To improve their performance, it is necessary to develop a deep knowledge of the main factors affecting the plasmon lifetime. In order to answer this question, in this work a linear silver chain is investigated as a simplified model for silver nanorods. Through a nonadiabatic molecular dynamics approach the role of nuclear dynamics on transverse plasmon lifetime is investigated. A strong dependence of plasmon dynamics on the specific nature of nuclear motions is found: nuclear motions along the chain do not affect the transverse plasmon lifetime while motions causing a deviation from linearity of the wire have an important impact on the plasmon dynamics causing its decay. As the vibrational energy i...

Plasmon assisted control of photo-induced excitation energy transfer in a molecular chain

The strong and ultrafast laser pulse excitation of a molecular chain in close vicinity to a spherical metal nano-particle (MNP) is studied theoretically. Due to local-field enhancement around the MNP, pronounced excited-state formation has to be expected for the part of the chain which is in proximity to the MNP. Here, the description of this phenomenon will be based on a uniform quantum theory of the MNP–molecule system. It accounts for local-field effects due to direct consideration of the strong excitation energy transfer coupling between the MNP and the various molecules. The molecule–MNP distances are chosen in such a way as to achieve a correct description of the MNP via dipole–plasmon excitations. Short plasmon life-times are incorporated in the framework of a density matrix approach. By extending earlier work the present description allows for multi-exciton formation and multiple dipole–plasmon excitation. The region of less intense and not-too-short optical excitation is identified as being best suited for excitation energy localization in the chain.

Measurements of the femtosecond relaxation dynamics of Tamm plasmon-polaritons

This paper reports on measurements of the lifetime of Tamm plasmon-polaritons (TPPs) excited in a 1D photonic-crystal/thin-metal-film structure. A femtosecond pulse reflected from a structure of this kind is found to be significantly distorted if its spectrum overlaps with the Tamm plasmon resonance. It is shown that the TPP lifetime possesses strong polarization and angular dependence. It varies from 20 fs for p-polarized light to 40 fs for s-polarized light at a 45° angle of incidence. The reported lifetime of Tamm plasmons is several times smaller than the previously reported lifetime of surface plasmons.

Visible quantum plasmonics from metallic nanodimers

We report theoretical evidence that bulk nonlinear materials weakly interacting with highly localized plasmonic modes in ultra-sub-wavelength metallic nanostructures can lead to nonlinear effects at the single plasmon level in the visible range. In particular, the two-plasmon interaction energy in such systems is numerically estimated to be comparable with the typical plasmon linewidths. Localized surface plasmons are thus predicted to exhibit a purely nonclassical behavior, which can be clearly identified by a sub-Poissonian second-order correlation in the signal scattered from the quantized plasmonic field under coherent electromagnetic excitation. We explicitly show that systems sensitive to single-plasmon scattering can be experimentally realized by combining electromagnetic confinement in the interstitial region of gold nanodimers with local infiltration or deposition of ordinary nonlinear materials. We also propose configurations that could allow to realistically detect such an effect with state-of-the-art technology, overcoming the limitations imposed by the short plasmonic lifetime.

Surface plasmon lifetime in metal nanoshells

The lifetime of localized surface plasmon plays an important role in many aspects of plasmonics and its applications. In small metal nanostructures, the dominant mechanism restricting plasmon lifetime is size-dependent Landau damping. We performed quantum-mechanical calculations of Landau damping for the bright surface plasmon mode in a metal nanoshell. In contrast to the conventional model based on the electron surface scattering, we found that the damping rate decreases as the nanoshell thickness is reduced. The origin of this behavior is traced to the spatial distribution of plasmon local field inside the metal shell. We also found that, due to interference of electron scattering amplitudes from nanoshell's two metal surfaces, the damping rate exhibits pronounced quantum beats with changing shell thickness.

Ultrafast Dynamics of Plasmon-Exciton Interaction of Ag Nanowire- Graphene Hybrids for Surface Catalytic Reactions.

Using the ultrafast pump-probe transient absorption spectroscopy, the femtosecond-resolved plasmon-exciton interaction of graphene-Ag nanowire hybrids is experimentally investigated, in the VIS-NIR region. The plasmonic lifetime of Ag nanowire is about 150 ± 7 femtosecond (fs). For a single layer of graphene, the fast dynamic process at 275 ± 77 fs is due to the excitation of graphene excitons, and the slow process at 1.4 ± 0.3 picosecond (ps) is due to the plasmonic hot electron interaction with phonons of graphene. For the graphene-Ag nanowire hybrids, the time scale of the plasmon-induced hot electron transferring to graphene is 534 ± 108 fs, and the metal plasmon enhanced graphene plasmon is about 3.2 ± 0.8 ps in the VIS region. The graphene-Ag nanowire hybrids can be used for plasmon-driven chemical reactions. This graphene-mediated surface-enhanced Raman scattering substrate significantly increases the probability and efficiency of surface catalytic reactions co-driven by graphene-Ag nanowire hybridization, in comparison with reactions individually driven by monolayer graphene or single Ag nanowire. This implies that the graphene-Ag nanowire hybrids can not only lead to a significant accumulation of high-density hot electrons, but also significantly increase the plasmon-to-electron conversion efficiency, due to strong plasmon-exciton coupling.

High-Energy Surface and Volume Plasmons in Nanopatterned Sub-10 nm Aluminum Nanostructures.

In this work, we use electron energy-loss spectroscopy to map the complete plasmonic spectrum of aluminum nanodisks with diameters ranging from 3 to 120 nm fabricated by high-resolution electron-beam lithography. Our nanopatterning approach allows us to produce localized surface plasmon resonances across a wide spectral range spanning 2-8 eV. Electromagnetic simulations using the finite element method support the existence of dipolar, quadrupolar, and hexapolar surface plasmon modes as well as centrosymmetric breathing modes depending on the location of the electron-beam excitation. In addition, we have developed an approach using nanolithography that is capable of meV control over the energy and attosecond control over the lifetime of volume plasmons in these nanodisks. The precise measurement of volume plasmon lifetime may also provide an opportunity to probe and control the DC electrical conductivity of highly confined metallic nanostructures. Lastly, we show the strong influence of the nanodisk boundary in determining both the energy and lifetime of surface plasmons and volume plasmons locally across individual aluminum nanodisks, and we have compared these observations to similar effects produced by scaling the nanodisk diameter.

Tailoring Plasmon Lifetime in Suspended Nanoantenna Arrays for High-Performance Plasmon Sensing

We demonstrate significantly longer plasmon lifetime and stronger electric field enhancement by lifting the nanoantenna arrays above the substrate by dielectric nanopillars. The role of the pillar is to offer a more homogeneous dielectric background allowing stronger diffraction coupling among plasmonic nanoantennas leading to a Fanolike asymmetric lineshape. It is found that the electric fields around the nanoantennas can be greatly enhanced when the Fanolike resonance is excited, and a 4.2 times enhancement is achieved compared with the pure resonance in individual nanoantennas. Furthermore, only a collective surface mode with its electric fields of the same direction as the induced electric moment in the nanoantennas could mediate the excitation of such a Fanolike resonance. More importantly, the sensitivity and the figure of merit (FOM) of this plasmonic structure can reach as high as 900 nm/RIU and 53, respectively. Our study offers a new, simple, and efficient way to design the plasmonic systems with desired electric field enhancement and spectral lineshape for different applications.

Far-Field Spectroscopy and Near-Field Optical Imaging of Coupled Plasmon-Phonon Polaritons in 2D van der Waals Heterostructures.

A new hybridized plasmon-phonon polariton mode in graphene/h-BN van der Waals heterostructures is presented, featuring the ultrahigh field confinement characteristic of the graphene plasmon and the long lifetime property of the h-BN transverse optical phonon. This enables an ultralong hybrid plasmon lifetime of up to 1.6 ps (with ultrahigh mode confinement up to >l0(2)/7000 and ultrasmall group velocity down to 0.001c, where c is the speed of light in vacuum), superior to any localized plasmon ever demonstrated.

Extending the plasmonic lifetime of tip-enhanced Raman spectroscopy probes

Tip-enhanced Raman spectroscopy (TERS) is an emerging technique for simultaneous mapping of chemical composition and topography of a surface at the nanoscale. However, rapid degradation of TERS probes, especially those coated with silver, is a major bottleneck to the widespread uptake of this technique and severely prohibits the success of many TERS experiments. In this work, we carry out a systematic time-series study of the plasmonic degradation of Ag-coated TERS probes under different environmental conditions and demonstrate that a low oxygen (<1 ppm) and a low moisture (<1 ppm) environment can significantly improve the plasmonic lifetime of TERS probes from a few hours to a few months. Furthermore, using X-ray photoelectron spectroscopy (XPS) measurements on Ag nanoparticles we show that the rapid plasmonic degradation of Ag-coated TERS probes can be correlated to surface oxide formation. Finally, we present practical guidelines for the effective use and storage of TERS probes to improve their plasmonic lifetime based on the results of this study.