VILLUM Investigator program on Quantum Plasmonics
Dr. techn. N. Asger Mortensen
Professor & VILLUM Investigator
D-IAS Chair of Technical Science
My current curriosity-driven fundamental research in quantum plasmonics is supported by the recently awarded VILLUM Investigator program, which is a personal 40 MDKK grant [~5.3 MEUR] awarded by the VILLUM Foundation. I am also supported by the Independent Research Fund Denmark, while the research on 2D materials is partly supported by the Danish National Research Foundation through my affiliation with the CNG Center of Excellence for Nanostructured Graphene.
For more information on the VILLUM Investigator grant, see the official announcement.
From classical to quantum plasmonics
Plasmons are the collective oscillations of free electrons in conducting media, such as metals, but also doped semiconductors and graphene-like two-dimensional materials. The science and technology of plasmons is known as plasmonics. Plasmons can be observed in bulk materials, but they can also be excited in tiny nanostructures, e.g., by interactions with light. While the interaction of light (electromagnetic waves) with matter is commonly treated classically, we have a cuririosity for situations where classical electrodynamics is interfacing regimes with quantum physics.
S.I. Bozhevolnyi & N.A. Mortensen, “Plasmonics for emerging quantum technologies",
A.I. Fernández-Domínguez, S.I. Bozhevolnyi & N.A. Mortensen, "Plasmon-enhanced generation of non-classical light", ACS Photonics 5, 3447 (2018).
Historically, the field of plasmonics has developed with a solid foundation in classical electrodynamics employing semi-classical descriptions of the interactions of light with matter. In particular, the collective oscillation of conduction electrons subject to driving optical fields has been conceptually analyzed within Drude theory and the local-response approximation, where the material response occurs only in the point of space of the perturbation, while there is no response at even short distances. In our work on nonlocal response we have developed theoretical formalism to account for the finite compressibility of the quantum electron gas, quantum spill-out, as well as for the Landau damping associated with electron-hole pair excitations.
N.A. Mortensen et al., “A generalized non-local optical response in nanoplasmonics”,
G. Toscano et al., “Resonance shifts and spill-out effects in self-consistent hydrodynamic nanoplasmonics”, Nature Commun. 6, 7132 (2015).
W. Yan et al., "Projected Dipole Model for Quantum Plasmonics", Phys. Rev. Lett. 115, 137403 (2015).
T. Christensen et al., “Quantum corrections in nanoplasmonics: shape, scale, and material”,
M.K. Dezfouli et al., “Nonlocal quasinormal modes for arbitrarily shaped three-dimensional plasmonic resonators”, Optica 4, 1503 (2017).
Plasmons are charge-density waves, that can be excited by time-varying electrical fields associated with either impinging photons or electrons. Both type of waves have a diffraction limit, that will eventually place fundamental limits on the spatial resolution by which we may explore plasmons. However, utilizing highly energetic electrons (several kilo-electronvolts), we have used electron microscopy to resolve plasmons in ultra small metallic nanostructures with almost atomic-scale resolution.
S. Raza et al., ”Extremely confined gap surface plasmon modes excited by electrons”,
S. Raza et al., ”Multipole plasmons and their disappearance in few-nanometre silver nanoparticles”,
S. Raza et al., “Electron energy-loss spectroscopy of branched gap plasmon resonators”, Nature Commun. 7, 13790 (2016).
2D photonic materials
Plasmons can also be hosted by one-atom thin sheets of materials, such as graphene, while semiconducting 2D materials also host excitons. Given the tunability and tight confinement of charge carriers, 2D materials are also natural candidates for explorations of quantum-plasmonic phenomena and they may also host strong coupling phenomena, e.g. when excitons hybridize with plasmons supported by nearby metallic nanostructures.
S. Yan et al., “Slow-light-enhanced energy efficiency for the graphene microheater on silicon photonic crystal waveguides”, Nature Commun. 8, 14411 (2017).
M.N. Gjerding et al., “Layered van der Waals crystals with hyperbolic light dispersion”,
P.A.D. Gonçalves et al., “Universal description of channel plasmons in 2D materials”, Optica 4, 595 (2017).
Plasmonic colors are structural colors that emerge from resonant interactions between light and metallic nanostructures. Plasmonic color nanotechnology based on localized surface plasmon resonances, such as gap plasmons and hybridized disk–hole plasmons, allows for color printing with sub-diffraction resolution. Beyond the more fundamental interests, plasmonic colors can be used to color large surfaces, can be mass-produced and dynamically reconfigured, and can provide sub-diffraction resolution with implications for high-density information storage.
J.S. Clausen et al.,
“Plasmonic metasurfaces for coloration of plastic consumer products”,
X. Zhu et al.,
"Plasmonic colour laser printing”,
A. Kristensen et al.,
”Plasmonic colour generation”,
X. Zhu et al.,
“Resonant laser printing of structural colors on high-index dielectric metasurfaces”,