Probing the ultimate plasmon confinement limits with a Van der Waals heterostructure

Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary MaterialsThe ability to confine light into tiny spatial dimensions is important for applications such as microscopy, sensing and nanoscale lasers. While plasmons offer an appealing avenue to confine light, Landau damping in metals imposes a trade-off between optical field confinement and losses. We show that a graphene-insulator-metal heterostructure can overcome that trade-off, and demonstrate plasmon confinement down to the ultimate limit of the lengthscale of one atom. This is achieved by far-field excitation of plasmon modes squeezed into an atomically thin hexagonal boron nitride dielectric h-BN spacer between graphene and metal rods. A theoretical model which takes into account the non-local optical response of both graphene and metal is used to describe the results. These ultra-confined plasmonic modes, addressed with far-field light excitation, enables a route to new regimes of ultra-strong light-matter interactions.The authors thank Gerasimos Konstantatos and Valerio Pruneri for the intensive use of their respective FTIRs, very insightful discussions with Marco Polini, Thomas Christensen, Asger Mortenson and Javier Aizpurua on non-local effects and with Achim Woessner on simulation and modelling of graphene acoustic plasmonsmodes. Funding: We acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0522), support by Fundacio Cellex Barcelona, the Mineco grants Ramon y Cajal (RYC-2012-12281), Plan Nacional (FIS201347161-P and FIS2014-59639-JIN), and the Government of Catalonia trough the SGR grant (2014-SGR-1535). Furthermore, the research leading to these results has received funding from the European Union H2020 Programme under grant agreement no. 604391 Graphene Flagship, the ERC starting grant (307806, CarbonLight) and project GRASP (FP7-ICT-2013613024-GRASP).D.A.I.acknowledges the FPI gran tBES-2014-068504. N.M.R.P.andE.J.C.D acknowledge support from the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Financing UID/FIS/04650/2013. This work was supported in part by the Center for Excitonics, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award No. de-sc0001088, and the Army Research Office (grant number 16112776). J.-Y.H. and J.K. acknowledge support from the USA FOSRFATEMURI, GrantNo. FA9550-15-1-0514. Author contributions: F.H.L.K, D.A.I. and S.N. conceived the idea; E.J.C.D and N.M.R.P. developed the analytical model; S.N., C.P., J.O.,D.E. and D.A.I. fabricated the devices; S.N., R.P.and D.A.I.performed measurements; D.A.I., M.L., I.E., and S.N. performed data analysis; J.Y.H. and J.K. provided h-BN; D.A.I., S.N., E.J.C.D., N.M.R.P, I.E., D.E. and F.H.L.K wrote the manuscript; D.E. and F.K. supervised the project. Competing interests: None of the authors have competing interests.info:eu-repo/semantics/publishedVersio

Structure de bandes et transport électronique dans les nanotubes de carbone sous champ magnétique intense

Electronic transport measurements in individual multiwall carbon nanotubes under pulsed magnetic field (60T) are presented in this PhD thesis. The purpose is to observe modulations of the electronic dispersion by the magnetic field. High quality nanotubes are contacted with short distances between contacts. This allows to reach quasi-ballistic and slightly diffusive transport regimes occurring mainly on the outer wall. Transistor configuration enables to modulate the charge carrier energy (Fermi level) through many subbands by an electrostatic potential (“a gate”). In order to clarify the contribution of innermore shells, a spectroscopic Raman study is first presented. A strong variation from wall to wall of the intensity of charge transfer between successive shells is unraveled. The study under magnetic field of nanotubes with semiconducting and metallic outer wall is then presented. When the magnetic field is applied perpendicularly to the axis of the nanotube, the onset of propagating Landau states is unveiled. This induces modulations of resonance conditions in an electronic Fabry-Pérot type regime, closing of the energy gap in a semiconducting shell and reintroduction of backscattering in a metallic one. This last effect comes with a pinning of the Fermi level to the Landau one gathering at zero energy under high field. Those results are in agreement with theoretical models taking into account an homogeneous disorder. Finally, the Aharonov-Bohm effect under many periods and many subbands is observed when the field is parallel to the axis of the nanotube. The metallicity of the outer wall and the correspondence between the gate voltage and the charge carrier energy are obtained by comparing the experimental conductance oscillations with a model obtained in the perfect case. To describe further the magneto-fingerprints, transmission lowering at the contacts and due to defects are qualitatively considered.Des mesures de transport électronique dans des nanotubes de carbone multiparois individuels sous champ magnétique pulsé (60T) sont présentées dans cette thèse. L'objectif est d'observer les modifications de la dispersion électronique par le champ magnétique. Des nanotubes de très bonne qualité cristalline sont connectés sur des distances courtes entre contacts, permettant d'atteindre des régimes de transport quasi-balistiques ou faiblement diffusifs, la paroi externe contribuant principalement. La configuration transistor permet de moduler l'énergie des porteurs (niveau de Fermi) sur plusieurs sous-bandes via un potentiel électrostatique (dit de grille). Afin de préciser la contribution des parois plus internes, une étude en spectroscopie Raman est présentée dans un premier temps. Nous constatons que l'intensité du transfert de charges entre parois successives varie fortement d'un feuillet à l'autre. L'étude sous champ magnétiques de nanotubes de parois externes semiconductrices et métalliques est ensuite présentée. Lorsque le champ magnétique est appliqué perpendiculairement à l'axe du nanotube, la formation de niveaux de Landau propagatifs est mise en évidence. Celle-ci se traduit par des modulations des conditions de résonance dans un régime de type Fabry-Pérot électronique, par la fermeture du gap électronique d'une paroi semiconductrice ainsi que la réintroduction de la rétrodiffusion dans une paroi métallique. Ce dernier effet s'accompagne d'un ancrage du niveau de Fermi vers celui de Landau se formant à énergie nulle à très fort champ. L'ensemble de ces résultats est en accord avec des modèles théoriques prenant en compte un désordre homogène. Enfin, l'effet Aharonov-Bohm sur plusieurs périodes et plusieurs sous-bandes est observé sous un champ parallèle à l'axe du nanotube. La métallicité de la paroi externe et la correspondance entre la tension de grille et l'énergie des porteurs sont obtenues en comparant les oscillations de conductance expérimentales à un modèle obtenu pour un cas parfait. Afin de décrire en détail la signature magnétique, les diminutions des transmissions aux contacts et la contribution de défauts sont qualitativement étudiées

Exploring the electronic band structure of individual carbon nanotubes under 60 T.

International audienc

Doping dependence of the G-band Raman spectra of an individual multiwall carbon nanotube

International audienc