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Quantum Hydrodynamics: Applications to nanoplasmonics

Periodic Reporting for period 1 - QHYDRO (Quantum Hydrodynamics: Applications to nanoplasmonics)

Reporting period: 2016-10-01 to 2018-09-30

Recent years have witnessed a remarkable surge in interest for the electronic properties of new materials, particularly when excited by electromagnetic radiation. This is a very vast domain of research that encompasses all sorts of nano-objects (metallic films and nanoparticles, carbon nanotubes, semiconductor quantum dots,...) new materials like graphene, as well as metamaterials whose structure can be engineered so as to display some particular optical properties. In this project, we will focus our attention on metallic nano-objects and the composite metamaterials that can be constructed out of them, such as networks of interacting nanoparticles.

Standard methods to study the electron response – such as the time-dependent density functional theory or Hartree-Fock equations – are computationally very costly in terms of run time and memory storage. On the other hand, recent approaches rely on much simpler methods based on improvements of the classical Mie theory. Here in this project, we have developed and implemented a set of quantum hydrodynamic (QHD) models that are sufficiently simple to be run on standard computers (desktop PC or small university cluster), but contain enough physics to study the electron response beyond the Mie model – in particular nonlinear, nonlocal, and quantum effects. The combination of flexibility and accuracy of QHD models makes them an ideal tool to investigate many open problems in the emerging field of nanoplasmonics.

Using this approach, several configurations of nano-objects can be studied, including dimers and trimers of metallic nanoparticles and nanorods, metal-dielectric multilayers, nanoparticles in the vicinity of a thin metal film, and arrays of nanoparticles interacting via the dipole force.
"The first 6-8 months of the project were spent mostly on the preliminary training for the background study of the quantum many body systems and the development of the analytical QHD model. We developed the QHD equations for a spherically symmetric system, applicable to hollow spherical molecules or nanoshells, e.g. fullerenes, gold nanoshells, etc. We first used the model for the description of plasmonic oscillations in the C60 fullerenes. C60 fullerenes exhibit collective plasmonic excitations against the positive ion background, associated with the localised surface plasmon (dipole) mode and the monopole plasmon (breathing) mode. These are attractive candidates for spectroscopic studies in understanding fundamental many-body physics. A variational technique was used to solve analytically the QHD model for the case of breathing plasmonic oscillations, revealing a resonantmode near the plasmon frequency (33 eV), slightly redshifted due to spillout effects, and a second mode around 19 eV.

By the end of 9 months of the project, we have acquired these results that were presented in some internal seminars, international workshops, summer school, etc. described below in details:
• Poster presentation: IPCMS days, 21 - 22 November 2016, CNRS-IPCMS, Strasbourg, France
• Poster presentation: EUCOR meeting on Quantum Science and Technology, 30 March 2017, Strasbourg, France
• Oral presentation: PhD students and Postdocs seminars, 2 June 2017, Department of ultrafast Optics and Nanophotonics (DON), CNRS-IPCMS, Strasbourg, France
• Poster presentation: 2nd International summer School in electronic structure Theory: electron correlation in Physics and Chemistry 18 June – 1 July, 2017, Centre Paul Langevin, Aussois (Savoie) France

On the basis of the knowledge acquired during the development of the QHD analytical method and results obtained for the ground state of the breathing mode of C60, the focus of the project was towards the numerical development of the QHD code. For that purpose, we first studied semi-analytically the linear and non-linear response of the C60 molecule. The computed bulk plasmon frequency is redshifted (both in linear and non-linear regimes) with respect to plasmon frequency due to the large spillout of the electron density with respect to the ion density. We further verified our obtained results from the QHD code by first-principles simulations based on a TDDFT approach. A second collective resonance was detected at 19 eV, same as the one observed in the QHD simulations, thus verifying our developed QHD code.

As a typical example, the QHD approach was used here to investigate the ground state and linear response of metallic nanoshells. Detailed comparison with a fully quantum TDDFT code revealed a satisfactory accordance between the two approaches. These results are encouraging for future more realistic studies of large nanoplasmonics structures using QHD.

Results presented (June 2017 – August 2018):

• Invited Seminar: 2 October 2017, Institut für Sensor- und Aktuatorsysteme, Micro and Nanosensors (MNS) Group, Technische Universität Wien, Vienna, Austria
• Oral presentation: Theory Days 2017, 22 – 24 November 2017, Toulouse, France
• Oral presentation: International Conference on Recent Advances on Mathematical and Physical Science [ICRAMPS 2018], Jhangirnagar University, Dhaka, Bangladesh, 27-29 January 2018
• Invited Seminar: 31 January 2018, Department of Physics, Bangladesh University of Engineering & Technology, Bangladesh.
• Invited Seminar: 1 June 2018, Dipartimento di Fisica ""E. Pancini"", Universita di Napoli “Federico II”, Napoli, Italy
• Poster presentation: Plasmonics and Nanophotonics Gordon Research Conference, 8 – 13 July 2018, Maine, USA
• Oral presentation: SPIE Nanoscience + Engineering 2018, 19 – 23 August 2018 San Diego, USA


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Publications:

• F.Tanjia J Hurst, P.-A. Hervieux, and G. Manfredi, “Plasmonic breathing modes in C60 molecules – A quantum hydrodynamic approach”, Phys. Rev. A 98, 043430 (2018)..
• G. Manfredi, P.-A. Hervieux, F. Tanjia, “Quantum hydrodynamics for nanoplasmonics”, Proc. SPIE 10722, 10722 - 10722 – 5 (2018).


Implementation of QHD in nested fullerenes/carbon buckyonions:
We have implemented our QHD method in such systems, specifically in C60@C240 buckyonions. The preliminary simulation results of the bulk plasmonic oscillations in C60@C240 are very promising. We are now preparing an article to be submitted to a journal in near future.

Networking and outreach activities
• As a member of the Marie Curie Alumni association (MCAA), the grant recipient researcher of this project attended the 2017 MCAA Conference and General Assembly was held on Friday 24th and Saturday 25th March 2017 in Salamanca, Spain.
Link: https://www.mariecuriealumni.eu/events/2017-mcaa-conference-and-general-assembly

• The 6th Young Minds Leadership Meeting was held on 12 - 13 May 2017 at the University of Naples Federico II, Naples, Italy. The grant recipient researcher of this project delivered a presentation - “Opportunity and future of a young researcher in Europe: perspective of an outsider”, talking about her own experience as a young research student starting from Bangladesh until her current MSC fellowship in Strasbourg.

Link: http://www.epsnews.eu/2017/06/6th-eps-young-minds-leadership-meeting/

• The researcher was invited to attend the panel discussion – “Career in Academia” at the Joint Conference of the EPS and DPG Condensed Matter Divisions, Berlin, 11-16 March, 2018.
Link: https://www.dpg-verhandlungen.de/year/2018/conference/berlin/part/akjdpg/session/6/contribution/1
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