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Insights into nanoplasmonics from first-principles time-dependent density functional simulations

Monday, February 12, 2018 - 11:00
nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
Daniel Sanchez-Portal, Centro de Física de Materiales CSIC-UPV/EHU and DIPC, Donostia, Spain
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In this talk I will present a summary of our recent efforts to describe the plasmonic response of nanostructures using time-dependent density functional theory in the linear response formulation. Our codes [1] use an efficient iterative algorithm that allows computing the optical response of systems containing up to several thousands of atoms [2,3]. 
Using this method we have studied several problems in nanoplasmonics like the dependence of the near-field enhancement and localization on the details of the structure of the plasmonic gaps. In particular, we found that in presence of atomic features at the surfaces of the nanoparticles the electromagnetic field localizes down to atomic-scale dimensions showing large resonant (plasmonic) and non-resonant (lightning rod effect) field enhancements [4,5]. We have also reproduced the different size dispersion of the plasmon resonance of silver and sodium nanoparticles and correlate the different behavior with the screening coming from the 4d electrons in the Ag case [3]. We have also modified our method to describe valence EELS in nanostructures [6]. 
However, in this talk I will concentrate mostly in the correlation between transport properties across sub-nanometric metallic gaps and the optical response of the system. In Ref. [7] we presented a study of the simultaneous evolution of the structure and the optical response of a plasmonic junction as the particles forming the cavity, two Na380 clusters, approach and retract. Atomic reorganizations are responsible for a large hysteresis of the plasmonic response of the system, which shows a jump-to-contact instability during the approach process and the formation of an atom-sized neck across the junction during retraction. Our calculations show that, due to the quantization of the conductance in metal nanocontacts, atomic-scale reconfigurations play a crucial role in determining the optical response. We observe abrupt changes in the intensity and spectral position of the plasmon resonances, and find a one-to-one correspondence between these jumps and those of the quantized transport as the neck cross-section diminishes. These results point out to a connection between transport and optics at the atomic scale at the frontier of current optoelectronics. 
[1] P. Koval, et al., -Optical response of silver clusters and their hollow shells from Linear-Response TDDFT-, J. Phys.: Cond. Matter 28, 214001 (2016) [2] A. Manjavacas, F. Marchesin, et al., -Tunable Molecular Plasmons in Polycyclic Aromatic Hydrocarbons-, ACS Nano 7, 3635-3643 (2013)  [3] M. Barbry, N. E. Koval, J. Aizpurua, D. Sánchez-Portal and P. Koval, -Size dipersion of the plasmon frequency in metal clusters: ab initio atomistic description-, submitted (2018)  [4] M. Barbry, et al., “Atomistic near-field nanoplasmonics: reaching atomic-scale resolution in nanooptics”, Nano Letters 354, 216 (2015) [5] M. Urbieta, et al., -Atomic-Scale Lightning Rod Effect in Plasmonic Picocavities: A Classical View to a Quantum Effect-, ACS Nano 12, 585-595 (2018) [6] M. Barbry, P. Koval and D. Sánchez-Portal, - An efficient atomistic ab initio implementation of Electron Energy Loss Spectroscopy-, in preparation (2018)  [7] F. Marchesin, et al.,-Plasmonic Response of Metallic Nanojunctions Driven by Single Atom Motion: Quantum Transport Revealed in Optics- ACS Photonics 3, 269-277 (2016)

Host: E. Artacho

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