
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 nanoopticsâ€, 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