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

Our optimal implementation of time-dependent density functional theory within linear response allows computing the optical properties of systems with several thousands of atoms [1,2].

We applied this method to study the dependence of the near-field enhancement and localization on the structural details of the plasmonic nano-gaps [3,4], the different size dispersion of the plasmon resonance of silver and sodium nanoparticles and how this behaviour correlates with the presence of 4d electrons in the Ag case [2], and more recently to describe valence EELS [5].

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. [6] 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 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 conductance quantization in metal nanocontacts, small 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.

The author acknowledges financial support from FP7 FET-ICT project No. 610446 project, MINECO (Grant No. MAT2013-46593-C6-2-P), the Basque Dep. de Educación and the UPV/EHU (Grant No. IT-756-13).

References

[1] P. Koval, et al., J. Phys.: Cond. Matter 28, (2016) 214001
[2] M. Barbry, N. E. Koval, J. Aizpurua, D. Sánchez-Portal and P. Koval, submitted
[3] M. Barbry, et al., Nano Letters 354, (2015) 216
[4] M. Urbieta, et al., ACS Nano 12, (2018) 585-595
[5] M. Barbry, P. Koval and D. Sánchez-Portal, in preparation (2018)
[6] F. Marchesin, et al., ACS Photonics 3, (2016) 269-277