Coherence in ultrafast processes: from single molecule to plasmonic nanostructures

Emanuele Coccia
Dept. Chemical Sciences, University of Padova, Via Marzolo 1, 35131, Padova, Italy
Mercredi 13 Juin 2018, 11h00
bibliothèque LCT, tour 12 - 13, 4^ème étage

Revealing possible long-living quantum coherence in ultrafast processes allows detecting genuine quantum mechanical effects in complex systems, such as materials [1] and biomolecules [2]. To investigate such effects from a quantum chemistry perspective, we have developed methods to simulate the time evolution of molecular systems based on ab initio calculations that include the effect of an external medium (e.g., a solvent, plasmonic nanoparticles) on the molecule [3], as well as of dephasing of the electronic wave function. The latter has been accomplished by means of the stochastic Schröger equation [4]. To test the approach, we have simulated [5] femtosecond pulse-shaping ultrafast spectroscopy of terrylenediimide[6], finding that the experimental results could be reproduced. Then, we have investigated the absorption of light pulses for a more complex system (a molecular chromophore close to a spherical silver nanoparticle), and we found that including dephasing is essential to provide a qualitatively correct picture of metal-enhanced molecular absorption, that depends on the interplay of light pulse duration, plasmon lifetime and molecular dephasing time [7]. Moreover, preliminary results on possible plasmon-enhanced high-harmonic generation are shown.
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References :
[1] M. E Flatté and I. Tifrea, Manipulating Quantum Coherence in Solid State Systems, Springer (2007); S. Hayashi et al. Sci. Rep. 2014, 4, 4456.
[2] G. D. Scholes J. Phys. Chem. Lett. 2010, 1, 2; E. Collini Chem. Soc. Rev. 2013, 42, 4942.
[3] S. Pipolo and S. Corni J. Phys. Chem. C 2016, 120, 28774.
[4] R. Biele and R. D'Agosta J. Phys.: Condens. Matter 2012, 24, 273201.
[5] E. Coccia, F. Troiani, and S. Corni J. Chem. Phys. 2018, 148, 204112.
[6] R. Hildner, D. Brinks, and N. F. van Hulst Nature Phys. 2011, 7, 172.
[7] E. Coccia and S. Corni, in preparation.