Conference Agenda

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Session Overview
S-2: Exciton and polariton spectroscopy 1
Monday, 08/Jul/2019:
11:10 - 12:20

Session Chair: Malte Gather
Location: Main Hall
"Artis Centrum Hotel" (Address: Totoriu str. 23, Vilnius, LT-01120, Lithuania)

11:10 - 11:35
ID: 265
Oral presentation


Stephane Kena-Cohen

Polytechnique Montreal, Montreal, Canada

We will first describe our recent work on time-resolved imaging of carrier diffusion in halide perovskite thin films. We will highlight a number of surprising effects which have been observed, such as non-diffusive transport in long-lifetime film compositions as well as important caveats to previous measurements of diffusion constants and recombination coefficients. We will then describe experiments where we have created microcavities in the ultrastrong light-matter coupling regime that allow for a full inversion of the singlet polariton and triplet states in a thermally-assisted delayed fluorescence material. We will explain the conditions under which such reversals can affect reverse intersystem crossing. Finally, we will describe our recent observations of room-temperature superfluidity in organic microcavities as well as strong polariton-polariton nonlinearities in microcavities that use monolayers of transition metal dichalcogenides as the active layer.

11:35 - 11:50
ID: 130
Oral presentation


Eric Bittner

University of Houston, Houston, United States of America

Recent advances in both theory and experimental technique have advanced the notion that there might be something to be gained by probing material systems with quantum photons, as opposed to more conventional laser sources. First, I shall discuss a couple of recent experiments that demonstrate that one can, in fact, extract ultrafast (fs) time-scale dynamics using CW sources and our theoretical methods for computing such responses. I shall propose that exciton/exciton correlations lead to the production of entangled photons being emitted from a sample system. By measuring the entanglement entropy, one has a direct measure of both the magnitude and time-scale of such correlations.

11:50 - 12:05
ID: 189
Oral presentation


Cristina Sissa, Anna Painelli, Swathi K.

Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, Italy

The translation of chirality from the molecular level to supramolecular aggregates and materials is a key phenomenon in chemistry, material science, biology, etc., and the mechanisms that govern the trasmisssion of chirality across different length scales deserve attention. Here we present different theoretical approaches to describe the (chiro)optical behavior of supramolecular aggregates and plasmonic structures in the UV-Vis region.

The exciton model is adopted to investigate the optical behaviour of supramolecular aggregates, where intermolecular interactions are estimated using the dipolar approximation. The focus of the work is on the role of interactions between non-degenerate excitons, and their influence on chiroptical properties. Calculated UV-Vis and CD spectra are compared with experimental data of supramolecular assemblies of phenyleneethynylene molecules (experimental data are provided by the group of Prof. K. G. Thomas, IISER-Thiruvananthapuram, India), substituted with chiral groups as to form chiral aggregates. The proposed theoretical approach offers the opportunity to investigate the origin of the complex chiroptical behavior (non-bisignated signals) observed in these aggregates. [Kar, S.; Swathi, K.; Sissa, C.; Painelli, A.; Thomas, K. G., J. Phys. Chem. Lett. 2018, 4584-4590]

The model proposed by Govorov [Fan, Z.; Govorov, A. O. Nano Lett. 2010, 10, 2580-2587] for the chiroptical response of nanoplasmonic aggregates is adopted to rationalize the electronic CD spectra of chiral plasmonic structures. The two different theoretical approaches adopted for supramolecular aggregates and plasmonic structures allows to appreciate the different nature of interactions responsible for (chiro)optical properties. For molecular aggregates, the electric field generated by each molecule on surrounding molecules negligibly affects the molecular properties. On the opposite, in plasmonic aggregates the local electric field is large and has important effects, particularly when the distance between adjacent NPs becomes comparable to the NP diameter.

12:05 - 12:20
ID: 121
Oral presentation


Max Marcus, George Knee, Animesh Datta

University of Warwick, Coventry, United Kingdom

We present a simple and unambiguous way to determine the presence of quantum coherences in excitonic energt transport (EET) using two-pulse pump-probe spectroscopy. The theoretical framework of process tomography, readily known within Quantum Information Theory, allows for the estimation of the importance of quantum effects in any process, here in particular EET. However, full quantum process tomorgraphy is expensive and liable to error. We present a simplified approach which acts as a quantum witness, making it possible to determine the presence of quantum effects (in particular coherences) within exciton migration in multichromophoric systems. While conceptually trivial for de-coupled excitons (qubits), the extension to strongly correlated exciton-phonon systems have been published recently [G. C. Knee, M. Marcus, L. D. Smith, A. Datta, Phys Rev A 122, 052328 (2018)] and we present numerical results on model dimer systems. The strength of our approach lies within its simplicity, only utilising pump-probe experimental set ups, and its umabiguity in determining the presence of quantum coherences in the eigenbasis of the measurement. The extension to a larger number of sites, in order so simulate more realistic systems showing EET, such as the FMO complex, is currently in development and preliminary results may be available in time for the conference.