arXiv subjects

Ilaria Bargigia

Publications and source records attributed to Ilaria Bargigia.

6 recordsLinked to original sources

arXiv2022

Identifying incoherent mixing effects in the coherent two-dimensional photocurrent excitation spectra of semiconductors

We have previously demonstrated that in the context of two-dimensional (2D) coherent electronic spectroscopy measured by phase modulation and phase-sensitive detection, an \emph{incoherent} nonlinear response, due to pairs of photoexcitations produced via linear excitation pathways, contribute to the measured signal as unexpected background [Grégoire et al., J.\ Chem.\ Phys. \textbf{147}, 114201 (2017)]. Here, we simulate the effect of such incoherent population mixing in the photocurrent signal collected from a GaAs solar cell by acting externally on the transimpedance amplifier circuit used for phase-sensitive detection, and we identify an effective strategy to recognize the presence of incoherent population mixing in 2D data. While we find that incoherent mixing is reflected by cross-talk between the linear amplitude at the two time-delay variables in the four-pulse excitation sequence, we do not observe any strict phase correlations between the coherent and incoherent contributions, as expected from modelling of a simple system.

cond-mat.mtrl-sci↗

arXiv2021

Frenkel biexcitons in hybrid HJ photophysical aggregates

Frenkel excitons, the primary photoexcitations in organic semiconductors that are unequivocally responsible for the optical properties of this materials class, are predicted to form \emph{bound} exciton pairs, i.e., biexcitons. These are key intermediates, ubiquitous in many relevant photophysical processes; for example, they determine the exciton bimolecular annihilation dynamics in such systems. Deciphering the details of biexciton correlations is, thus, of utmost importance to understand the optical processes in these semiconductors. To date, however, due to their spectral ambiguity, there has been only scant direct evidence of bound biexcitons, limiting the insights that can be gained. Moreover, a quantum-mechanical basis describing biexciton correlation/stability has so far been lacking. By employing nonlinear coherent spectroscopy, we identify here bound biexcitons in a model polymeric semiconductor. We find, unexpectedly, that excitons with \emph{interchain} vibronic dispersion reveal \emph{intrachain} biexciton correlations and vice versa. Moreover, using a Frenkel exciton model, we can relate the biexciton binding energy to molecular parameters quantified by quantum chemistry, including the magnitude and sign of the exciton-exciton interaction the inter-site hopping energies. Therefore, our work promises a window towards general insights into the many-body electronic structure in polymeric semiconductors and beyond; e.g., other excitonic systems such as organic semiconductor crystals, molecular aggregates, photosynthetic light-harvesting complexes, or DNA.

cond-mat.mtrl-sci↗

arXiv2019

Intrinsically distinct hole and electron transport in conjugated polymers controlled by intra and intermolecular interactions

It is still a matter of controversy whether the relative difference in hole and electron transport in solution-processed organic semiconductors is either due to intrinsic properties linked to chemical and solid-state structure or to extrinsic factors, as device architecture. We here isolate the intrinsic factors affecting either electron or hole transport within the same film microstructure of a model copolymer semiconductor. Relatively, holes predominantly bleach inter-chain interactions with H-type electronic coupling character, while electrons' relaxation more strongly involves intra-chain interactions with J-type character. Holes and electrons mobility correlates with the presence of a charge transfer state, while their ratio is a function of the relative content of intra- and inter-molecular interactions. Such fundamental observation, revealing the specific role of the ground-state intra- and inter-molecular coupling in selectively assisting charge transport, allows predicting a more favorable hole or electron transport already from screening the polymer film ground state optical properties.

physics.chem-ph↗

arXiv2019

Quantum process tomography of entangled photons as a probe of intermediates of singlet fission in a tetracene derivative

Spin-entaglement has been proposed and extensively used in the case of correlated triplet pairs which are intermediate states in singlet fission process in select organic semiconductors. Here, we employ quantum process tomography of polarization entangled photon-pairs resonant with the excited state absorption of these states to investigate the nature of the inherent quantum correlations and to explore for an unambiguous proof for the existence of exciton entanglement.

physics.chem-ph↗

arXiv2019

Electron-phonon couplings inherent in polarons drive exciton dynamics in two-dimensional metal-halide perovskites

We report on the exciton formation and relaxation dynamics following photocarrier injection in a single-layer two-dimensional lead-iodide perovskite. We probe the time evolution of four distinct exciton resonances by means of time-resolved photoluminescence and transient absorption spectroscopies, and find that at 5\,K a subset of excitons form on a $\lesssim$ 1-ps timescale, and that these relax subsequently to lower-energy excitons on $\sim$ 5--10\,ps with a marked temperature dependence over $<$ 100\,K. We implement a mode projection analysis that determines the relative contribution of all observed phonons with frequency $\leq$50\,cm$^{-1}$ to inter-exciton nonadiabatic coupling, which in turn determines the rate of exciton relaxation. This analysis ranks the relative contribution of the phonons that participate in polaronic lattice distortions to the exciton inter-conversion dynamics and thus establishes their role in the nonadiabatic mixing of exciton states, and this in the exciton relaxation rate.

cond-mat.mtrl-sci↗

arXiv2019

Phonon coherences reveal the polaronic character of excitons in two-dimensional lead-halide perovskites

Hybrid organic-inorganic semiconductors feature complex lattice dynamics due to the ionic character of the crystal and the softness arising from non-covalent bonds between molecular moieties and the inorganic network. Here we establish that such dynamic structural complexity in a prototypical two-dimensional lead iodide perovskite gives rise to the coexistence of diverse excitonic resonances, each with a distinct degree of polaronic character. By means of high-resolution resonant impulsive stimulated Raman spectroscopy, we identify vibrational wavepacket dynamics that evolve along different configurational coordinates for distinct excitons and photocarriers. Employing density functional theory calculations, we assign the observed coherent vibrational modes to various low-frequency ($\lesssim 50$\,cm$^{-1}$) optical phonons involving motion in the lead-iodide layers. We thus conclude that different excitons induce specific lattice reorganizations, which are signatures of polaronic binding. This insight on the energetic/configurational landscape involving globally neutral primary photoexcitations may be relevant to a broader class of emerging hybrid semiconductor materials.

cond-mat.mtrl-sci↗