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Welcome to the Bittner research group at the University of Houston

We use theoretical approaches to answer the following questions:

  • Can we develop novel spectroscopies based upon quantum light.

  • How do we describe quantum phase transitions in optically driven systems.

  • How do these effects affect the observed dynamics, material properties, or electronic behavior in systems such as organic light-emitting diodes, photovoltaic cells, and DNA chains.

Group News

Recent group highlights

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The molecular origin of Frenkel biexciton binding.
Elizabeth Gutiérrez MezaRavyn MalatestaHongmo LiIlaria BargigiaAjay Ram Srimath KandadaDavid A. Valverde-ChávezNatalie StingelinSergei TretiakEric R. BittnerCarlos Silva
Submitted to Science Advances, March 2021
Frenkel excitons are primary photoexcitations in molecular semiconductors and are unequivocally responsible for their optical properties. However, the spectrum of corresponding biexcitons - bound exciton pairs - has not been resolved thus far in organic materials. We correlate the energy of two-quantum exciton resonances with that of the quantum transition by means of nonlinear coherent spectroscopy. Using a Frenkel exciton model, we relate the biexciton binding energy to the magnitude and the sign of the exciton-exciton interaction energy and the inter-site hopping energy, which are molecular parameters that can be quantified by quantum chemistry. Unexpectedly, excitons with interchain vibronic dispersion reveal intrachain biexciton correlations, and vice-versa. The details of biexciton correlations determine exciton bimolecular annihilation, which is ubiquitous in organic semiconductors. It is crucial to quantify these interactions in order to establish a quantum-mechanical basis for their rate constants. Our work enables new opportunities for general insights into the many-body electronic structure in molecular excitonic systems such as organic semiconductor crystals, molecular aggregates, photosynthetic light-harvesting complexes, and DNA.
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Stochastic scattering theory for excitation induced dephasing: Time-dependent nonlinear coherent exciton lineshapes
ARS Kandada, H Li, F Thouin, ER Bittner, C Silva
J. Chem. Phys. 153, 164706 (2020)

We develop a stochastic theory that treats time-dependent exciton–exciton s-wave scattering and that accounts for dynamic Coulomb screening, which we describe within a mean-field limit. With this theory, we model excitation-induced dephasing effects on time-resolved two-dimensional coherent optical lineshapes and we identify a number of features that can be attributed to the many-body dynamics occurring in the background of the exciton, including dynamic line narrowing, mixing of real and imaginary spectral components, and multi-quantum states. We test the model by means of multidimensional coherent spectroscopy on a two-dimensional metal-halide semiconductor that hosts tightly bound excitons and biexcitons that feature strong polaronic character. We find that the exciton nonlinear coherent lineshape reflects many-body correlations that give rise to excitation-induced dephasing. Furthermore, we observe that the exciton lineshape evolves with the population time over time windows in which the population itself is static in a manner that reveals the evolution of the multi-exciton many-body couplings. Specifically, the dephasing dynamics slow down with time, at a rate that is governed by the strength of exciton many-body interactions and on the dynamic Coulomb screening potential. The real part of the coherent optical lineshape displays strong dispersive character at zero time, which transforms to an absorptive lineshape on the dissipation timescale of excitation-induced dephasing effects, while the imaginary part displays converse behavior. Our microscopic theoretical approach is sufficiently flexible to allow for a wide exploration of how system-bath dynamics contribute to linear and non-linear time-resolved spectral behavior.
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Mixed Quantum Classical Simulations of Charge-Transfer Dynamics in a Model Light-Harvesting Complex. I. Charge-Transfer Dynamics,
Kush Patel and Eric R. Bittner*
Cite this: J. Phys. Chem. B 2020, 124, 11, 2149
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Non-equilibrium states of a plasmonic Dicke model with coherent and dissipative surface plasmon-quantum emitter interactions
Andrei Piryatinski, Oleksiy Roslyak, Hao Li, Eric R. Bittner
Phys. Rev. Research. 2, 013141 (2020).