Showing papers by "Ajay Ram Srimath Kandada published in 2019"
TL;DR: High-resolution resonant impulsive stimulated Raman spectroscopy in two-dimensional hybrid metal halide perovskites provides evidence for polaronic effects on excitons, which couple to distinct low-frequency vibrational modes of the ionic lattice.
Abstract: 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 (≲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 into the energetic/configurational landscape involving globally neutral primary photoexcitations may be relevant to a broader class of emerging hybrid semiconductor materials. High-resolution resonant impulsive stimulated Raman spectroscopy in two-dimensional hybrid metal halide perovskites provides evidence for polaronic effects on excitons, which couple to distinct low-frequency vibrational modes of the ionic lattice.
234 citations
TL;DR: In this article, the exciton formation and relaxation dynamics following photocarrier injection in a single-layer two-dimensional lead-iodide perovskite were investigated, and the time evolution of four distinct ex...
Abstract: 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 ex...
35 citations
TL;DR: The structure contains both highly distorted and near-ideal PbI6 octahedra, consistent with the observation of two 207Pb NMR resonances, while the optical properties resemble those of other 2D perovskites with distorted PbThe structure and optical properties of the first 3 × 3 corrugated 2D organic-Pb/Iperovskite are described.
Abstract: (4NPEA)2PbI4 (4NPEA = 4-nitrophenylethylammonium) is the first 3 × 3 corrugated 2D organic-Pb/I perovskite. The nitro groups are involved in cation–cation and cation-iodide interactions. The structure contains both highly distorted and near-ideal PbI6 octahedra, consistent with the observation of two 207Pb NMR resonances, while the optical properties resemble those of other 2D perovskites with distorted PbI6 octahedra.
34 citations
04 Dec 2019
TL;DR: In this article, the consequences of polaronic protection effects in many-body interactions involving excitons and phonon states were explored in two-dimensional perovskites.
Abstract: Excitons in two-dimensional perovskites have been shown to exhibit diverse polaronic effects. This paper explores the consequences of these effects in many-body interactions involving excitons and phonon states. We interpret the observed weak interexciton and exciton-phonon dephasing rates as the consequence of polaronic protection effects.
15 citations
TL;DR: Preliminary transient absorption microscopy results for NPs internalized within the cells reveal the presence of long‐living species, further substantiating their relevance in biointerfaces.
Abstract: In this work the photophysics of poly(3-hexylthiophene) nanoparticles (NPs) is investigated in the context of their biological applications. The NPs, made as colloidal suspensions in aqueous buffers, present a distinct absorption band in the low-energy region. On the basis of systematic analysis of absorption and transient absorption (TA) spectra taken under different pH conditions, this band is associated with charge-transfer states generated by the polarization of loosely bound polymer chains and originating from complexes formed with electron-withdrawing species. Importantly, the ground-state depletion of these states upon photoexcitation is active even on microsecond timescales, thus suggesting that they act as precursor states for long-living polarons; this could be beneficial for cellular stimulation. Preliminary transient absorption microscopy results for NPs internalized within the cells reveal the presence of long-living species, further substantiating their relevance in biointerfaces.
11 citations
TL;DR: In this paper, the authors describe a theoretical description for entropy production in the scattering of an entangled biphoton Fock state within an optical cavity and show that in the limit of fast fluctuations, the entanglement entropy vanishes.
Abstract: Recent theories and experiments have explored the use of entangled photons as a spectroscopic probe of physical systems. We describe here a theoretical description for entropy production in the scattering of an entangled biphoton Fock state within an optical cavity. We develop this using perturbation theory by expanding the biphoton scattering matrix in terms of single-photon terms in which we introduce the photon-photon interaction via a complex coupling constant, ξ. We show that the von Neumann entropy provides a concise measure of this interaction. We then develop a microscopic model and show that in the limit of fast fluctuations, the entanglement entropy vanishes, whereas in the limit of slow fluctuations, the entanglement entropy depends on the magnitude of the fluctuations and reaches a maximum. Our result suggests that experiments measuring biphoton entanglement give microscopic information pertaining to exciton-exciton correlations.
11 citations
TL;DR: In this paper, the intrinsic and density-dependent exciton pure dephasing rates and their dependence on temperature were investigated in two-dimensional hybrid organic-inorganic metal-halide perovskites.
Abstract: In two-dimensional hybrid organic-inorganic metal-halide perovskites, the intrinsic optical lineshape reflects multiple excitons with distinct binding energies, each dressed differently by the hybrid lattice. Given this complexity, a fundamentally far-reaching issue is how Coulomb-mediated many-body interactions --- elastic scattering such as excitation-induced dephasing, inelastic exciton bimolecular scattering, and multi-exciton binding --- depend upon the specific exciton-lattice coupling. We report the intrinsic and density-dependent exciton pure dephasing rates and their dependence on temperature by means of a coherent nonlinear spectroscopy. We find exceptionally strong screening effects on multi-exciton scattering relative to other two-dimensional single-atomic-layer semiconductors. Importantly, the exciton-density dependence of the dephasing rates is markedly different for distinct excitons. These findings establish the consequences of particular lattice dressing on exciton many-body quantum dynamics, which critically define fundamental optical properties that underpin photonics and quantum optoelectronics in relevant exciton density regimes.
10 citations
TL;DR: In the version of this Article originally published, the units of the Fig. 3a x axis were incorrectly given as meV, which should have been eV.
Abstract: In the version of this Article originally published, the units of the Fig. 3a x axis were incorrectly given as meV. They should have been eV. This has now been corrected in all versions of the Article.
4 citations
TL;DR: In this article, a model for the scattering of an entangled pair of photons from a molecular dimer was developed and the von Neumann entropy of the outgoing bi-photon wave function was correlated to exciton exchange and repulsion interactions.
Abstract: Quantum entangled photons provide a sensitive probe of many-body interactions and offer an unique experimental portal for quantifying many-body correlations in a material system. In this paper, we present a theoretical demonstration of how photon-photon entanglement can be generated via interactions between coupled qubits. Here we develop a model for the scattering of an entangled pair of photons from a molecular dimer. We develop a diagrammatic theory for the scattering matrix and show that one can correlate the von Neumann entropy of the outgoing bi-photon wave function to exciton exchange and repulsion interactions. We conclude by discussing possible experimental scenarios for realizing these ideas.
4 citations
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TL;DR: In this paper, the authors 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.
Abstract: 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.