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Light-Matter Interactions at the Nanoscale and Quantum Electrodynamical Chemistry
Light-matter interaction is a fundamental issue in physics, chemistry, and engineering. The general research goal of my group is to understand the underlying principles of chemical systems coupled to the vacuum fluctuation of an electromagnetic field, and this emerging field is called “Polariton Chemistry” or “QED Chemistry”. When molecules strongly interact with a vacuum electromagnetic field, it is inadequate to describe their interactions simply using classical electrodynamics. In other words, traditional theories of spectroscopy, electronic structures, and chemical reactions are not valid in this condition. In order to incorporate the effect of the vacuum fluctuation into chemistry, a theoretical framework based on quantum electrodynamics is necessary. Currently, most research groups explore polariton chemistry based on cavity quantum electrodynamics or the Jaynes-Cummings model. However, existing theories can only be applied to an ideal cavity, and they cannot adequately describe molecules coupled to plasmon polaritons in a plasmonic cavity. In view of the limitations of the existing theories, I would like to develop new theories and computational methods in the framework of macroscopic quantum electrodynamics.
During the past few years, our group extended several traditional theories in chemical physics and generalized them in the version of macroscopic quantum electrodynamics.
Generalized fluorescence theory: This theory developed by our group can be regarded as a generalization of Chance-Prock-Silbey classical fluorescence theory, and it has been chosen as Editor’s Pick and Editors’ Choice in 2019 in The Journal of Chemical Physics [J. Chem. Phys. 2019, 151, 014105]. The follow-up studies include coherent-to-incoherent transition of molecular fluorescence [J. Phys. Chem. Lett. 2020, 11, 5948-5955], molecular emission power spectra based on macroscopic quantum electrodynamics [J. Chem. Phys. 2020, 153, 184102; J. Chem. Phys. 2021, 155, 074101], the mapping between macroscopic quantum electrodynamics and cavity quantum electrodynamics [J. Chem. Phys. 2021, 155, 134117; Front. Phys., 2022, 10:980167]. In addition, our group also collaborated with an experimental group and successfully elaborated the origin and the mechanism of molecular fluorescence enhancement from large-scale inhomogeneous plasmonic metal chips [Chem 2020, 6, 3396-3408].
Generalized energy transfer theory: The theory developed by Hsu can be viewed as a generalization of generalized Förster resonance energy transfer (FRET), and it has been chosen as Feature Article in Journal of Physical Chemistry Letters [J. Phys. Chem. Lett. 2017, 8, 2357-2367]. The theory can be applied to investigate the characteristic distance of energy transfer coupled to surface plasmon polaritons [J. Phys. Chem. Lett. 2018, 9, 7032-7039], localized surface plasmon polaritons [J. Phys. Chem. Lett. 2020, 11, 6796-6804], and cavity photons [J. Phys. Chem. C 2021, 125, 18119-18128]. The theory opens a promising direction for exploring exciton transport in plasmonic nanostructures, with possible applications in spectroscopy, photonics, biosensing, and energy devices [J. Chem, Phys. 2023, 159, 154701]. In addition, our group developed a transition-current-density approach to include non-point-dipole effect [Phys. Rev. A, 2023 107, 053709].
A unified theory of radiative and non-radiative electron transfer: Our group generalized the famous Marcus theory to include the radiative electron transfer process and developed a unified theory of electron transfer in the framework of quantum electrodynamics [J. Phys. Chem. Lett., 2022, 13, 9695-9702]. To incorporate macroscopic quantum electrodynamics into the electron transfer theory, our group developed a concept of "polaritonic Huang-Rhys factor" and quantify light–matter interactions in media [J. Phys. Chem. Lett. 2023, 14, 2395-2401].
Generalized internal conversion theory: Based on single-mode cavity quantum electrodynamics, our group generalized Lin's theory and Jortner's theory, and include quantum electrodynamic effects into the internal conversion processes [J. Phys. Chem. Lett. 2023, 14, 5924-5931].
QED multichromophoric Förster resonance energy transfer: In the framework of macroscopic quantum electrodynamics, our group generalized the theory of multichromophoric Förster resonance energy transfer to include polariton effects [J. Chem. Phys. 2022, 157, 184107; J. Chem. Phys. 2022, 157, 234109]. The thoery can be used to study the interplay between energy transfer and fluorescence in the presence of arbitrary inhomogeneous, dispersive, and absorbing media. However, the above theory lacks a correct quantitative description of intermolecular interactions. We improved the theory and cast it into a more rigorous version [Phys. Rev. A 2024, 109, 013717; J. Chem. Phys. 2024, 160, 114105]. The new theory is consistent with many famous results in quantum electrodynamics.
Nanoelectronics (Molecular Electronics and 2D Material Electronics)
In the next 5-20 years, 1-5 nm scale transistors (electronic devices) will emerge in the industry. At this scale, quantum, non-equilibrium, many-body, and interface effects become significantly important, and the electron transport properties of transistors cannot be simply described by the Boltzmann transport equation (diffusion or drift transport). Instead, full quantum mechanics simulations at the atomistic level are needed. However, most of the current quantum transport programs are based on a first-principle calculation, and in this framework it is challenging to simulate the full structure of a transistor (including source, drain, and gate) consisting of more than 10000 atoms. To solve this issue, our aim is to develop multiscale models combined with appropriate quantum transport techniques and apply them to investigate the next-generation electronics such as molecular electronics (e.g., molecular wires, carbon nanotubes), two dimensional electronics (e.g., graphene, molybdenum disulfide, black phosphorus), and spintronics. We have demonstrated several intriguing quantum transport phenomena in molecular electronics, including:
Franck-Condon blockade and charge stability diagram caused by vibronic couplings [1]
Light-driven electron transport: Photon-assisted tunneling, coherent destruction of tunneling, coherent revival of tunneling, quantum ratchet effects caused by AC driving fields [2][3][4][5]; Photo-induced anomalous Coulomb blockade [6][7]
Tunneling with destructive quantum interference caused by molecular electronic structure [8][9]
Conduction mechanism transition from tunneling to thermally activated hopping [10]
Geometry, temperature, and length dependence of conductance in oligomer systems [11][12][13]
The rule of molecular circuits in series and in parallel [14][15][16]
The effects of different types of metal strings on the conductance of the smallest electric wire [17][18][19]
Electric current fluctuations in a non-equilibrium open quantum system [20]
Many-body coherence [24]
Methodology of Quantum Transport Theory at the Nanoscale
Quantum transport is a subfield of condensed matter physics and nanotechnology, which focuses on the exchange of charges (e.g., electric current), energy (e.g., heat, exciton), and angular momentum (e.g., spin) between observed and studied systems at the nanoscale. The theory of quantum transport has been extensively applied to a variety of fields including mesoscopic physics, nanoelectronics, ultracold atoms, and DNA sequencing. Our group is interested in developing a new methodology to explore novel transport phenomena at the nanoscale. We have demonstrated several intriguing quantum transport phenomena based on the following methodologies:
Landauer approach [9][14][15]
Quantum scattering approach [2][3][4][5][8][11][12][13]
Non-equilibrium green’s function approach (Keldysh formalism) [17]
Rate equation approach [1][6][7][18]
Quantum master equation approach (Open quantum system techniques) [10][7][16][24]
Molecular Dynamics-Driven Liouville von Neumann Approach (Open quantum system techniques) [20]
Ultrafast Dynamics and Signal Processing
Electronic dynamics (attosecond science) in molecules and solid states is a fundamental topic in chemistry and physics. Traditionally, dynamics of a quantum system such as lifetime and energy difference can be revealed by spectral lines in the frequency domain by using the Fourier analysis, but the Fourier transform presents limited chronological information of a dynamical system. To explore chronological information in a quantum dynamical system, advanced signal processing techniques are needed. By using the new time-frequency methods developed by Prof. Hau-Tieng Wu and Dr. Yae-Lin Shue and the first-principle method (time-dependent generalized pseudospectral method) by Prof. Shih-I Chu, we can understand several fascinating phenomena in a hydrogen atom within a strong laser field [21] [22] [23]. In the future, our goal is to apply modern signal processing techniques to explore the electronic dynamics of molecules, monolayers, and 2d materials.
Reference (Further Information can be found in Publications)
[1] J. Chem. Phys., 2010, 133, 144705.
[2] Phys. Rev. Lett., 2012, 109, 186801.
[3] J. Chem. Phys., 2014, 141,124703.
[4] Phys. Rev. B, 2015, 92, 035410.
[5] Phys. Chem. Chem. Phys., 2015, 17, 20617-20629.
[6] Nano Lett., 2018, 18, 5015-5023.
[7] J. Chem. Phys., 2019, 151, 054704.
[8] Chem. Phys. Lett. 2008, 457, 279-283.
[9] Chem. Phys., 2009, 355, 177-182.
[10] J. Phys. Chem. Lett., 2014, 5, 1831-1836.
[11] Nano Lett., 2013, 13, 5020-5025.
[12] J. Phys. Chem. C, 2015, 119, 4753-4759.
[13] J. Chem. Phys., 2016, 145, 234702.
[14] J. Am. Chem. Soc., 2014, 136, 1832-1841.
[15] J. Am. Chem. Soc., 2015, 137, 5948-5954.
[16] Phys. Chem. Chem. Phys., 2016, 18, 32087-32095.
[17] J. Phys. Chem. C, 2008, 112, 10538-10541.
[18] Angew. Chem. Int. Ed., 2015, 54, 15734-15738. (Chosen as a very important article)
[19] Chem (Cell), 2017, 3, 373–379.
[20] J. Phys. Chem. C, 2019, 123, 10746-10755. (Invited Article, Special Issue -- Abraham Nitzan Festschrift)
[21] AIP Advances, 2014, 4, 117138.
[22] Opt. Express, 2015, 23, 30459-30482.
[23] Int. J. Data Sci. Anal. (JDSA), 2017, 3, 231-245.
[24] Phys. Rev. B, 2023, 108, 125422.
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