Periodic Reporting for period 1 - CompExDyn (Complex Exciton Dynamics in Materials: a First-Principles Computational Approach)
Período documentado: 2022-02-01 hasta 2024-07-31
Light-matter interactions determine materials’ functionality in emerging applications, such as energy conversion and storage and quantum information processing. Excitons, correlated electron-hole pairs bound together by a Coulomb interaction, often serve as the main energy carriers, with their lifetime and decay dynamics dominating the energy-transfer efficiency. Low-dimensional excitonic semiconductor systems, such as organic molecular crystals, transition metal dichalcogenides (TMDs), and layered hybrid perovskites, hold strongly-bound, long-lived excitons- a typical feature due the reduced dimensionality. In these materials, structural tunability offers the controllable excited-state setting needed to optimize device functionality. Direct imaging of exciton propagation is possible via advanced ultrafast microscopy, allowing the observation and examination of exciton relaxation and processes through a propagating wavepacket picture, and revealing a wealth of exciton scattering mechanisms and decay pathways.
A key factor that impacts exciton dynamics is structural modifications in the interacting material. Local structural effects, such as atomic defects, heterostructure compositions, and crystal fluctuations, can vastly increase carrier mobility, allowing enhanced catalytic and transport activity. A theoretical understanding of such a complex excitonic picture must assess a variety of electron-hole transitions with modified quantum selection rules associated with the structural modifications. Yet, a theory that accounts for the interplay between local modifications of the crystal environment and their effect on exciton relaxation processes is lacking, highlighting the need for a predictive, structure-sensitive theory of the underlying structure-dynamics relations.
This project involves the derivation, implementation, and application of predictive computational and theoretical methods to understand the fundamental dynamics that govern light-matter interactions in materials. We explore emerging low-dimensional semiconducting materials of interest for renewable energy and quantum information science. For these materials, vast experimental data enables careful validation and ultimately the development of a reliable theory, aiming at reaching comprehensive understanding of the relation between the atomistic material structure and the light harvesting efficiency. Specifically, we are deriving and using many-body first-principles approaches to numerically evaluate complex interactions dominating the excited-state dynamical mechanisms involved in the light energy transfer in the material.
Our research is divided to three main parts: derivation of first-principles approaches to excited-state dynamics in materials; application to low-dimensional semiconducting materials of complex structures; and derivation of theoretical extensions beyond common approximations on the interaction strengths. This is achieved within the three objectives discussed below.
A key factor that impacts exciton dynamics is structural modifications in the interacting material. Local structural effects, such as atomic defects, heterostructure compositions, and crystal fluctuations, can vastly increase carrier mobility, allowing enhanced catalytic and transport activity. A theoretical understanding of such a complex excitonic picture must assess a variety of electron-hole transitions with modified quantum selection rules associated with the structural modifications. Yet, a theory that accounts for the interplay between local modifications of the crystal environment and their effect on exciton relaxation processes is lacking, highlighting the need for a predictive, structure-sensitive theory of the underlying structure-dynamics relations.
This project involves the derivation, implementation, and application of predictive computational and theoretical methods to understand the fundamental dynamics that govern light-matter interactions in materials. We explore emerging low-dimensional semiconducting materials of interest for renewable energy and quantum information science. For these materials, vast experimental data enables careful validation and ultimately the development of a reliable theory, aiming at reaching comprehensive understanding of the relation between the atomistic material structure and the light harvesting efficiency. Specifically, we are deriving and using many-body first-principles approaches to numerically evaluate complex interactions dominating the excited-state dynamical mechanisms involved in the light energy transfer in the material.
Our research is divided to three main parts: derivation of first-principles approaches to excited-state dynamics in materials; application to low-dimensional semiconducting materials of complex structures; and derivation of theoretical extensions beyond common approximations on the interaction strengths. This is achieved within the three objectives discussed below.
Objective I: Method derivation.
Over the past few years, our group has pioneered a novel approach for calculating exciton propagation resulting from ultrafast processes following a photoexcitation in low-dimensional crystals. As a first step, and in collaboration with the Qiu group at Yale University, we derived a first-principles computational approach to wavepacket propagation that includes ab initio information of the exciton band structure. We showed that long-range exchange interactions can give rise to exciton dispersion with nonanalytic discontinuities in the momentum coordinate, a direct result of the system symmetry and dimensionality (Qiu et al., Nano Lett. 2021).
We followed with the derivation of a first-principles approach to compute exciton propagation and relaxation while including exciton-phonon scattering in crystals (Cohen et al., Phys. Rev. Lett. 2024).
We further introduced an approach connecting our studies with algorithms within artificial intelligence. We developed a method of resolving the correlation-induced spatial-temporal dynamics via singular value decomposition (Baratz et al., Under Review 2024).
In addition, we have derived a Lindblad formalism within a density-matrix framework, where we explicitly determine the time-resolved, phonon-induced relaxation of excitons within the femtosecond (fs) regime and while keeping the structural information encoded within the band-structure approaches building the exciton and phonon states participating in the interaction (Amit et al., Phys. Rev. B 2023).
Objective II: Method application.
Our group has been extensively exploring quasiparticle and excitonic properties upon the presence of atomic defects in 2D transition metal dichalcogenides (TMDs), semiconductors with strongly bound excitons. Our initial studies demonstrated that point chalcogen vacancies in TMD layered materials introduce mixed electron-hole transitions, resulting in a low-energy optical signature (Amit et al., Phys. Rev. B 2022), further confirmed in experiment (Hötger et al., npj 2D Mater. Appl. 2023; Hötger et al., Nano Lett. 2023).
To study the effect of twist angle between the layers, we developed a scheme for unfolding the electronic bandstructure and exciton components onto the Brillouin Zone of the constituent layers. Our analysis reveals a unique momentum-mixed excitonic nature, with states that are comprised of both inter- and intra-layer electron-hole excitations (Kundu et al., npj Comp. Mater. 2023).
We further computed the electronic transport through defect states across TMD monolayers adsorbed on graphene (Hernangómez-Pérez et al., Nano Lett. 2023) and explored the effect of interlayer twist angle on the excitonic states in heterostructures of layered TMDs and graphene (Kleiner et al., npj 2D mater. 2024).
Objective III: Method extension.
This part of the project is still ongoing. We develop an extension of density functional theory to mutually compute both electronic and nuclei wavefunctions in a self-consistent cycle, based on the exact factorization method and extended to periodic materials, in collaboration with the Gross group at the Hebrew University. We are currently writing a manuscript describing our results.
Over the past few years, our group has pioneered a novel approach for calculating exciton propagation resulting from ultrafast processes following a photoexcitation in low-dimensional crystals. As a first step, and in collaboration with the Qiu group at Yale University, we derived a first-principles computational approach to wavepacket propagation that includes ab initio information of the exciton band structure. We showed that long-range exchange interactions can give rise to exciton dispersion with nonanalytic discontinuities in the momentum coordinate, a direct result of the system symmetry and dimensionality (Qiu et al., Nano Lett. 2021).
We followed with the derivation of a first-principles approach to compute exciton propagation and relaxation while including exciton-phonon scattering in crystals (Cohen et al., Phys. Rev. Lett. 2024).
We further introduced an approach connecting our studies with algorithms within artificial intelligence. We developed a method of resolving the correlation-induced spatial-temporal dynamics via singular value decomposition (Baratz et al., Under Review 2024).
In addition, we have derived a Lindblad formalism within a density-matrix framework, where we explicitly determine the time-resolved, phonon-induced relaxation of excitons within the femtosecond (fs) regime and while keeping the structural information encoded within the band-structure approaches building the exciton and phonon states participating in the interaction (Amit et al., Phys. Rev. B 2023).
Objective II: Method application.
Our group has been extensively exploring quasiparticle and excitonic properties upon the presence of atomic defects in 2D transition metal dichalcogenides (TMDs), semiconductors with strongly bound excitons. Our initial studies demonstrated that point chalcogen vacancies in TMD layered materials introduce mixed electron-hole transitions, resulting in a low-energy optical signature (Amit et al., Phys. Rev. B 2022), further confirmed in experiment (Hötger et al., npj 2D Mater. Appl. 2023; Hötger et al., Nano Lett. 2023).
To study the effect of twist angle between the layers, we developed a scheme for unfolding the electronic bandstructure and exciton components onto the Brillouin Zone of the constituent layers. Our analysis reveals a unique momentum-mixed excitonic nature, with states that are comprised of both inter- and intra-layer electron-hole excitations (Kundu et al., npj Comp. Mater. 2023).
We further computed the electronic transport through defect states across TMD monolayers adsorbed on graphene (Hernangómez-Pérez et al., Nano Lett. 2023) and explored the effect of interlayer twist angle on the excitonic states in heterostructures of layered TMDs and graphene (Kleiner et al., npj 2D mater. 2024).
Objective III: Method extension.
This part of the project is still ongoing. We develop an extension of density functional theory to mutually compute both electronic and nuclei wavefunctions in a self-consistent cycle, based on the exact factorization method and extended to periodic materials, in collaboration with the Gross group at the Hebrew University. We are currently writing a manuscript describing our results.
The theory derivations we already achieved are new and beyond the state of the art. Our results are publicly available and we occasionally present them at meetings and conferences. We have established several collaborations with experimental groups to work together on understanding their related observations.
Our theory development involves numerical theories of complex dynamics. These methods, derived in our case for quantum systems, are directly applicable in materials science, condensed matter physics, and quantum chemistry. In more general terms, treating complex dynamics numerically exact is a challenge relevant across many fields, from engineering to medicine to social sciences. The method we started establishing using AI-based approaches is a showcase for this applicability.
Key needs to ensure further success involve:
(i) Application of ab initio approaches to dynamics in structurally complex structures, for further merging of objectives I and II. We are in the early stages of this part of the research.
(ii) Finalization and demonstration of the theory derived in Objective III. This part mainly demands further research and is expected to last for the remaining of the ERC grant period.
Our theory development involves numerical theories of complex dynamics. These methods, derived in our case for quantum systems, are directly applicable in materials science, condensed matter physics, and quantum chemistry. In more general terms, treating complex dynamics numerically exact is a challenge relevant across many fields, from engineering to medicine to social sciences. The method we started establishing using AI-based approaches is a showcase for this applicability.
Key needs to ensure further success involve:
(i) Application of ab initio approaches to dynamics in structurally complex structures, for further merging of objectives I and II. We are in the early stages of this part of the research.
(ii) Finalization and demonstration of the theory derived in Objective III. This part mainly demands further research and is expected to last for the remaining of the ERC grant period.