Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session B59: First-Principles Simulations of Excited-State Phenomena: Excitons and Bethe-Salpeter Equation IFocus
|
Hide Abstracts |
Sponsoring Units: DCOMP Chair: Talat Rahman, University of Central Florida Room: Room 301 |
Monday, March 6, 2023 11:30AM - 12:06PM |
B59.00001: Towards a unified ab initio description of excitations and their dynamics Invited Speaker: Claudia Draxl The interplay between electron-electron interaction, electron-vibrational coupling, electron-hole correlation, and (potentially) spin-orbit coupling (SOC) may give rise to exciting phenomena in the response of matter to light. Many-body perturbation theory (MBPT), in particular the Bethe-Salpeter equation, is the method of choice for tackling such problems to describe what is happening in experimental probes like photoemission, optical and x-ray absorption, electron-loss spectroscopy, etc. In this talk, I will provide examples along these lines, providing in-depth analysis of the underlying processes. These examples include exciton-exciton coupling in resonant inelastic x-ray scattering (RIXS) in oxides, the structural relaxation in optically excited molecules, or the impact of vibrations and/or SOC in the optical absorption spectra of different materials. Furthermore, I will discuss first steps towards the description of time-resolved processes. All methods are implemented in the full-potential code exciting whose all-electron nature allows for treating valence and core excitations on the same footing, also fully accounting for SOC. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B59.00002: First-principles calculations of excitons including radiative recombination and polaritonic effects: the retarded Bethe-Salpeter equation Zachary N Mauri, Christopher J Ciccarino, Felipe H da Jornada Recent research in 2D materials has revealed a host of phenomena only present in low-dimensional systems, such as the presence of strongly bound excitons due to the electronic confinement and weak dielectric screening in such systems. The electronic and optical properties in such systems have been largely captured with success through first-principles techniques based on interacting Green's function formalisms, such as the ab initio GW and Bethe-Salpeter equation approaches, respectively. However, these methods are typically derived assuming instantaneous many-electron interactions. Here, we describe a formalism to include retardation effects into the Bethe-Salpeter equation that is computationally efficient and gauge invariant. While previous efforts have focused on the effect of retardation effects in the direct (screened) electron-hole interactions, we find here that retardation effects in the (bare) exchange interactions dominate in low dimensions. Our work predicts a renormalization of the exciton dispersion and a broadening of the exciton dispersion when retardation effects are included. More broadly, our approach can be applied to the study of polaritonic effects directly from standard interacting Green's-function formalisms. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B59.00003: Phonon-assisted Photoluminescence and Exciton Lifetime in Solids from First Principles Chunhao Guo, Junqing Xu, Yuan Ping Time-resolved photoluminescence spectroscopy (TRPL) reveals many important dynamical many-body phenomena including phonon-assisted recombination of indirect excitons. However, such signatures in the PL spectrum and their dynamical processes are not yet been fully understood at an atomistic level. We present a universal first-principles methodology based on Heisenberg equation of motion to calculate the phonon-assisted photoluminescence spectrum and exciton lifetime at finite temperature. In particular, this approach can describe the exciton lifetime including both radiative recombination and exciton-phonon scattering simultaneously from first-principles. We further analyze the phonon mode contribution and emphasize the relaxation pathway and dephasing lifetime through each scattering channel to explain the experimental measurements in vdW layered materials. We emphasize that first-principles phonon-assisted transitions are crucial for an in-depth understanding of exciton dynamics in solids. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B59.00004: Excited-state force calculations from GW/BSE and DFPT: development and application to organic metal halide perovskites Rafael R Del Grande, David A Strubbe While absorption of light has been long studied in electronic structure, the interactions of the resulting excited states with the lattice that cause light-induced structural changes remain hard to handle. This is an underlying phenomenon for photodegradation, Stokes shifts, exciton transport, and other photophysics, which can be studied via excited-state forces. Ismail-Beigi and Louie [Phys. Rev. Lett. 90, 076401 (2003)] developed an approximate theory combining quasiparticle and excitonic effects from GW and Bethe-Salpeter Equation (BSE) with electron-phonon interactions from Density Functional Perturbation Theory, but this approach has been little used. We revisit this theory, with improvements to the underlying approximations, and implement it in a practical workflow for BerkeleyGW. We make detailed tests of the validity of these approximations and demonstrate favorable convergence properties that make the forces less time-consuming than ordinary GW/BSE. Then we explore some applications to methylammonium lead iodide perovskites, whose use in solar cells is limited by photodegradation. We study the equilibrium structures of the excited states, and coupling between different excitons due to the phonons, to give insight into the photophysics of perovskites. |
Monday, March 6, 2023 12:42PM - 12:54PM |
B59.00005: Excitonic effects on nonlinear optical responses from first principles Yang-hao Chan, Steven G Louie, Jiawei Ruan
|
Monday, March 6, 2023 12:54PM - 1:06PM |
B59.00006: Vertical excitation energies of the SiV(0) defect in diamond computed by the Spin-Flip Bethe-Salpeter Equation approach Bradford A Barker, David A Strubbe The neutral silicon-vacancy defect in diamond (“SiV(0)”) is a promising candidate for qubit and nanosensing applications, and unlike the well-studied NV- center, possesses inversion symmetry. As a potential qubit, optical transition energies from the defect’s triplet ground state to its triplet excited states are important quantities to calculate. Compared to the NV- center, however, there are fewer calculations of these transition energies. As the defect has an open-shell electronic structure, computational methods must capture the multiconfigurational nature of its ground and excited states. We present calculations of singlet and triplet vertical excitation energies (that is, relative to the ground state energy at the ground state atomic coordinates) computed via the Spin-Flip Bethe-Salpeter Equation approach (“SF-BSE,” arXiv:2207.04549). SF-BSE is a method based on many-body perturbation theory that allows for the simultaneous computation of ground and excited state energies, from a basis of “target” states constructed from exciting an occupied up-spin electron to an unoccupied down-spin empty orbital. While some excited states for the NV- defect have contributions from double-excitations that are inaccessible via single-reference spin-flip methods, the excited states of interest for SiV(0) do not, allowing for improved quantitative agreement for vertical excitation energies. Results from this approach are compared to other multireference methods in the literature. |
Monday, March 6, 2023 1:06PM - 1:18PM |
B59.00007: Engineering intermediate band states in Cu-intercalated 2D transition metal chalcogenides Srihari M Kastuar, Chinedu E Ekuma Intercalated layered transition metal chalcogenides and metal atom hybrids have been shown to have remarkable properties with a high degree of tunability. Herein, we have studied the optoelectric properties of hybrid structures derived from Cu-intercalated atomically thin GeSe/SnS heterostructures. Using the Green's function and Coulomb interaction and Bethe-Salpeter equation approaches, we determined the single-particle electronic and two-particle absorption properties. In the hybrid materials, we find intermediate band (IB) states with subband gap values of 0.78 and 1.26 eV, which are remarkably close to the subband gaps (~0.71 and 1.24 eV) for IB solar cell materials predicted by the Luque-Marti model. |
Monday, March 6, 2023 1:18PM - 1:30PM |
B59.00008: A theoretical design of two-dimensional thermally activated delayed fluorescence material Siyu Gao Organic light-emitting diodes (OLEDs) have attracted great interest for display and lighting applications. Now, Thermally Activated Delayed Fluorescence (TADF) based OLEDs may possess a nearly 100% internal quantum efficiency. In this work, a two-dimentional TADF material is designed based on multiple resonance (MR) effect and density functional theory (DFT) grid search of the potential energy surface (PES) at an optimum interlayer distance. An energy barrier of 0.2 eV is observed between singlet and triplet state. The projected band structure by DFT shows the distribution of donor and acceptor. The quasipartical band structure and exciton wavefunctions simulated by GW approximation and the Bethe-Salpeter equation is reported. |
Monday, March 6, 2023 1:30PM - 1:42PM |
B59.00009: Exchange-Driven Intermixing of Bulk and Topological Surface State by Chiral Excitons in Bi2Se3 Bowen Hou, Dan Wang, Bradford A Barker, Diana Y Qiu Topological surface states (TSS) in the topological insulator Bi2Se3 are often characterized using light-based probes, such as the circular photoelectric effect. However, microscopic theory considering electron-hole interactions and their effect on the optical response of TSS and surface localization has not yet been explored. Here, we study excitonic effects in the bulk and surface of Bi2Se3 using the ab initio GW and Bethe-Salpeter equation (GW-BSE) approach with a fully-relativistic spinor formalism. We identify bright excitons with p-like symmetry, as well as multiple series of excitons with chiral optical dipole selection rules spread over a wide energy range of 0-2.82 eV. The electron-hole pair forming the chiral excitons exhibit the characters of both bulk states and topologically protected surface states, which are intermixed by the Coulomb exchange interaction. Our results address fundamental questions about the degree to which electron-hole interactions can relax the topological protection of surface states in topological insulators by elucidating the complex intermixture of bulk and surface states excited in optical measurements and their coupling to light. |
Monday, March 6, 2023 1:42PM - 1:54PM |
B59.00010: Flat-band induced excitonic insulator in a carbon-based, triangulene Kagome lattice Jingwei Jiang, Aidan Delgado, Carolin Dusold, Adam Cronin, Felix R Fischer, Steven G Louie Excitonic insulator (EI) is a novel cooperative phase of matter formed by coherent excitons. This phase occurs when the bound electron-hole excitations of the system have a lower energy than the normal band insulating ground state. Namely, when an electron from the valence band is put in the conduction band, the binding energy between the excited electrons and holes is larger than the bandgap of the normal state, leading to simultaneous formation and subsequent condensation of excitons. A previous work shows that a specific 2-dimensional crystal of finite-size graphene triangles, a [4]triangulene Kagome lattice, possesses negative excitation energies of triplet excitons via a GW-BSE on top of DFT-LDA calculation[1], and thus could be a candidate for EI. Here we study the coherent ground state formed by excitons using a BCS-like theory, and explore the experimental signatures of such EI state (such as the local density of state (LDOS) and other electronic properties) from first-principles calculations. Our results agree well with STM measurements performed by our experimental collaborators. We also discuss the interplay between possible magnetic state, exciton condensation state, and normal state, as well as considering substrate effects. |
Monday, March 6, 2023 1:54PM - 2:06PM |
B59.00011: Excitonic near resonance-enhancement of shift currents in monolayer NbOCl2 MingRui Lai The shift current is a static nonlinear photocurrent exhibited by crystals lacking center-of-inversion symmetry. Such photocurrents have been widely studied for their potential photovoltaic applications and have potential to go beyond the Shockley-Queisser limit. As such, an accurate theoretical description of the phenomenon is essential for material design. Density functional theory is often utilized in first principles calculations of the shift current, treating the electrons independently. In 2D materials however, the reduced screening results in signficant many-body interactions and photo-excitations are more accurately described with excitons. We have developed a theoretical framework which captures these excitonic effects using many-body perturbation theory within the framework of nonlinear optical response. We derive an expression for the exciton shift current from the static nonlinear response. The many-body excited states are obtained using the GW-BSE formalism by solving the Bethe-Salpeter Equation with quasi-particle energies. Using the many-body excited states, we then compute the excitonic shift current. We show that there is a large enhancement in the shift current when considering many-body interactions, mainly due to the near-resonance condition between two near-degenerate excited states. |
Monday, March 6, 2023 2:06PM - 2:18PM |
B59.00012: Excitonic properties of monolayer and bulk hexagonal boron nitride Woncheol Lee, Ping Wang, Qiannan Wen, Zetian Mi, Mackillo Kira, Emmanouil Kioupakis In this work, we investigate the excitonic properties of monolayer and bulk hexagonal boron nitride (h-BN) based on density functional theory and many-body perturbation theory. Our simulation results indicate that monolayer h-BN on Highly Ordered Pyrolytic Graphite (HOPG) exhibit a giant renormalization of the electronic band gap and the exciton binding energy due to the strong screening induced by the HOPG substrate. Our photoluminescence measurements and reflectance measurements confirm our theoretical prediction on the electronic and optical gap. In addition, we perform first-principles calculations on the exciton-phonon coupling matrix elements and reveal that the strong exciton-phonon interaction contributes to the effective indirect optical transitions and the bright luminescence in h-BN. As a result, we propose that both the strong screening from the substrate and the strong exciton-phonon interaction within h-BN should be considered as an important factor for exciton engineering in h-BN. The work is supported by the University of Michigan College of Engineering Blue Sky Research Program. W.L. was partially supported by the Kwanjeong Educational Foundation Scholarship. Computational resources were provided by the DOE NERSC facility. |
Monday, March 6, 2023 2:18PM - 2:30PM |
B59.00013: First-Principles Study of the Doping-dependent Exciton and Trion Linewidth in Monolayer MoTe2 Supavit Pokawanvit, Aurelie Champagne, Jonah B Haber, Diana Y Qiu, Jeffrey B Neaton, Felipe H Jornada The linewidth of excitonic complexes provides direct insights into the nature of optical excitations in materials and their decay pathways. In doped semiconducting monolayers of transition metal dichalcogenides (TMDs), the linewidth associated with an exciton resonance is sensitive to extra charge carriers due to the nontrivial dielectric screening from the Fermi sea and the variety of states an exciton can scatter to, even in the weak-doping limit. Therefore, computational approaches and first-principles calculations can provide unique insights into the microscopic origin of such interactions and the nature of the associated scattering events. In this talk, we present results from first-principles calculations of Dyson-like equations associated with 3- and 4-body interacting particle problems (involving electrons and holes) to address this problem. We compare our results with perturbative calculations based on the scattering of excitons to Fermi-sea electron-hole pairs and assess the importance of many-body screening, band-filling effects, and the ab initio description of electron-hole coupling terms. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700