Felipe Jornada's research aims at predicting and understanding excited-state phenomena in quantum and energy materials. In order to make reliable predictions on novel materials, he relies on high-performance computer calculations based on parameter-free, quantum-mechanical theories that are developed in his group. He is interested in studying fundamental aspects of these excitations – their lifetimes, dynamics, and stability/binding energies – and how they can be engineered in novel materials, such as nanostructured and low-dimensional systems. His ultimate goal is to use insights from atomistic calculations to rationally design new materials with applications in energy research, electronics, optoelectronics, and quantum technologies.

Felipe received his Ph.D. degree in physics from UC Berkeley in 2017 under the advice of Prof. Steven G. Louie. His Ph.D. research focused on the prediction of the electronic and optical properties of new quasi-two-dimensional materials, such as graphene and monolayer transition metal dichalcogenides. In his postdoc, he studied a number of problems related to multiparticle excitations in low-dimensional materials, including biexcitons and plasmons. Felipe joined the Stanford faculty in January 2020 and an assistant professor in the Department of Materials Science and Engineering.

Academic Appointments

Honors & Awards

  • CAREER Award, National Science Foundation (2023)
  • Jagdeep & Roshni Singh Faculty Fellow, Stanford University (2020 – 2022)
  • Best Thesis Prize, Kavli Energy NanoScience Institute, UC Berkeley (2017)

Professional Education

  • Ph.D., UC Berkeley, Physics (2017)
  • M.S., Federal University of Rio Grande do Sul, Brazil, Physics (2010)
  • B.A., Federal University of Rio Grande do Sul, Brazil, Physics (2007)

2023-24 Courses

Stanford Advisees

All Publications

  • Mixed Stochastic-Deterministic Approach for Many-Body Perturbation Theory Calculations. Physical review letters Altman, A. R., Kundu, S., da Jornada, F. H. 2024; 132 (8): 086401


    We present an approach for GW calculations of quasiparticle energies with quasiquadratic scaling by approximating high-energy contributions to the Green's function in its Lehmann representation with effective stochastic vectors. The method is easy to implement without altering the GW code, converges rapidly with stochastic parameters, and treats systems of various dimensionality and screening response. Our calculations on a 5.75° twisted MoS_{2} bilayer show how large-scale GW methods include geometry relaxations and electronic correlations on an equal basis in structurally nontrivial materials.

    View details for DOI 10.1103/PhysRevLett.132.086401

    View details for PubMedID 38457735

  • Hidden phonon highways promote photoinduced interlayer energy transfer in twisted transition metal dichalcogenide heterostructures. Science advances Johnson, A. C., Georgaras, J. D., Shen, X., Yao, H., Saunders, A. P., Zeng, H. J., Kim, H., Sood, A., Heinz, T. F., Lindenberg, A. M., Luo, D., da Jornada, F. H., Liu, F. 2024; 10 (4): eadj8819


    Vertically stacked van der Waals (vdW) heterostructures exhibit unique electronic, optical, and thermal properties that can be manipulated by twist-angle engineering. However, the weak phononic coupling at a bilayer interface imposes a fundamental thermal bottleneck for future two-dimensional devices. Using ultrafast electron diffraction, we directly investigated photoinduced nonequilibrium phonon dynamics in MoS2/WS2 at 4° twist angle and WSe2/MoSe2 heterobilayers with twist angles of 7°, 16°, and 25°. We identified an interlayer heat transfer channel with a characteristic timescale of ~20 picoseconds, about one order of magnitude faster than molecular dynamics simulations assuming initial intralayer thermalization. Atomistic calculations involving phonon-phonon scattering suggest that this process originates from the nonthermal phonon population following the initial interlayer charge transfer and scattering. Our findings present an avenue for thermal management in vdW heterostructures by tailoring nonequilibrium phonon populations.

    View details for DOI 10.1126/sciadv.adj8819

    View details for PubMedID 38266081

  • Bidirectional phonon emission in two-dimensional heterostructures triggered by ultrafast charge transfer. Nature nanotechnology Sood, A., Haber, J. B., Carlström, J., Peterson, E. A., Barre, E., Georgaras, J. D., Reid, A. H., Shen, X., Zajac, M. E., Regan, E. C., Yang, J., Taniguchi, T., Watanabe, K., Wang, F., Wang, X., Neaton, J. B., Heinz, T. F., Lindenberg, A. M., da Jornada, F. H., Raja, A. 2022


    Photoinduced charge transfer in van der Waals heterostructures occurs on the 100 fs timescale despite weak interlayer coupling and momentum mismatch. However, little is understood about the microscopic mechanism behind this ultrafast process and the role of the lattice in mediating it. Here, using femtosecond electron diffraction, we directly visualize lattice dynamics in photoexcited heterostructures of WSe2/WS2 monolayers. Following the selective excitation of WSe2, we measure the concurrent heating of both WSe2 and WS2 on a picosecond timescale-an observation that is not explained by phonon transport across the interface. Using first-principles calculations, we identify a fast channel involving an electronic state hybridized across the heterostructure, enabling phonon-assisted interlayer transfer of photoexcited electrons. Phonons are emitted in both layers on the femtosecond timescale via this channel, consistent with the simultaneous lattice heating observed experimentally. Taken together, our work indicates strong electron-phonon coupling via layer-hybridized electronic states-a novel route to control energy transport across atomic junctions.

    View details for DOI 10.1038/s41565-022-01253-7

    View details for PubMedID 36543882

  • Optical absorption of interlayer excitons in transition-metal dichalcogenide heterostructures. Science (New York, N.Y.) Barre, E., Karni, O., Liu, E., O'Beirne, A. L., Chen, X., Ribeiro, H. B., Yu, L., Kim, B., Watanabe, K., Taniguchi, T., Barmak, K., Lui, C. H., Refaely-Abramson, S., da Jornada, F. H., Heinz, T. F. 2022; 376 (6591): 406-410


    Interlayer excitons, electron-hole pairs bound across two monolayer van der Waals semiconductors, offer promising electrical tunability and localizability. Because such excitons display weak electron-hole overlap, most studies have examined only the lowest-energy excitons through photoluminescence. We directly measured the dielectric response of interlayer excitons, which we accessed using their static electric dipole moment. We thereby determined an intrinsic radiative lifetime of 0.40 nanoseconds for the lowest direct-gap interlayer exciton in a tungsten diselenide/molybdenum diselenide heterostructure. We found that differences in electric field and twist angle induced trends in exciton transition strengths and energies, which could be related to wave function overlap, moire confinement, and atomic reconstruction. Through comparison with photoluminescence spectra, this study identifies a momentum-indirect emission mechanism. Characterization of the absorption is key for applications relying on light-matter interactions.

    View details for DOI 10.1126/science.abm8511

    View details for PubMedID 35446643

  • Structure of the moire exciton captured by imaging its electron and hole. Nature Karni, O., Barre, E., Pareek, V., Georgaras, J. D., Man, M. K., Sahoo, C., Bacon, D. R., Zhu, X., Ribeiro, H. B., O'Beirne, A. L., Hu, J., Al-Mahboob, A., Abdelrasoul, M. M., Chan, N. S., Karmakar, A., Winchester, A. J., Kim, B., Watanabe, K., Taniguchi, T., Barmak, K., Madeo, J., da Jornada, F. H., Heinz, T. F., Dani, K. M. 2022; 603 (7900): 247-252


    Interlayer excitons (ILXs) - electron-hole pairs bound across two atomically thin layered semiconductors - have emerged as attractive platforms to study exciton condensation1-4, single-photon emission and other quantum information applications5-7. Yet, despite extensive optical spectroscopic investigations8-12, critical information about their size, valley configuration and the influence of the moire potential remains unknown. Here, in a WSe2/MoS2 heterostructure, we captured images of the time-resolved and momentum-resolved distribution of both of the particles that bind to form the ILX: the electron and the hole. We thereby obtain a direct measurement of both the ILX diameter of around 5.2nm, comparable with the moire-unit-cell length of 6.1nm, and the localization of its centre of mass. Surprisingly, this large ILX is found pinned to a region of only 1.8nm diameter within the moire cell, smaller than the size of the exciton itself. This high degree of localization of the ILX is backed by Bethe-Salpeter equation calculations and demonstrates that the ILX can be localized within small moire unit cells. Unlike large moire cells, these are uniform over large regions, allowing the formation of extended arrays of localized excitations for quantum technology.

    View details for DOI 10.1038/s41586-021-04360-y

    View details for PubMedID 35264760

  • Giant exciton-enhanced shift currents and direct current conduction with subbandgap photo excitations produced by many-electron interactions PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Chan, Y., Qiu, D. Y., da Jornada, F. H., Louie, S. G. 2021; 118 (25)


    Shift current is a direct current generated from nonlinear light-matter interaction in a noncentrosymmetric crystal and is considered a promising candidate for next-generation photovoltaic devices. The mechanism for shift currents in real materials is, however, still not well understood, especially if electron-hole interactions are included. Here, we employ a first-principles interacting Green's-function approach on the Keldysh contour with real-time propagation to study photocurrents generated by nonlinear optical processes under continuous wave illumination in real materials. We demonstrate a strong direct current shift current at subbandgap excitation frequencies in monolayer GeS due to strongly bound excitons, as well as a giant excitonic enhancement in the shift current coefficients at above bandgap photon frequencies. Our results suggest that atomically thin two-dimensional materials may be promising building blocks for next-generation shift current devices.

    View details for DOI 10.1073/pnas.1906938118

    View details for Web of Science ID 000671755600007

    View details for PubMedID 34155136

    View details for PubMedCentralID PMC8237677

  • Experimental measurement of the intrinsic excitonic wave function. Science advances Man, M. K., Madeo, J., Sahoo, C., Xie, K., Campbell, M., Pareek, V., Karmakar, A., Wong, E. L., Al-Mahboob, A., Chan, N. S., Bacon, D. R., Zhu, X., Abdelrasoul, M. M., Li, X., Heinz, T. F., da Jornada, F. H., Cao, T., Dani, K. M. 2021; 7 (17)


    An exciton, a two-body composite quasiparticle formed of an electron and hole, is a fundamental optical excitation in condensed matter systems. Since its discovery nearly a century ago, a measurement of the excitonic wave function has remained beyond experimental reach. Here, we directly image the excitonic wave function in reciprocal space by measuring the momentum distribution of electrons photoemitted from excitons in monolayer tungsten diselenide. By transforming to real space, we obtain a visual of the distribution of the electron around the hole in an exciton. Further, by also resolving the energy coordinate, we confirm the elusive theoretical prediction that the photoemitted electron exhibits an inverted energy-momentum dispersion relationship reflecting the valence band where the partner hole remains, rather than that of conduction band states of the electron.

    View details for DOI 10.1126/sciadv.abg0192

    View details for PubMedID 33883143

  • Universal slow plasmons and giant field enhancement in atomically thin quasi-two-dimensional metals. Nature communications da Jornada, F. H., Xian, L., Rubio, A., Louie, S. G. 2020; 11 (1): 1013


    Plasmons depend strongly on dimensionality: while plasmons in three-dimensional systems start with finite energy at wavevector q=0, plasmons in traditional two-dimensional (2D) electron gas disperse as [Formula: see text]. However, besides graphene, plasmons in real, atomically thin quasi-2D materials were heretofore not well understood. Here we show that the plasmons in real quasi-2D metals are qualitatively different, being virtually dispersionless for wavevectors of typical experimental interest. This stems from a broken continuous translational symmetry which leads to interband screening; so, dispersionless plasmons are a universal intrinsic phenomenon in quasi-2D metals. Moreover, our ab initio calculations reveal that plasmons of monolayer metallic transition metal dichalcogenides are tunable, long lived, able to sustain field intensity enhancement exceeding 107, and localizable in real space (within ~20nm) with little spreading over practical measurement time. This opens the possibility of tracking plasmon wave packets in real time for novel imaging techniques in atomically thin materials.

    View details for DOI 10.1038/s41467-020-14826-8

    View details for PubMedID 32081895

  • Origins of Singlet Fission in Solid Pentacene from an ab initio Green's Function Approach PHYSICAL REVIEW LETTERS Refaely-Abramson, S., da Jornada, F. H., Louie, S. G., Neaton, J. B. 2017; 119 (26): 267401


    We develop a new first-principles approach to predict and understand rates of singlet fission with an ab initio Green's-function formalism based on many-body perturbation theory. Starting with singlet and triplet excitons computed from a GW plus Bethe-Salpeter equation approach, we calculate the exciton-biexciton coupling to lowest order in the Coulomb interaction, assuming a final state consisting of two noninteracting spin-correlated triplets with finite center-of-mass momentum. For crystalline pentacene, symmetries dictate that the only purely Coulombic fission decay process from a bright singlet state requires a final state consisting of two inequivalent nearly degenerate triplets of nonzero, equal and opposite, center-of-mass momenta. For such a process, we predict a singlet lifetime of 30-70 fs, in very good agreement with experimental data, indicating that this process can dominate singlet fission in crystalline pentacene. Our approach is general and provides a framework for predicting and understanding multiexciton interactions in solids.

    View details for DOI 10.1103/PhysRevLett.119.267401

    View details for Web of Science ID 000418661700004

    View details for PubMedID 29328724

  • Environmental Screening Effects in 2D Materials: Renormalization of the Bandgap, Electronic Structure, and Optical Spectra, of Few-Layer Black Phosphorus NANO LETTERS Qiu, D. Y., da Jornada, F. H., Louie, S. G. 2017; 17 (8): 4706–12


    Few-layer black phosphorus has recently emerged as a promising 2D semiconductor, notable for its widely tunable bandgap, highly anisotropic properties, and theoretically predicted large exciton binding energies. To avoid degradation, it has become common practice to encapsulate black phosphorus devices. It is generally assumed that this encapsulation does not qualitatively affect their optical properties. Here, we show that the contrary is true. We have performed ab initio GW and GW plus Bethe-Salpeter equation (GW-BSE) calculations to determine the quasiparticle (QP) band structure and optical spectrum of one-layer (1L) through four-layer (4L) black phosphorus, with and without encapsulation between hexagonal boron nitride and sapphire. We show that black phosphorus is exceptionally sensitive to environmental screening. Encapsulation reduces the exciton binding energy in 1L by as much as 70% and completely eliminates the presence of a bound exciton in the 4L structure. The reduction in the exciton binding energies is offset by a similarly large renormalization of the QP bandgap so that the optical gap remains nearly unchanged, but the nature of the excited states and the qualitative features of the absorption spectrum change dramatically.

    View details for DOI 10.1021/acs.nanolett.7b01365

    View details for Web of Science ID 000407540300023

    View details for PubMedID 28677398

  • Optical Spectrum of MoS2: Many-Body Effects and Diversity of Exciton States PHYSICAL REVIEW LETTERS Qiu, D. Y., da Jornada, F. H., Louie, S. G. 2013; 111 (21): 216805


    We present first-principles calculations of the optical response of monolayer molybdenum disulfide employing the GW-Bethe-Salpeter equation (GW-BSE) approach including self-energy, excitonic, and electron-phonon effects. We show that monolayer MoS2 possesses a large and diverse number of strongly bound excitonic states with novel k-space characteristics that were not previously seen experimentally or theoretically. The absorption spectrum is shown to be dominated by excitonic states with a binding energy close to 1 eV and by strong electron-phonon broadening in the visible to ultraviolet range. Our results explain recent experimental measurements and resolve inconsistencies between previous GW-BSE calculations.

    View details for DOI 10.1103/PhysRevLett.111.216805

    View details for Web of Science ID 000327245900016

    View details for PubMedID 24313514

  • Multi-Objective Optimization for Rapid Identification of Novel Compound Metals for Interconnect Applications. Small (Weinheim an der Bergstrasse, Germany) Ramdas, A., Zhou, G., Li, Y., Lu, P. L., Antoniuk, E. R., Reed, E. J., Hinkle, C. L., da Jornada, F. H. 2024: e2308784


    Interconnect materials play the critical role of routing energy and information in integrated circuits. However, established bulk conductors, such as copper, perform poorly when scaled down beyond 10 nm, limiting the scalability of logic devices. Here, a multi-objective search is developed, combined with first-principles calculations, to rapidly screen over 15,000 materials and discover new interconnect candidates. This approach simultaneously optimizes the bulk electronic conductivity, surface scattering time, and chemical stability using physically motivated surrogate properties accessible from materials databases. Promising local interconnects are identified that have the potential to outperform ruthenium, the current state-of-the-art post-Cu material, and also semi-global interconnects with potentially large skin depths at the GHz operation frequency. The approach is validated on one of the identified candidates, CoPt, using both ab initio and experimental transport studies, showcasing its potential to supplant Ru and Cu for future local interconnects.

    View details for DOI 10.1002/smll.202308784

    View details for PubMedID 38593360

  • Imaging moiré excited states with photocurrent tunnelling microscopy. Nature materials Li, H., Xiang, Z., Naik, M. H., Kim, W., Li, Z., Sailus, R., Banerjee, R., Taniguchi, T., Watanabe, K., Tongay, S., Zettl, A., da Jornada, F. H., Louie, S. G., Crommie, M. F., Wang, F. 2024


    Moiré superlattices provide a highly tuneable and versatile platform to explore novel quantum phases and exotic excited states ranging from correlated insulators to moiré excitons. Scanning tunnelling microscopy has played a key role in probing microscopic behaviours of the moiré correlated ground states at the atomic scale. However, imaging of quantum excited states in moiré heterostructures remains an outstanding challenge. Here we develop a photocurrent tunnelling microscopy technique that combines laser excitation and scanning tunnelling spectroscopy to directly visualize the electron and hole distribution within the photoexcited moiré exciton in twisted bilayer WS2. The tunnelling photocurrent alternates between positive and negative polarities at different locations within a single moiré unit cell. This alternating photocurrent originates from the in-plane charge transfer moiré exciton in twisted bilayer WS2, predicted by our GW-Bethe-Salpeter equation calculations, that emerges from the competition between the electron-hole Coulomb interaction and the moiré potential landscape. Our technique enables the exploration of photoexcited non-equilibrium moiré phenomena at the atomic scale.

    View details for DOI 10.1038/s41563-023-01753-4

    View details for PubMedID 38172545

  • Importance of nonuniform Brillouin zone sampling for<i> ab</i><i> initio</i> Bethe-Salpeter equation calculations of exciton binding energies in crystalline solids PHYSICAL REVIEW B Alvertis, A. M., Champagne, A., Del Ben, M., da Jornada, F. H., Qiu, D. Y., Filip, M. R., Neaton, J. B. 2023; 108 (23)
  • Nanoscale and ultrafast <i>in situ</i> techniques to probe plasmon photocatalysis CHEMICAL PHYSICS REVIEWS Carlin, C. C., Dai, A. X., Al-Zubeidi, A., Simmerman, E. M., Oh, H., Gross, N., Lee, S. A., Link, S., Landes, C. F., da Jornada, F. H., Dionne, J. A. 2023; 4 (4)

    View details for DOI 10.1063/5.0163354

    View details for Web of Science ID 001112242700001

  • Machine-Learning-Driven Expansion of the 1D van der Waals Materials Space JOURNAL OF PHYSICAL CHEMISTRY C Zhu, Y., Antoniuk, E. R., Wright, D., Kargar, F., Sesing, N., Sendek, A. D., Salguero, T. T., Bartels, L., Balandin, A. A., Reed, E. J., da Jornada, F. H. 2023
  • Edge-Confined Excitons in Monolayer Black Phosphorus. ACS nano Biswas, S., Wong, J., Pokawanvit, S., Yang, W. D., Zhang, H., Akbari, H., Watanabe, K., Taniguchi, T., Davydov, A. V., da Jornada, F. H., Atwater, H. A. 2023


    Quantum confinement of two-dimensional excitons in van der Waals materials via electrostatic trapping, lithographic patterning, Moiré potentials, and chemical implantation has enabled significant advances in tailoring light emission from nanostructures. While such approaches rely on complex preparation of materials, natural edges are a ubiquitous feature in layered materials and provide a different approach for investigating quantum-confined excitons. Here, we observe that certain edge sites of monolayer black phosphorus (BP) strongly localize the intrinsic quasi-one-dimensional excitons, yielding sharp spectral lines in photoluminescence, with nearly an order of magnitude line width reduction. Through structural characterization of BP edges using transmission electron microscopy and first-principles GW plus Bethe-Salpeter equation (GW-BSE) calculations of exemplary BP nanoribbons, we find that certain atomic reconstructions can strongly quantum-confine excitons resulting in distinct emission features, mediated by local strain and screening. We observe linearly polarized luminescence emission from edge reconstructions that preserve the mirror symmetry of the parent BP lattice, in agreement with calculations. Furthermore, we demonstrate efficient electrical switching of localized edge excitonic luminescence, whose sites act as excitonic transistors for emission. Localized emission from BP edges motivates exploration of nanoribbons and quantum dots as hosts for tunable narrowband light generation, with future potential to create atomic-like structures for quantum information processing applications as well as exploration of exotic phases that may reside in atomic edge structures.

    View details for DOI 10.1021/acsnano.3c07337

    View details for PubMedID 37861986

  • Maximally localized exciton Wannier functions for solids PHYSICAL REVIEW B Haber, J. B., Qiu, D. Y., da Jornada, F. H., Neaton, J. B. 2023; 108 (12)
  • Emergent layer stacking arrangements in c-axis confined MoTe2. Nature communications Hart, J. L., Bhatt, L., Zhu, Y., Han, M. G., Bianco, E., Li, S., Hynek, D. J., Schneeloch, J. A., Tao, Y., Louca, D., Guo, P., Zhu, Y., Jornada, F., Reed, E. J., Kourkoutis, L. F., Cha, J. J. 2023; 14 (1): 4803


    The layer stacking order in 2D materials strongly affects functional properties and holds promise for next-generation electronic devices. In bulk, octahedral MoTe2 possesses two stacking arrangements, the ferroelectric Weyl semimetal Td phase and the higher-order topological insulator 1T' phase. However, in thin flakes of MoTe2, it is unclear if the layer stacking follows the Td, 1T', or an alternative stacking sequence. Here, we use atomic-resolution scanning transmission electron microscopy to directly visualize the MoTe2 layer stacking. In thin flakes, we observe highly disordered stacking, with nanoscale 1T' and Td domains, as well as alternative stacking arrangements not found in the bulk. We attribute these findings to intrinsic confinement effects on the MoTe2 stacking-dependent free energy. Our results are important for the understanding of exotic physics displayed in MoTe2 flakes. More broadly, this work suggests c-axis confinement as a method to influence layer stacking in other 2D materials.

    View details for DOI 10.1038/s41467-023-40528-y

    View details for PubMedID 37558697

    View details for PubMedCentralID 8024290

  • Giant self-driven exciton-Floquet signatures in time-resolved photoemission spectroscopy of MoS2 from time-dependent GW approach. Proceedings of the National Academy of Sciences of the United States of America Chan, Y. H., Qiu, D. Y., da Jornada, F. H., Louie, S. G. 2023; 120 (32): e2301957120


    Time-resolved, angle-resolved photoemission spectroscopy (TR-ARPES) is a one-particle spectroscopic technique that can probe excitons (two-particle excitations) in momentum space. We present an ab initio, time-domain GW approach to TR-ARPES and apply it to monolayer MoS2. We show that photoexcited excitons may be measured and quantified as satellite bands and lead to the renormalization of the quasiparticle bands. These features are explained in terms of an exciton-Floquet phenomenon induced by an exciton time-dependent bosonic field, which are orders of magnitude stronger than those of laser field-induced Floquet bands in low-dimensional semiconductors. Our findings imply a way to engineer Floquet matter through the coherent oscillation of excitons and open the new door for mechanisms for band structure engineering.

    View details for DOI 10.1073/pnas.2301957120

    View details for PubMedID 37523533

  • Spatially Resolved Moiré Excitons Fine Structure Using Cryogenic Low-loss EELS. Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada Sankar, S., Hays, P., Dandu, M., Naik, M. H., Barre, E., Taniguchi, T., Watanabe, K., Louie, S., da Jornada, F., Tongay, S., Hachtel, J., Ercius, P., Raja, A., Susarla, S. 2023; 29 (Supplement_1): 1716-1717

    View details for DOI 10.1093/micmic/ozad067.887

    View details for PubMedID 37613905

  • Sustainable chemistry with plasmonic photocatalysts NANOPHOTONICS Yuan, L., Bourgeois, B. B., Carlin, C. C., da Jornada, F. H., Dionne, J. A. 2023
  • Quasiparticle and Optical Properties of Carrier-Doped Monolayer MoTe2 from First Principles. Nano letters Champagne, A., Haber, J. B., Pokawanvit, S., Qiu, D. Y., Biswas, S., Atwater, H. A., da Jornada, F. H., Neaton, J. B. 2023


    The intrinsic weak and highly nonlocal dielectric screening of two-dimensional materials is well-known to lead to high sensitivity of their optoelectronic properties to environment. Less studied theoretically is the role of free carriers in those properties. Here, we use ab initio GW and Bethe-Salpeter equation calculations, with a rigorous treatment of dynamical screening and local-field effects, to study the doping dependence of the quasiparticle and optical properties of a monolayer transition-metal dichalcogenide, 2H MoTe2. We predict a quasiparticle band gap renormalization of several hundreds of meV for experimentally attainable carrier densities and a similarly sizable decrease in the exciton binding energy. This results in an almost constant excitation energy for the lowest-energy exciton resonance with an increasing doping density. Using a newly developed and generally applicable plasmon-pole model and a self-consistent solution of the Bethe-Salpeter equation, we reveal the importance of accurately capturing both dynamical and local-field effects to understand detailed photoluminescence measurements.

    View details for DOI 10.1021/acs.nanolett.3c00386

    View details for PubMedID 37159934

  • Exciton Lifetime and Optical Line Width Profile via Exciton-Phonon Interactions: Theory and First-Principles Calculations for Monolayer MoS2. Nano letters Chan, Y., Haber, J. B., Naik, M. H., Neaton, J. B., Qiu, D. Y., da Jornada, F. H., Louie, S. G. 2023


    Exciton dynamics dictates the evolution of photoexcited carriers in photovoltaic and optoelectronic devices. However, interpreting their experimental signatures is a challenging theoretical problem due to the presence of both electron-phonon and many-electron interactions. We develop and apply here a first-principles approach to exciton dynamics resulting from exciton-phonon coupling in monolayer MoS2 and reveal the highly selective nature of exciton-phonon coupling due to the internal spin structure of excitons, which leads to a surprisingly long lifetime of the lowest-energy bright A exciton. Moreover, we show that optical absorption processes rigorously require a second-order perturbation theory approach, with photon and phonon treated on an equal footing, as proposed by Toyozawa and Hopfield. Such a treatment, thus far neglected in first-principles studies, gives rise to off-diagonal exciton-phonon self-energy, which is critical for the description of dephasing mechanisms and yields exciton line widths in excellent agreement with experiment.

    View details for DOI 10.1021/acs.nanolett.3c00732

    View details for PubMedID 37071728

  • Rydberg Excitons and Trions in Monolayer MoTe2. ACS nano Biswas, S., Champagne, A., Haber, J. B., Pokawanvit, S., Wong, J., Akbari, H., Krylyuk, S., Watanabe, K., Taniguchi, T., Davydov, A. V., Al Balushi, Z. Y., Qiu, D. Y., da Jornada, F. H., Neaton, J. B., Atwater, H. A. 2023


    Monolayer transition metal dichalcogenide (TMDC) semiconductors exhibit strong excitonic optical resonances, which serve as a microscopic, noninvasive probe into their fundamental properties. Like the hydrogen atom, such excitons can exhibit an entire Rydberg series of resonances. Excitons have been extensively studied in most TMDCs (MoS2, MoSe2, WS2, and WSe2), but detailed exploration of excitonic phenomena has been lacking in the important TMDC material molybdenum ditelluride (MoTe2). Here, we report an experimental investigation of excitonic luminescence properties of monolayer MoTe2 to understand the excitonic Rydberg series, up to 3s. We report a significant modification of emission energies with temperature (4 to 300 K), thereby quantifying the exciton-phonon coupling. Furthermore, we observe a strongly gate-tunable exciton-trion interplay for all the Rydberg states governed mainly by free-carrier screening, Pauli blocking, and band gap renormalization in agreement with the results of first-principles GW plus Bethe-Salpeter equation approach calculations. Our results help bring monolayer MoTe2 closer to its potential applications in near-infrared optoelectronics and photonic devices.

    View details for DOI 10.1021/acsnano.3c00145

    View details for PubMedID 37043483

  • Analyzing and predicting non-equilibrium many-body dynamics via dynamic mode decomposition JOURNAL OF COMPUTATIONAL PHYSICS Yin, J., Chan, Y., da Jornada, F. H., Qiu, D. Y., Yang, C., Louie, S. G. 2023; 477
  • Hyperspectral imaging of exciton confinement within a moire unit cell with a subnanometer electron probe. Science (New York, N.Y.) Susarla, S., Naik, M. H., Blach, D. D., Zipfel, J., Taniguchi, T., Watanabe, K., Huang, L., Ramesh, R., da Jornada, F. H., Louie, S. G., Ercius, P., Raja, A. 2022; 378 (6625): 1235-1239


    Electronic and optical excitations in two-dimensional systems are distinctly sensitive to the presence of a moire superlattice. We used cryogenic transmission electron microscopy and spectroscopy to simultaneously image the structural reconstruction and associated localization of the lowest-energy intralayer exciton in a rotationally aligned WS2-WSe2 moire superlattice. In conjunction with optical spectroscopy and ab initio calculations, we determined that the exciton center-of-mass wave function is confined to a radius of approximately 2 nanometers around the highest-energy stacking site in the moire unit cell. Our results provide direct evidence that atomic reconstructions lead to the strongly confining moire potentials and that engineering strain at the nanoscale will enable new types of excitonic lattices.

    View details for DOI 10.1126/science.add9294

    View details for PubMedID 36520893

  • Elemental excitations in MoI3 one-dimensional van der Waals nanowires APPLIED PHYSICS LETTERS Kargar, F., Barani, Z., Sesing, N. R., Mai, T. T., Debnath, T., Zhang, H., Liu, Y., Zhu, Y., Ghosh, S., Biacchi, A. J., da Jornada, F. H., Bartels, L., Adel, T., Walker, A. R., Davydov, A. V., Salguero, T. T., Lake, R. K., Balandin, A. A. 2022; 121 (22)

    View details for DOI 10.1063/5.0129904

    View details for Web of Science ID 000891200900008

  • Using dynamic mode decomposition to predict the dynamics of a two-time non-equilibrium Green's function JOURNAL OF COMPUTATIONAL SCIENCE Yin, J., Chan, Y., da Jornada, F. H., Qiu, D. Y., Louie, S. G., Yang, C. 2022; 64
  • Intralayer charge-transfer moire excitons in van der Waals superlattices. Nature Naik, M. H., Regan, E. C., Zhang, Z., Chan, Y., Li, Z., Wang, D., Yoon, Y., Ong, C. S., Zhao, W., Zhao, S., Utama, M. I., Gao, B., Wei, X., Sayyad, M., Yumigeta, K., Watanabe, K., Taniguchi, T., Tongay, S., da Jornada, F. H., Wang, F., Louie, S. G. 2022; 609 (7925): 52-57


    Moire patterns of transition metal dichalcogenide heterobilayers have proved to be an ideal platform on which to host unusual correlated electronic phases, emerging magnetism and correlated exciton physics. Whereas the existence of new moire excitonic states is established1-4 through optical measurements, the microscopic nature of these states is still poorly understood, often relying on empirically fit models. Here, combining large-scale first-principles GW (where G and W denote the one-particle Green's function and the screened Coulomb interaction, respectively) plus Bethe-Salpeter calculations and micro-reflection spectroscopy, we identify the nature of the exciton resonances in WSe2/WS2 moire superlattices, discovering a rich set of moire excitons that cannot be captured by prevailing continuum models. Our calculations show moire excitons with distinct characters, including modulated Wannier excitons and previously unidentified intralayer charge-transfer excitons. Signatures of these distinct excitonic characters are confirmed experimentally by the unique carrier-density and magnetic-field dependences of different moire exciton resonances. Our study highlights the highly non-trivial exciton states that can emerge in transition metal dichalcogenide moire superlattices, and suggests new ways of tuning many-body physics in moire systems by engineering excited-states with specific spatial characters.

    View details for DOI 10.1038/s41586-022-04991-9

    View details for PubMedID 36045239

  • Quasiparticle energies and optical excitations of 3C-SiC divacancy from GW and GW plus Bethe-Salpeter equation calculations PHYSICAL REVIEW MATERIALS Gao, W., da Jornada, F. H., Del Ben, M., Deslippe, J., Louie, S. G., Chelikowsky, J. R. 2022; 6 (3)
  • Identifying Hidden Intracell Symmetries in Molecular Crystals and Their Impact for Multiexciton Generation. The journal of physical chemistry letters Altman, A. R., Refaely-Abramson, S., da Jornada, F. H. 1800: 747-753


    Organic molecular crystals are appealing for next-generation optoelectronic applications due to their multiexciton generation processes that can increase the efficiency of photovoltaic devices. However, a general understanding of how crystal structures affect these processes is lacking, requiring computationally demanding calculations for each material. Here we present an approach to understand and classify organic crystals and elucidate multiexciton processes. We show that organic crystals that are composed of two sublattices are well-approximated by effective fictitious systems of higher translational symmetry. Within this framework, we derive hidden selection rules in crystal pentacene and predict that the bulk polymorph supports fast Coulomb-mediated singlet fission with a transition rate about 2 orders of magnitude faster than that of the thin-film polymorph, a result confirmed with many-body perturbation theory calculations. Our approach is based on density-functional theory calculations and provides design principles for the experimental and computational discovery of new materials with tailored excitonic properties.

    View details for DOI 10.1021/acs.jpclett.1c03540

    View details for PubMedID 35029407

  • Discovering and understanding materials through computation. Nature materials Louie, S. G., Chan, Y., da Jornada, F. H., Li, Z., Qiu, D. Y. 2021; 20 (6): 728-735


    Materials modelling and design using computational quantum and classical approaches is by now well established as an essential pillar in condensed matter physics, chemistry and materials science research, in addition to experiments and analytical theories. The past few decades have witnessed tremendous advances in methodology development and applications to understand and predict the ground-state, excited-state and dynamical properties of materials, ranging from molecules to nanoscopic/mesoscopic materials to bulk and reduced-dimensional systems. This issue of Nature Materials presents four in-depth Review Articles on the field. This Perspective aims to give a brief overview of the progress, as well as provide some comments on future challenges and opportunities. We envision that increasingly powerful and versatile computational approaches, coupled with new conceptual understandings and the growth of techniques such as machine learning, will play a guiding role in the future search and discovery of materials for science and technology.

    View details for DOI 10.1038/s41563-021-01015-1

    View details for PubMedID 34045702

  • The 2021 Ultrafast Spectroscopic Probes of Condensed Matter Roadmap. Journal of physics. Condensed matter : an Institute of Physics journal Lloyd-Hughes, J., Oppeneer, P., Pereira Dos Santos, T., Schleife, A., Meng, S., Sentef, M. A., Ruggenthaler, M., Rubio, A., Radu, I., Murnane, M., Shi, X., Kapteyn, H., Stadtmuller, B., Dani, K. M., da Jornada, F., Prinz, E., Aeschlimann, M., Milot, R., Burdanova, M., Boland, J., Cocker, T. L., Hegmann, F. A. 2021


    In the 60 years since the invention of the laser, the scientific community has developed numerous fields of research based on these bright, coherent light sources, including the areas of imaging, spectroscopy, materials processing and communications. Ultrafast spectroscopy and imaging techniques are at the forefront of research into the light-matter interaction at the shortest times accessible to experiments, ranging from a few attoseconds to nanoseconds. Light pulses provide a crucial probe of the dynamical motion of charges, spins, and atoms on picosecond, femtosecond, and down to attosecond timescales, none of which are accessible even with the fastest electronic devices. Furthermore, strong light pulses can drive materials into unusual phases, with exotic properties. In this Roadmap we describe the current state-of-the-art in experimental and theoretical studies of condensed matter using ultrafast probes. In each contribution, the authors also use their extensive knowledge to highlight challenges and predict future trends.

    View details for DOI 10.1088/1361-648X/abfe21

    View details for PubMedID 33951618

  • Solving the Bethe-Salpeter equation on a subspace: Approximations and consequences for low-dimensional materials PHYSICAL REVIEW B Qiu, D. Y., da Jornada, F. H., Louie, S. G. 2021; 103 (4)
  • Directly visualization of excitonic wavefunction in 2D semiconductors by angle resolved photoemission spectroscopy Man, M. L., Madeo, J., Sahoo, C., Xie, K., Campbell, M., Pareek, V., Karmakar, A., Wong, E., Al-Mahboob, A., Chan, N. S., Bacon, D. R., Zhu, X., Abdelrasoul, M., Li, X., Heinz, T. F., da Jornada, F. H., Cao, T., Dani, K. M., IEEE IEEE. 2021
  • Reproducibility in G(0)W(0) calculations for solids COMPUTER PHYSICS COMMUNICATIONS Rangel, T., Del Ben, M., Varsano, D., Antonius, G., Bruneval, F., Jornada, F. H., van Setten, M. J., Orhan, O. K., O'Regan, D. D., Canning, A., Ferretti, A., Marini, A., Rignanese, G., Deslippe, J., Louie, S. G., Neaton, J. B. 2020; 255
  • Accelerating Large-Scale Excited-State GW Calculations on Leadership HPC Systems SC20 Del Ben, M., Yang, C., Li, Z., da Jornada, F. H., Louie, S. G., Deslippe, J. 2020: 11
  • Accelerating GW-Based Energy Level Alignment Calculations for Molecule-Metal Interfaces Using a Substrate Screening Approach JOURNAL OF CHEMICAL THEORY AND COMPUTATION Liu, Z., da Jornada, F. H., Louie, S. G., Neaton, J. B. 2019; 15 (7): 4218–27


    The physics of electronic energy level alignment at interfaces formed between molecules and metals can in general be accurately captured by the ab initio GW approach. However, the computational cost of such GW calculations for typical interfaces is significant, given their large system size and chemical complexity. In the past, approximate self-energy corrections, such as those constructed from image-charge models together with gas-phase molecular level corrections, have been used to compute level alignment with good accuracy. However, these approaches often neglect dynamical effects of the polarizability and require the definition of an image plane. In this work, we propose a new approximation to enable more efficient GW-quality calculations of interfaces, where we greatly simplify the calculation of the noninteracting polarizability, a primary bottleneck for large heterogeneous systems. This is achieved by first computing the noninteracting polarizability of each individual component of the interface, e.g., the molecule and the metal, without the use of large supercells, and then using folding and spatial truncation techniques to efficiently combine these quantities. Overall this approach significantly reduces the computational cost for conventional GW calculations of level alignment without sacrificing the accuracy. Moreover, this approach captures both dynamical and nonlocal polarization effects without the need to invoke a classical image-charge expression or to define an image plane. We demonstrate our approach by considering a model system of benzene at relatively low coverage on the aluminum (111) surface. Although developed for such interfaces, the method can be readily extended to other heterogeneous interfaces.

    View details for DOI 10.1021/acs.jctc.9b00326

    View details for Web of Science ID 000475409000028

    View details for PubMedID 31194538

  • Electron-Phonon Coupling from Ab Initio Linear-Response Theory within the GW Method: Correlation-Enhanced Interactions and Superconductivity in Ba1-xKxBiO3 PHYSICAL REVIEW LETTERS Li, Z., Antonius, G., Wu, M., da Jornada, F. H., Louie, S. G. 2019; 122 (18): 186402


    We present a new first-principles linear-response theory of changes due to perturbations in the quasiparticle self-energy operator within the GW method. This approach, named GW perturbation theory (GWPT), is applied to calculate the electron-phonon (e-ph) interactions with the full inclusion of the GW nonlocal, energy-dependent self-energy effects, going beyond density-functional perturbation theory. Avoiding limitations of the frozen-phonon technique, GWPT gives access to e-ph matrix elements at the GW level for all phonons and scattering processes, and the computational cost scales linearly with the number of phonon modes (wave vectors and branches) investigated. We demonstrate the capabilities of GWPT by studying the e-ph coupling and superconductivity in Ba_{0.6}K_{0.4}BiO_{3}. We show that many-electron correlations significantly enhance the e-ph interactions for states near the Fermi surface, and explain the observed high superconductivity transition temperature of Ba_{0.6}K_{0.4}BiO_{3} as well as its doping dependence.

    View details for DOI 10.1103/PhysRevLett.122.186402

    View details for Web of Science ID 000467739200010

    View details for PubMedID 31144877

  • Static subspace approximation for the evaluation of G(0)W(0) quasiparticle energies within a sum-over-bands approach PHYSICAL REVIEW B Del Ben, M., da Jornada, F. H., Antonius, G., Rangel, T., Louie, S. G., Deslippe, J., Canning, A. 2019; 99 (12)
  • A dielectric-defined lateral heterojunction in a monolayer semiconductor NATURE ELECTRONICS Utama, M., Kleemann, H., Zhao, W., Ong, C., da Jornada, F. H., Qiu, D. Y., Cai, H., Li, H., Kou, R., Zhao, S., Wang, S., Watanabe, K., Taniguchi, T., Tongay, S., Zettl, A., Louie, S. G., Wang, F. 2019; 2 (2): 60–65
  • Large-scale GW calculations on pre-exascale HPC systems COMPUTER PHYSICS COMMUNICATIONS Del Ben, M., da Jornada, F. H., Canning, A., Wichmann, N., Raman, K., Sasanka, R., Yang, C., Louie, S. G., Deslippe, J. 2019; 235: 187–95
  • Low-lying excited states in crystalline perylene PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Rangel, T., Rinn, A., Sharifzadeh, S., da Jornada, F. H., Pick, A., Louie, S. G., Witte, G., Kronik, L., Neaton, J. B., Chatterjee, S. 2018; 115 (2): 284–89


    Organic materials are promising candidates for advanced optoelectronics and are used in light-emitting diodes and photovoltaics. However, the underlying mechanisms allowing the formation of excited states responsible for device functionality, such as exciton generation and charge separation, are insufficiently understood. This is partly due to the wide range of existing crystalline polymorphs depending on sample preparation conditions. Here, we determine the linear optical response of thin-film single-crystal perylene samples of distinct polymorphs in transmission and reflection geometries. The sample quality allows for unprecedented high-resolution spectroscopy, which offers an ideal opportunity for judicious comparison between theory and experiment. Excellent agreement with first-principles calculations for the absorption based on the GW plus Bethe-Salpeter equation (GW-BSE) approach of many-body perturbation theory (MBPT) is obtained, from which a clear picture of the low-lying excitations in perylene emerges, including evidence of an exciton-polariton stopband, as well as an assessment of the commonly used Tamm-Dancoff approximation to the GW-BSE approach. Our findings on this well-controlled system can guide understanding and development of advanced molecular solids and functionalization for applications.

    View details for DOI 10.1073/pnas.1711126115

    View details for Web of Science ID 000419686400042

    View details for PubMedID 29279373

    View details for PubMedCentralID PMC5777036


    View details for DOI 10.1137/16M1102641

    View details for Web of Science ID 000436971900006

  • Accelerating Optical Absorption Spectra and Exciton Energy Computation via Interpolative Separable Density Fitting Hu, W., Shao, M., Cepellotti, A., da Jornada, F. H., Lin, L., Thicke, K., Yang, C., Louie, S. G., Shi, Y., Fu, H., Tian, Y., Krzhizhanovskaya, V. V., Lees, M. H., Dongarra, J., Sloot, P. M. SPRINGER INTERNATIONAL PUBLISHING AG. 2018: 604–17
  • Ab initio Modelling of Plasmons in Metal-semiconductor Bilayer Transition-metal Dichalcogenide Heterostructures ISRAEL JOURNAL OF CHEMISTRY Sener Sen, H., Xian, L., da Jornada, F. H., Louie, S. G., Rubio, A. 2017; 57 (6): 540–46
  • Nonuniform sampling schemes of the Brillouin zone for many-electron perturbation-theory calculations in reduced dimensionality PHYSICAL REVIEW B da Jornada, F. H., Qiu, D. Y., Louie, S. G. 2017; 95 (3)
  • Direct observation of the layer-dependent electronic structure in phosphorene NATURE NANOTECHNOLOGY Li, L., Kim, J., Jin, C., Ye, G., Qiu, D. Y., da Jornada, F. H., Shi, Z., Chen, L., Zhang, Z., Yang, F., Watanabe, K., Taniguchi, T., Ren, W., Louie, S. G., Chen, X., Zhang, Y., Wang, F. 2017; 12 (1): 21–25


    Phosphorene, a single atomic layer of black phosphorus, has recently emerged as a new two-dimensional (2D) material that holds promise for electronic and photonic technologies. Here we experimentally demonstrate that the electronic structure of few-layer phosphorene varies significantly with the number of layers, in good agreement with theoretical predictions. The interband optical transitions cover a wide, technologically important spectral range from the visible to the mid-infrared. In addition, we observe strong photoluminescence in few-layer phosphorene at energies that closely match the absorption edge, indicating that they are direct bandgap semiconductors. The strongly layer-dependent electronic structure of phosphorene, in combination with its high electrical mobility, gives it distinct advantages over other 2D materials in electronic and opto-electronic applications.

    View details for DOI 10.1038/NNANO.2016.171

    View details for Web of Science ID 000392042400008

    View details for PubMedID 27643457

  • Excitation spectra of aromatic molecules within a real-space GW-BSE formalism: Role of self-consistency and vertex corrections PHYSICAL REVIEW B Hung, L., da Jornada, F. H., Souto-Casares, J., Chelikowsky, J. R., Louie, S. G., Ogut, S. 2016; 94 (8)
  • Low rank approximation in G (0) W (0) calculations Shao MeiYue, Lin Lin, Yang Chao, Liu Fang, Da Jornada, F. H., Deslippe, J., Louie, S. G. SCIENCE PRESS. 2016: 1593–1612
  • Screening and many-body effects in two-dimensional crystals: Monolayer MoS2 PHYSICAL REVIEW B Qiu, D. Y., da Jornada, F. H., Louie, S. G. 2016; 93 (23)
  • Structure preserving parallel algorithms for solving the Bethe-Salpeter eigenvalue problem LINEAR ALGEBRA AND ITS APPLICATIONS Shao, M., da Jornada, F. H., Yang, C., Deslippe, J., Louie, S. G. 2016; 488: 148–67
  • Optimizing Excited-State Electronic-Structure Codes for Intel Knights Landing: A Case Study on the BerkeleyGW Software Deslippe, J., da Jornada, F. H., Vigil-Fowler, D., Barnes, T., Wichmann, N., Raman, K., Sasanka, R., Louie, S. G., Taufer, M., Mohr, B., Kunkel, J. M. SPRINGER INTERNATIONAL PUBLISHING AG. 2016: 402–14
  • Probing the Role of Interlayer Coupling and Coulomb Interactions on Electronic Structure in Few-Layer MoSe2 Nanostructures NANO LETTERS Bradley, A. J., Ugeda, M. M., da Jornada, F. H., Qiu, D. Y., Ruan, W., Zhang, Y., Wickenburg, S., Riss, A., Lu, J., Mo, S., Hussain, Z., Shen, Z., Louie, S. G., Crommie, M. F. 2015; 15 (4): 2594-2599


    Despite the weak nature of interlayer forces in transition metal dichalcogenide (TMD) materials, their properties are highly dependent on the number of layers in the few-layer two-dimensional (2D) limit. Here, we present a combined scanning tunneling microscopy/spectroscopy and GW theoretical study of the electronic structure of high quality single- and few-layer MoSe2 grown on bilayer graphene. We find that the electronic (quasiparticle) bandgap, a fundamental parameter for transport and optical phenomena, decreases by nearly one electronvolt when going from one layer to three due to interlayer coupling and screening effects. Our results paint a clear picture of the evolution of the electronic wave function hybridization in the valleys of both the valence and conduction bands as the number of layers is changed. This demonstrates the importance of layer number and electron-electron interactions on van der Waals heterostructures and helps to clarify how their electronic properties might be tuned in future 2D nanodevices.

    View details for DOI 10.1021/acs.nanolett.51300160

    View details for Web of Science ID 000352750200057

    View details for PubMedID 25775022

  • Numerical integration for ab initio many-electron self energy calculations within the GW approximation JOURNAL OF COMPUTATIONAL PHYSICS Liu, F., Lin, L., Vigil-Fowler, D., Lischner, J., Kemper, A. F., Sharifzadeh, S., da Jornadad, F. H., Deslippe, J., Yang, C., Neaton, J. B., Louie, S. G. 2015; 286: 1–13
  • Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor NATURE MATERIALS Ugeda, M. M., Bradley, A. J., Shi, S., da Jornada, F. H., Zhang, Y., Qiu, D. Y., Ruan, W., Mo, S., Hussain, Z., Shen, Z., Wang, F., Louie, S. G., Crommie, M. F. 2014; 13 (12): 1091-1095


    Two-dimensional (2D) transition metal dichalcogenides (TMDs) are emerging as a new platform for exploring 2D semiconductor physics. Reduced screening in two dimensions results in markedly enhanced electron-electron interactions, which have been predicted to generate giant bandgap renormalization and excitonic effects. Here we present a rigorous experimental observation of extraordinarily large exciton binding energy in a 2D semiconducting TMD. We determine the single-particle electronic bandgap of single-layer MoSe2 by means of scanning tunnelling spectroscopy (STS), as well as the two-particle exciton transition energy using photoluminescence (PL) spectroscopy. These yield an exciton binding energy of 0.55 eV for monolayer MoSe2 on graphene—orders of magnitude larger than what is seen in conventional 3D semiconductors and significantly higher than what we see for MoSe2 monolayers in more highly screening environments. This finding is corroborated by our ab initio GW and Bethe-Salpeter equation calculations which include electron correlation effects. The renormalized bandgap and large exciton binding observed here will have a profound impact on electronic and optoelectronic device technologies based on single-layer semiconducting TMDs.

    View details for DOI 10.1038/NMAT4061

    View details for Web of Science ID 000345432200009

  • Tuning Many-Body Interactions in Graphene: The Effects of Doping on Excitons and Carrier Lifetimes PHYSICAL REVIEW LETTERS Mak, K. F., da Jornada, F. H., He, K., Deslippe, J., Petrone, N., Hone, J., Shan, J., Louie, S. G., Heinz, T. F. 2014; 112 (20)
  • Modeling of amorphous carbon structures with arbitrary structural constraints JOURNAL OF PHYSICS-CONDENSED MATTER Jornada, F. H., Gava, V., Martinotto, A. L., Cassol, L. A., Perottoni, C. A. 2010; 22 (39): 395402


    In this paper we describe a method to generate amorphous structures with arbitrary structural constraints. This method employs the simulated annealing algorithm to minimize a simple yet carefully tailored cost function (CF). The cost function is composed of two parts: a simple harmonic approximation for the energy-related terms and a cost that penalizes configurations that do not have atoms in the desired coordinations. Using this approach, we generated a set of amorphous carbon structures spawning nearly all the possible combinations of sp, sp(2) and sp(3) hybridizations. The bulk moduli of this set of amorphous carbons structures was calculated using Brenner's potential. The bulk modulus strongly depends on the mean coordination, following a power-law behavior with an exponent ν = 1.51 ± 0.17. A modified cost function that segregates carbon with different hybridizations is also presented, and another set of structures was generated. With this new set of amorphous materials, the correlation between the bulk modulus and the mean coordination weakens. The method proposed can be easily modified to explore the effects on the physical properties of the presence of hydrogen, dangling bonds, and structural features such as carbon rings.

    View details for DOI 10.1088/0953-8984/22/39/395402

    View details for Web of Science ID 000281958500017

    View details for PubMedID 21403228