Bio


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


  • 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)

2021-22 Courses


Stanford Advisees


All Publications


  • 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

    Abstract

    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

    Abstract

    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)

    Abstract

    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)

    Abstract

    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

    Abstract

    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

    Abstract

    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

    Abstract

    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

    Abstract

    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

  • 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

    Abstract

    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

    Abstract

    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

    Abstract

    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)
  • 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

    Abstract

    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

    Abstract

    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

    Abstract

    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

  • A STRUCTURE PRESERVING LANCZOS ALGORITHM FOR COMPUTING THE OPTICAL ABSORPTION SPECTRUM SIAM JOURNAL ON MATRIX ANALYSIS AND APPLICATIONS Shao, M., da Jornada, F. H., Lin, L., Yang, C., Deslippe, J., Louie, S. G. 2018; 39 (2): 683–711

    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

    Abstract

    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

    Abstract

    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

    Abstract

    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

    Abstract

    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