Interlayer exciton dynamics in van der Waals heterostructures

Exciton binding energies of hundreds of meV and strong light absorption in the optical frequency range make transition metal dichalcogenides (TMDs) promising for novel optoelectronic nanodevices. In particular, atomically thin TMDs can be stacked to heterostructures enabling the design of new materials with tailored properties. The strong Coulomb interaction gives rise to interlayer excitons, where electrons and holes are spatially separated in different layers. In this work, we reveal the microscopic processes behind the formation, thermalization and decay of these fundamentally interesting and technologically relevant interlayer excitonic states. In particular, we present for the exemplar…

Kohn-Sham Decomposition in Real-Time Time-Dependent Density-Functional Theory An Efficient Tool for Analyzing Plasmonic Excitations

The real-time-propagation formulation of time-dependent density-functional theory (RT-TDDFT) is an efficient method for modeling the optical response of molecules and nanoparticles. Compared to the widely adopted linear-response TDDFT approaches based on, e.g., the Casida equations, RT-TDDFT appears, however, lacking efficient analysis methods. This applies in particular to a decomposition of the response in the basis of the underlying single-electron states. In this work, we overcome this limitation by developing an analysis method for obtaining the Kohn-Sham electron-hole decomposition in RT-TDDFT. We demonstrate the equivalence between the developed method and the Casida approach by a be…

Plasmon-Induced Direct Hot-Carrier Transfer at Metal-Acceptor Interfaces.

Plasmon-induced hot-carrier transfer from a metal nanostructure to an acceptor is known to occur via two key mechanisms: (i) indirect transfer, where the hot carriers are produced in the metal nanostructure and subsequently transferred to the acceptor, and (ii) direct transfer, where the plasmons decay by directly exciting carriers from the metal to the acceptor. Unfortunately, an atomic-level understanding of the direct-transfer process, especially with regard to its quantification, remains elusive even though it is estimated to be more efficient compared to the indirect-transfer process. This is due to experimental challenges in separating direct from indirect transfer as both processes o…

Ultrastrong Coupling of a Single Molecule to a Plasmonic Nanocavity: A First-Principles Study

| openaire: EC/H2020/838996/EU//RealNanoPlasmon Funding Information: We acknowledge financial support from the Swedish Research Council (VR Miljö, Grant No: 2016-06059), the Knut and Alice Wallenberg Foundation (Grant No: 2019.0140), the Polish National Science Center (projects 2019/34/E/ST3/00359 and 2019/35/B/ST5/02477). T.P.R. acknowledges support from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 838996 and support from the Academy of Finland under the Grant No. 332429. T.J.A. acknowledges support from the Project HPC-EUROPA3 (INFRAIA-2016-1-730897), with the support of the EC Research Innovation Action under the H…

Direct hot-carrier transfer in plasmonic catalysis

Plasmonic metal nanoparticles can concentrate optical energy and enhance chemical reactions on their surfaces. Plasmons can interact with adsorbate orbitals and decay by directly exciting a carrier from the metal to the adsorbate in a process termed the direct-transfer process. Although this process could be useful for enhancing the efficiency of a chemical reaction, it remains poorly understood. Here, we report a preliminary investigation employing time-dependent density-functional theory (TDDFT) calculations to capture this process at a model metal-adsorbate interface formed by a silver nanoparticle (Ag147) and a carbon monoxide molecule (CO). Direct hot-electron transfer is observed to o…

Interlayer exciton dynamics in van der Waals heterostructures

Atomically thin transition metal dichalcogenides can be stacked to van der Waals heterostructures enabling the design of new materials with tailored properties. The strong Coulomb interaction gives rise to interlayer excitons, where electrons and holes are spatially separated in different layers. In this work, we reveal the time- and momentum-dependent elementary processes behind the formation, thermalization and photoemission of interlayer excitons for the exemplary MoSe2–WSe2 heterostructure. We identify tunneling of holes from MoSe2 to WSe2 on a ps timescale as the crucial process for interlayer exciton formation. We also predict a drastic reduction of the formation time as a function of…

Electric Field-Induced Surface Melting of Gold Observed In Situ at Room Temperature and at Atomic Resolution Using TEM

libvdwxc: A library for exchange-correlation functionals in the vdW-DF family

We present libvdwxc, a general library for evaluating the energy and potential for the family of vdW-DF exchange--correlation functionals. libvdwxc provides an efficient implementation of the vdW-DF method and can be interfaced with various general-purpose DFT codes. Currently, the GPAW and Octopus codes implement interfaces to libvdwxc. The present implementation emphasizes scalability and parallel performance, and thereby enables \textit{ab initio} calculations of nanometer-scale complexes. The numerical accuracy is benchmarked on the S22 test set whereas parallel performance is benchmarked on ligand-protected gold nanoparticles ($\text{Au}_{144}(\text{SC}_{11}\text{NH}_{25})_{60}$) up to…

Hot-Carrier Generation in Plasmonic Nanoparticles: The Importance of Atomic Structure

Metal nanoparticles are attractive for plasmon-enhanced generation of hot carriers, which may be harnessed in photochemical reactions. In this work, we analyze the coherent femtosecond dynamics of photon absorption, plasmon formation, and subsequent hot-carrier generation through plasmon dephasing using first-principles simulations. We predict the energetic and spatial hot-carrier distributions in small metal nanoparticles and show that the distribution of hot electrons is very sensitive to the local structure. Our results show that surface sites exhibit enhanced hot-electron generation in comparison to the bulk of the nanoparticle. While the details of the distribution depend on particle s…

Dipolar coupling of nanoparticle-molecule assemblies: An efficient approach for studying strong coupling

Strong light-matter interactions facilitate not only emerging applications in quantum and non-linear optics but also modifications of materials properties. In particular the latter possibility has spurred the development of advanced theoretical techniques that can accurately capture both quantum optical and quantum chemical degrees of freedom. These methods are, however, computationally very demanding, which limits their application range. Here, we demonstrate that the optical spectra of nanoparticle-molecule assemblies, including strong coupling effects, can be predicted with good accuracy using a subsystem approach, in which the response functions of the different units are coupled only a…

Electric-field-controlled reversible order-disorder switching of a metal tip surface

While it is well established that elevated temperatures can induce surface roughening of metal surfaces, the effect of a high electric field on the atomic structure at ambient temperature has not been investigated in detail. Here we show with atomic resolution using in situ transmission electron microscopy how intense electric fields induce reversible switching between perfect crystalline and disordered phases of gold surfaces at room temperature. Ab initio molecular dynamics simulations reveal that the mechanism behind the structural change can be attributed to a vanishing energy cost in forming surface defects in high electric fields. Our results demonstrate how surface processes can be d…

Data for "Hot-Carrier Generation in Plasmonic Nanoparticles: The Importance of Atomic Structure"

This upload includes the data presented and analyzed in the article "Hot-Carrier Generation in Plasmonic Nanoparticles: The Importance of Atomic Structure" by Tuomas P. Rossi, Paul Erhart, and Mikael Kuisma. The codes for reproducing the data are provided at doi:10.5281/zenodo.3964229. See README.md in data.zip for a detailed description.

Data and code for "Dipolar coupling of nanoparticle-molecule assemblies: An efficient approach for studying strong coupling"

The data includes the optical excitations of benzene, the optical spectra of coupled benzene-Al NP systems, and fits of the spectra to the coupled oscillator model. The optical spectra in question have been obtained in the dipolar coupling approximation and analyzed in the article "Dipolar coupling of nanoparticle-molecule assemblies: An efficient approach for studying strong coupling" by Jakub Fojt, Tuomas P. Rossi, Tomasz J. Antosiewicz, Mikael Kuisma and Paul Erhart. Scripts for processing of the data, which extract optical spectra from NWChem output files, and fit optical spectra to the coupled oscillator model, are also included. The scripts are written in Python and require …