Samuel Poncé | EPFL Graph Search

Professional employment Marie Skłodowska-Curie Individual FellowNovember 2019 - presentAdvisor: Prof. Nicola MarzariSTI IMX THEOS, École Polytechnique Fédérale de Lausanne, SwitzerlandJunior Research FellowJanuary 2016 - January 2022Wolfson College, University of Oxford, United Kingdom Postdoctoral Research AssistantMay 2015 - October 2019Advisor: Prof. Feliciano GiustinoDepartment of Materials, University of Oxford, United Kingdom Education Ph.D. Solid State PhysicsSeptember 2010 - January 2015Advisor: Prof. Xavier GonzeThesis: First-Principles Study of Phosphors for White LEDs Applications and of the Temperature Dependence of the Electronic StructureÉcole polytechnique de Louvain, Université catholique de Louvain, BelgiumM.A. Civil Engineer in Chemistry and Material ScienceSeptember 2008 - June 2010École polytechnique de Louvain, Université catholique de Louvain, BelgiumB.A. Civil EngineerSeptember 2005 - June 2008École polytechnique de Louvain, Université catholique de Louvain, Belgium

Long-range electrostatic contribution to electron-phonon couplings and mobilities of two-dimensional and bulk materials

Marco Gibertini, Nicola Marzari, Samuel Poncé, Massimiliano Stengel

Charge transport plays a crucial role in manifold potential applications of two-dimensional materials, in-cluding field-effect transistors, solar cells, and transparent conductors. At most operating temperatures, charge transport is hindered by scattering of carriers by lattice vibrations. Assessing the intrinsic phonon-limited carrier mobility is thus of paramount importance to identify promising candidates for next-generation devices. Here we provide a framework to efficiently compute the drift and Hall carrier mobility of two-dimensional materials through the Boltzmann transport equation by relying on a Fourier-Wannier interpolation. Building on a recent formulation of long-range contributions to dynamical matrices and phonon dispersions [Phys. Rev. X 11, 041027 (2021)], we extend the approach to electron-phonon coupling including the effect of dynamical dipoles and quadrupoles. We identify an unprecedented contribution associated with the Berry connection that is crucial to preserve the Wannier-gauge covariance of the theory. This contribution is not specific to two-dimensional crystals, but also concerns the three-dimensional case, as we demonstrate via an application to bulk SrO. We showcase our method on a wide selection of relevant monolayers ranging from SnS2 to MoS2, graphene, BN, InSe, and phosphorene. We also discover a nontrivial temperature evolution of the Hall hole mobility in InSe whereby the mobility increases with temperature above 150 K due to the Mexican-hat electronic structure of the InSe valence bands. Overall, we find that dynamical quadrupoles are essential and can impact the carrier mobility in excess of 75%.

AMER PHYSICAL SOC2023

General invariance and equilibrium conditions for lattice dynamics in 1D, 2D, and 3D materials

Changpeng Lin, Nicola Marzari, Samuel Poncé

The long-wavelength behavior of vibrational modes plays a central role in carrier transport, phonon-assisted optical properties, superconductivity, and thermomechanical and thermoelectric properties of materials. Here, we present general invariance and equilibrium conditions of the lattice potential; these allow to recover the quadratic dispersions of flexural phonons in low-dimensional materials, in agreement with the phenomenological model for long-wavelength bending modes. We also prove that for any low-dimensional material the bending modes can have a purely out-of-plane polarization in the vacuum direction and a quadratic dispersion in the long-wavelength limit. In addition, we propose an effective approach to treat invariance conditions in crystals with non-vanishing Born effective charges where the long-range dipole-dipole interactions induce a contribution to the lattice potential and stress tensor. Our approach is successfully applied to the phonon dispersions of 158 two-dimensional materials, highlighting its critical relevance in the study of phonon-mediated properties of low-dimensional materials.

NATURE PORTFOLIO2022

Common workflows for computing material properties using different quantum engines

Marnik Bercx, Kristjan Eimre, Sebastiaan Philippe Huber, Conrad Johnston, Nicola Marzari, Giovanni Pizzi, Samuel Poncé, Gian-Marco Rignanese, Christopher John Sewell, Berend Smit, Martin Uhrin, Aliaksandr Yakutovich, Austin Jacob Zadoks

The prediction of material properties based on density-functional theory has become routinely common, thanks, in part, to the steady increase in the number and robustness of available simulation packages. This plurality of codes and methods is both a boon and a burden. While providing great opportunities for cross-verification, these packages adopt different methods, algorithms, and paradigms, making it challenging to choose, master, and efficiently use them. We demonstrate how developing common interfaces for workflows that automatically compute material properties greatly simplifies interoperability and cross-verification. We introduce design rules for reusable, code-agnostic, workflow interfaces to compute well-defined material properties, which we implement for eleven quantum engines and use to compute various material properties. Each implementation encodes carefully selected simulation parameters and workflow logic, making the implementer’s expertise of the quantum engine directly available to non-experts. All workflows are made available as open-source and full reproducibility of the workflows is guaranteed through the use of the AiiDA infrastructure.

2021