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Report: Psi-K / CECAM workshop in Lugano on Electron-phonon coupling

Joint Psi-K / CECAM workshop: Electron-phonon coupling: Computational methods for electronic transport in nanostructures and in bulk materials
Dates: 14-16. October 2019
Location: USI Lugano, Switzerland

During 3 hectic days in October 2019, 25 researchers from different specialties meet in Lugano to discuss and learn about electron-phonon coupling. The purpose of the workshop was explicitly to foster collaboration between researchers in the following fields:

  • Real-life performance of semiconductors and metals, whether it be in one, two, or three dimensions, is often limited by carrier scattering by phonons. The mobility of charge carriers is a key parameter in the semiconductor industry to describe the electrical performance and the movement under applied electric fields. The traditional approach to calculate phonon-limited mobility is based on the Boltzmann transport equation in combination with the effective mass approximation and empirical deformation potentials. In recent years predictive parameter-free mobility calculations have been carried out at the density functional theory (DFT) level for the electron-phonon coupling (EPC).
  • EPC may also lead to a Bose-Einstein condensation of electrons near the Fermi surface as Cooper pairs, resulting in conventional superconductivity at sufficiently low temperatures or high pressures. Also here DFT calculations of EPC have explained the origin of superconductivity in a range of materials and provided quantitative estimates for the critical temperature using Migdal-Eliashberg theory. A recent example includes first-principles theory that revealed how high-pressure hydrogen sulfide is a strongly anharmonic superconductor.
  • In a different context, the introduction of Inelastic Electron Tunneling Spectroscopy have opened up the possibility to study adsorbates and molecular junctions and to characterize inelastic scattering against vibrations down to the single-molecule limit. Ab-initio approaches based on DFT and nonequilibrium Green’s functions (NEGF) have been developed to describe the EPC in such nanoscale junctions and to explain the inelastic transport characteristics.

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