Driving collective current excitations using light

Project title: Driving collective current excitations using light
Main applicant: Chin Shen Ong, Materials Theory
Grant amount: SEK 4 800 000 for the period 2026-2029

Electron-electron interactions in solids typically lead to longitudinal collective charge excitations known as plasmons, observable as resonances in the electron density-density response. Using the non-equilibrium twotime GW approach to solve the Kadanoff-Baym equations for sodium metal, we show that current-current interactions give rise to a fundamentally new collective excitation: the curron. Unlike plasmons, currons stem from transverse, current-driven interactions explicitly coupled to vector potentials rather than scalar ones. This project formalizes currons theoretically, predicts their unique dynamical properties, and identifies clear experimental signatures observable through advanced spectroscopy.

Currons mark a paradigm shift in our understanding of collective excitations. Beyond their conceptual novelty, they enable direct manipulation and coherent control of electron currents on ultrafast timescales, independent of charge accumulation. This unlocks new possibilities for ultrafast optoelectronics, quantum coherent devices, and emergent quantum phenomena. To support this, we will develop and openly share UppsalaGW, a scalable software platform that empowers researchers to analyze ultrafast experiments and explore nonequilibrium physics with unprecedented precision.