Ab Initio Quantum Ultrafast Dynamics of Electrons in Materials

The dynamics of excited electrons in materials at femtosecond to nanosecond time scales is central to applications ranging from hot-carrier photochemistry to spintronics and quantum information. Materials design to gainfully exploit this dynamics requires first-principles prediction of electron scattering by phonons, defects and other electrons. We will briefly review our long-standing effort to predict the ultrafast dynamics and nanoscale transport of hot carriers in plasmonic materials, as well as the collection of carriers across material interfaces. These simulations combine quantum-mechanical prediction of scattering rates with the semi-classical Boltzmann equation to efficiently access the large length and time scales relevant for hot carrier processes. However, such semi-classical approaches cannot address the dynamics of quantum degrees of freedom in materials, such as spin. Further, relevant time scales of excited spin dynamics in materials can exceed several nanoseconds, far beyond the reach of direct first-principles simulations.<br/>We present a Lindbladian density-matrix framework for <i>ab initio simulations</i> of quantum ultrafast dynamics that naturally incorporates both coherent and incoherent evolution of electrons, including scattering by phonons, defects and electrons. We demonstrate quantitative prediction of spin-phonon relaxation in a wide range of materials with varying dimensionality and symmetry, spanning completely different traditional mechanisms of spin relaxation. With graphene as an example, we show the transition from the Elliot-Yafet relaxation mechanism in inversion-symmetric materials to the Dyakonov-Perel relaxation mechanism when inversion symmetry is broken by electric fields and substrates. Finally, we showcase the power of this framework to directly simulate experimental probes of quantum dynamics in materials including ultrafast pump-probe, electron spin resonance and Hahn spin echo measurements, paving the way towards first-principles design of materials for quantum dynamics.<br/>This work was supported by the National Science Foundation under Award# 1956015.