Numerical Simulation of Strain Variations in Graphene

Graphene is a highly promising material for a variety of applications, and in many of those, defects, strain, and strain variations can play a fundamental role in the material properties and resulting device performance. Here we present our group’s use of numerical simulations to examine the role of defects and strain variations in a few different scenarios, related to the spintronic and photothermoelectric properties of graphene. We make use of linear-scaling numerical simulation techniques to study systems containing many millions of atoms, thus reaching the experimental scale.<br/><br/>Owing to its small spin-orbit coupling and high carrier mobility, graphene has proven to be a highly efficient transporter of spin, with measured spin diffusion lengths in the tens or hundreds of microns. It is predicted that phonon scattering or local strain variations will serve as the ultimate limiting factor in spin transport. Here we present our use of numerical simulations to explore the upper limit of spin transport in graphene arising from thermally- and substrate-induced corrugations and strain variations.<br/><br/>Graphene is also extremely promising for its use as a high-speed, low-power photodetector in next-generation optical communications technologies. The performance of such photodetectors is ultimately limited by the interaction between hot electrons and dynamic strain variations, i.e., phonons. Defect-mediated electron-phonon interactions can also play a crucial role in the photodetector performance. Here we employ a time-dependent version of our numerical simulation tool to study the relaxation of hot carriers in graphene, mediated by the presence of both phonons and defects, and we explore avenues for optimizing the resulting photodetector performance.<br/><br/>Finally, we discuss a positive aspect of local strain variations in graphene – the electrical generation of pure spin currents via the spin Hall effect. By combining tailored local strain with spin-orbit coupling, we aim to significantly enhance the spin Hall effect in graphene. Here we will present our numerical simulations of this effect, and discuss its potential applicability for future low-power memories based on spin-orbit torque.