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Inspired by the long carrier lifetimes (electron-electron and electron-phonon) in graphene and other 2D materials we have designed and developed computational strategies to integrate designer 2D metals, starting with Argentene and Cuphene. Cuphene and Argentene are new 2D materials that consist of a single atomic layer of silver/copper. These 2D metals have the potential to exhibit 10 times the conductance of optimally-doped graphene, and 50 times that of conventional 3D copper lines scaled to 1 nm dimensions. Achieving high carrier density and mobility in a 2D material like Cuphene or Argentene, will be transformative for atomic-scale photonics (extremely relevant in next generation architectures) and optical elements such as monolayer waveguides, sensors, and emission control layers. Realizing the potential of 2D metals, truly monolayer metals, requires an understanding of single-crystalline atomic layers of metals. Further, we identify suitable combinations of substrates and metals, with computational screening of thermodynamic stability. In addition to 3D crystalline substrates, we also investigate the feasibility of metal monolayers on existing 2D materials in order to facilitate their incorporation into van der Waals stacks. This is an example of carrier lifetime-driven approach to quantum materials where we expect time-domain properties of a monolayer to be distinct from few-layer and bulk.
Taking this work further, we will discuss lifetimes and scattering in new classes of quantum materials including Weyl semimetals (WSMs). The field of topological materials with strong electron-electron interactions is well established and has been the subject of intense research over the past few decades. In parallel, the field of photonics has made tremendous progress in connecting spatio-temporal measurements of new quantum materials, including 2D plasmonics and Moir\'{e} structure localized potentials, to theoretical predictions. The study of the interplay between topological properties, quantum optics and plasmonic interactions in these materials has only very recently started to receive attention.
Experimental demonstrations in Type II Dirac/Weyl semimetals, materials where electrons effectively interact as massless relativistic particles (Weyl fermions) and in 3D the conduction and valence bands touch at isolated points, have shown evidence of a viscous electronic transport regime similar to hydrodynamic electron flow observed at charge neutrality in graphene. In this regime, electron-electron scattering dominates over impurity scattering and other momentum-relaxing processes so that momentum is quasi-conserved and electron flow can be described using the formalism of hydrodynamics. This leads to a variety of surprising behaviors such as breakdown of the Wiedemann-Franz law, appearance of electron vortices, and tunable viscosity via magnetic field in a Weyl semimetal. Understanding these physical processes in materials is of both fundamental and practical importance, yet these problems pose unique theoretical and computational challenges. The simultaneous contribution of processes that occur on many time and length scales, not only make direct computational approaches very difficult, they also make comparisons with experimental observations challenging. Here we report a new microscopic model of this behavior using a combination of ab initio scattering methods and fluid dynamics techniques. Our work establishes a connection between the observed hydrodynamic phenomena in Weyl semi metals, crystal structure and symmetry and their optical properties.
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