凯发

I will present a successful computational strategy to investigate quantum (charge, phonon and spin) transport in structurally or/and chemically complex materials such as graphene, topological insulators, or organic matter, for which it is necessary to go beyond phenomenological approaches. The possibility to combine first principles calculations with tight-binding models, together with the development of order N algorithms which are free from any matrix inversion/diagonalization give access to the study of quantum transport phenomena in realistic models of complex materials containing up to 1 Billion atoms. Such methodologies allow direct comparison with experiments, and can hence serve as guiding tools for technology optimization, as well as new tools for discovering quantum phenomena out of reach from conventional perturbative treatments and semi-classical transport approaches.

One illustration will be the quantitative analysis on the transport properties of the damage produced during the wafer-scale production of graphene through chemical growth (CVD), or the mechanical/chemical exfoliation and chemical transfer to versatile substrates, followed by the device fabrication. Fundamental properties of charge transport in polycrystalline graphene, accounting the variability in average grain sizes and grain boundaries imperfections as observed in real samples grown by CVD will be presented, together with their relevance for device optimization and diversification of technological functionalities. Other illustrations will include thermal transport in hybrid boron nitride (BN)/graphene materials, or BN/graphene heterostructures which display fascinating physics such as the Hofstadter butterfly.

A second type of applications will focused on the study spin-orbit interaction induced by dilute ad-atom (gold, thallium) deposits on graphene.  Unique phenomenon of the spin-dynamics in graphene (such as Spin Quantum Hall effect), as well as quantitative evaluation of spin precession times and spin-relaxation times as a function of charge density will be reported. Such findings will be shown to open novel perspectives for spin manipulation, contributing to the future advent of non-charge based revolutionary information processing and computing.

Reference:

[1] L. E. F. Foa Torres, S. Roche, and J. C. Charlier, Introduction to Graphene-Based Nanomaterials: From Electronic Structure to Quantum Transport (Cambridge University Press, Cambridge, 2014). 

[2] S. Roche, N. Leconte, F. Ortmann, A. Lherbier, D. Soriano, and J.-C. Charlier, Solid State Communications 152, 1404 (2012).

[3] D. Van Tuan, J. Kotakoski, T. Louvet, F. Ortmann, J. C. Meyer, and S. Roche, Nano Lett. 13, 1730−1735 (2013)

[4] A.W. Cummings, D. Loc Duong, V. Luan Nguyen, D. Van Tuan, J. Kotakoski , J.E. Barrios Vargas, Y. Hee Lee, S. Roche; Advanced Materials 2014 DOI: 10.1002/adma.20140138