Speaker-Stephan Roche

Stephan Roche
ICREA/ICN2, Spain
Stephan Roche is ICREA Research Professor, head of the Theoretical and Computational Nanoscience Group of Catalan Institute of Nanoscience and Nanotechnology (ICN2). He is a theoretical physicist expert in quantum transport and in the development of computational modelling of nanomaterials and devices. His expertise includes the development of order N quantum transport (Kubo and Landauer-Büttiker conductances), with which he has pioneered mesoscopic transport studies in chemically disordered graphene-based materials and devices. He has a deep experience in developing advanced simulation tools in the context of industrial research, with collaborations including large companies such as NEC, ST Microelectronics, and SAMSUNG. He is co-supervising the GRAPHENE SPINTRONICS Work package within the Graphene Flagship project.
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Abstract

I will discuss charge, thermal and spin transport in chemically and structurally complex forms of graphene accounting from substrate effects, polycrystalline morphology of CVD graphene, and chemically functionalization; all aspects being of crucial relevance for the development of applications in flexible and transparent electronics, energy harvesting and spintronics. Multiscale simulation and predictive modelling will be demonstrated to enable calculations of physical properties in realistic models very large system sizes (with up to 1 billion atoms), reaching the experimental and technology scales.

First, one will focus on a quantitative analysis of transport properties in presence of structural imperfections as produced during the wafer-scale production of graphene through chemical growth (CVD), the chemical transfer to versatile substrates, and the device fabrication. Fundamental properties of charge mobilities in polycrystalline graphene, accounting the variability in average grain sizes and chemical reactivity of grain boundaries as observed in real samples grown by CVD will be presented, together with their relevance for device optimisation and diversification of applied functionalities such as chemical sensing [1]. In a second part, I will briefly mention our main results on spin transport in ultraclean sample in presence of electron-hole puddles and vanishingly small spin-orbit interaction (SOI) as well as in chemically disordered graphene with strongly enhanced SOI [2,3]. Unique spin dynamics phenomena in graphene, such as the formation of the Quantum Spin Hall state and a crossover to the Spin Hall effect under ad-atom segregation have been discovered [3], as well as the role of spin-pseudospin entanglement in driving the spin relaxation mechanism in the ultraclean graphene limit (graphene on BN substrate), or the manifestation of Dyakonov-Perel mechanism for graphene on SiO2 [2]. These results clarify current controversies and open unprecedented perspectives for achieving proofs of concepts of spin manipulation, contributing to the progress towards non-charge based revolutionary information processing and computing.

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Abstract: Minyang Lu

Sponsor: Wenyang Yang

Media: Xiaoyan Zhang

Visa: Xiaoqing Huang

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