Speaker: Stephan Roche
Affiliation: Catalan Institute of Nanoscience Nanotechnology, Campus UAB, Bellaterra, Spain ICREA, Institució Catalana de Recerca i Estudis Avancats, Spain
Host: Professor Feng Yuan Ping
Location: Click HERE for directions
Abstract Details: The physics of graphene can be strongly enriched and manipulated by harvesting the large amount of possibilities of proximity effects with magnetic insulators, strong spin-orbit coupling SOC materials (transition metal dichalcogenides (TMD), topological insulators (TI), etc.). Simultaneously, the presence of extra degrees of freedom (sublattice pseudospin, valley isospin) points towards new directions for information processing [1,2], extending the playground to valleytronics, multifunctional electronic devices or novel quantum computing paradigms harnessing all these degrees of freedom in combination with electromagnetic fields or other external fields (strain, chemical functionalization) [2,3].
Here I will present some foundations of spin transport for Dirac fermions propagating in supported graphene devices or interfaced with strong SOC materials, with a particular emphasis on how spin dynamics is monitored by the nature of SOC induced in graphene by nearby TMDs and TIs. We will show that spin transport in these systems is distinguished by giant spin lifetime anisotropy, with spins oriented in the graphene plane relaxing much faster than spins pointing out of the plane [3-5]. This anisotropy arises from the specific nature of the SOC induced in the graphene layer, which depends crucially on the symmetry of the graphene/TMD & TI interfaces. In addition to serving as a probe of SOC induced in graphene, giant spin lifetime anisotropy may also prove useful for spintronics, for example serving as an orientation-dependent spin filter, or for enhancing spin Hall effect or spin-orbit torque efficiencies, in the perspective of spin torque technologies . The presence of weak antilocalization effects and the confirmation of a giant Spin Hall effect in such heterostructures will be also reported [7,8].
Finally I will question the recent interpretation of giant non-local resistance in terms of bulk valley Hall currents in graphene/hBN heterostructures . Our analysis suggests that the understanding of non-local transport properties requires advanced and realistic quantum transport calculations to account for subtle effects of edge physics in multiterminal transport measurements .
 S. Roche et al. 2D Materials 2, 030202 (2015). D.V. Tuan et al. Nature Physics 10, 857 (2014)
 D.V. Tuan & S. Roche, Phys. Rev. Lett. 116, 106601 (2016)
 A. Cummings, J.H. García, J. Fabian, S. Roche, Phys. Rev. Lett. 119, 206601 (2016)
 K. Song, D. Soriano, AW. Cummings, R. Robles, P. Ordejón, S. Roche, Nano Lett. 18, 2033(2018)
 D. Khokhriakov, A. Cummings, M. Vila, B. Karpiak, A. Dankert, S. Roche & S. Dash,
Science Advances 4 (9), eaat9349 (2018)
 J.H. García et al. Chem. Soc. Rev. 47, 3359-3379 (2018)
 J.H. García, A. Cummings, S. Roche, Nano Lett. 17, 5078 (2017)
 C.K. Safeer et al. Nano Lett. (arXiv:1810.12481, in press 2019)
 R. Gorbachev et al. Science 346 448 (2014)
 J. M. Marmolejo-Tejada et al. J. Phys. Materials. 1 (1), 015006 (2018);
A. Cresti et al. Rivista del Nuovo Cimento 39, 587 (2018)
About the Speaker: Prof. Stephan Roche is a theoretician with more than 25 years' experience in the study of Condensed Matter physics and particularly the transport theory of low-dimensional systems, including graphene and two-dimensional materials, carbon nanotubes, semiconducting nanowires, organic materials, quasicrystals, DNA and topological insulators. After serving as assistant Professor at the Université Joseph Fourier-UJF, and as a staff researcher of the Commissariat à l´Energie Atomique (Grenoble, France), he became ICREA Research Professor in 2010 and since then he is leading the “Theoretical and Computational Nanoscience” group at the Catalan Institute of Nanoscience and nanotechnology (ICN2), a flagship institute of the member of the Barcelona Institute of Science and Technology (BIST). He studied theoretical physics at Ecole Normale Supérieure (Lyon-France) and got his PhD at UJF. He has worked in France, Japan, Germany and Spain.
He has published about 200 papers in scientific journals and is the co-author of “Introduction to Graphene-Based Nanomaterials: From Electronic Structure to Quantum Transport” (Cambridge University Press, 2014) as well as the co-Editor of “Topological Insulators, Fundamentals and Perspectives” (WILEY 2015), and “Understanding carbon nanotubes: from Basics to Applications” (Lectures Notes Phys. Springer 2006). He has served as member of the Editorial Boards of 2D Materials (IoP) and the Rivista Nuovo Cimento (Italian Physical Society) for the past 4 years, and he is Chief Editor of Journal of Physics Materials (IoP) since early 2018. In 2009 he was awarded the Friedrich Wilhelm Bessel Research Award by the Alexander Von-Humboldt Foundation (Germany) in recognition of his outstanding contributions to the field of Computational Nanosciences. Since 2011 he has been actively involved in the European Graphene Flagship project, and currently appointed as the deputy leader of the spintronic work package.