R. Banerjee, V-H Nguyen, T. Granzier-Nakajima, L. Pabbi, A. Lherbier, J.-C. Charlier, M. Terrones, E. Hudson
Pennsylvania State University,
Keywords: graphene, straintronics, extreme strain, ripples, suspended graphene, STM, pseudo-magnetic fields
Summary:The response two-dimensional materials to strain can vary dramatically from that of bulk materials. For example, whereas traditional materials like silicon typically break for strains near 1.5%, graphene can withstand extreme strains of over 20%. The impact of strain can be particularly interesting when modulated at the nanoscale. In this talk, I will present a recipe to engineer extreme (>10%) strain in suspended graphene by draping it over large (up to 35nm) Cu step edges. Analogous to a draped tablecloth, nanoscale periodic ripples arise as the graphene is pinned and pulled by the contact forces of the substrate. Scanning tunneling microscopy (STM) of these ripples reveals that classical scaling laws fail to explain their shape. Instead, other conserved quantities emerge - the draping and rippling angles. Thus suspended graphene behaves like a bizarre fabric that regardless of how it is pulled always buckles at the same angle. Furthermore, Scanning Tunneling Spectroscopy (STS) measurements reveal Landau levels in the presence of highly non-uniform intense (~200T) pseudo-magnetic fields. DFT and tight binding calculations imply the existence of counterpropagating valley Hall states at the crests and troughs of the ripples, reminiscent of topological materials.