Ole Rømer Colloquium Tuesday 10 October 12.30 in 1525-626 Speaker: Yong P. Chen, Purdue University Title: Topological and two-dimensional materials: new playground for physics and devices Abstract: Topological materials and two-dimensional (2D) materials (including graphene) have become among the most actively studied systems in condensed matter physics emerged in the last decade, as also reflected in two recent physics Nobel prizes (2016 and 2010). These classes of materials, with significant overlap and connection between them, have also received attention beyond condensed matter physics, ranging from high-energy physics to electronics industries. These materials bring unprecedented freedom to realize and engineer novel electronic bandstructures (kinetic energy-momentum dispersion, used to be thought as a well-settled subject), create condensed matter analogs of Dirac/Weyl/Majorana fermions and other exotic particles, and are also considered promising in potential device applications for new ways of energy-efficient information processing, such as spintronics or perhaps even quantum computing. In this talk, I will discuss some of their unusual properties, potential applications and future prospects, drawing examples from a personal journey of experimental exploration of these materials. I will describe, for example, how they can defy our usual intuition about conductors, allowing a conductor cut in half to maintain the same conductance (as in a "topological insulator"), and two pieces of conductors (such as graphene) stacked together to behave like an insulator. Conduction by spin-helical Dirac fermions on the surface of topological insulators, can give rise to characteristic topological transport with "half-integer" quantum number measured in quantum Hall effect and Aharonov-Bohm effect, and may provide efficient ways to generate and store spin based information. Furthermore, these materials can serve as building blocks or inspirations to create more complex material structures and new states of matter so far difficult to realize. Coffee and cake will be available from 12.20