Abstract: After the discovery of graphene and its so many fascinating properties, there has been a growing interest for the study of “artificial graphenes”. These are totally different and novel systems which bear exciting similarities with graphene. Among them are lattices of ultracold atoms, microwave or photonic lattices, “molecular graphene” or new compounds like phosphorene. The advantage of these artificial structures is that they serve as new playgrounds for measuring and testing physical phenomena which may not be reachable in graphene, in particular: the possibility of controlling the existence of Dirac points (or Dirac cones) existing in the electronic spectrum of graphene, of performing interference experiments in reciprocal space, of probing geometrical properties of the wave functions, of manipulating edge states, etc. These cones, which describe the band structure in the vicinity of the two connected energy bands, are characterized by a topological “charge”. They can be moved in reciprocal space by appropriate modification of external parameters (pressure, twist, sliding, stress, etc.). They can be manipulated, created or suppressed under the condition that the total topological charge be conserved. The merging between two Dirac cones is thus a topological transition that may be described by two distinct universality classes, according to whether the two cones have opposite or like topological charges. We have recently found a system in which the two classes may be observed.

 

In this presentation, I will discuss several aspects of the scenarios of merging or emergence of Dirac points as well as the experimental investigations of these scenarios in condensed matter and beyond.

 

Bio: Gilles Montambaux is director of research at the French CNRS (National Center for Scientific Research) since 1981. He spent one year as a postdoc at AT&T Bell laboratories and he conducts his research at the LPS (Laboratory of Solid State Physics) in Orsay, France where he has been head of the theory group for 9 years. He is also full professor at Ecole Polytechnique, France and he delivered lectures in a dozen of international schools. His research has been conducted in various directions of theoretical condensed matter physics including electronic properties of mesoscopic systems, disorder, interactions and phase coherence in condensed matter, physics in low dimension, hybrid systems normal/superconductor, graphene, physics of Dirac points. He is the founder and the first director of the French research network on Mesoscopic Physics. Since the discovery of graphene, he has been involved in the search for new physical systems outside the domain of condensed matter ranging from microwave systems to cold atoms physics, constituting the new domain of “artificial graphenes”. He received the Abragam prize (1992) and the Servant “grand prix” (2017) from the French Academy of Sciences. In addition to 200 research publications, he is the author of a monograph on “Mesoscopic Physics of Electrons and Photons”.