**Clément Dutreix (LOMA Bordeaux)**

Wavefront dislocations reveal the nontrivial bulk of topological systems

(Séminaire zoom: https://zoom.us/j/3630156422?pwd=anVyV3BkUXQ5RDVwaGg2SFk0NzlnZz09 ID de réunion : 363 015 6422 Code secret : HGPw34 )

In 1974, John Nye and Michael Berry discovered a fundamental wave phenomenon: The surfaces of constant phase may exhibit wavefront dislocations [1]. The dislocation source is a phase singularity in the wavefield and does involve any wave equation. Wavefront dislocations are then ubiquitous, from the physics of tides and sound to electromagnetism and singular optics. Singularities in the phase of wave functions are also at the heart of the characterisation of topological quantum matter. Despite identical singular features, topological phases and singular waves have remained two distinct fields. I will present two experiments that aim to image the fluctuations of the local density of states nearby boundaries in topological systems. The first experiment focuses on quasiparticle interference in graphene imaged by scanning tunneling microscopy [2]. The second experiment emulates a 1D insulator with dielectric resonators inside a microwave cavity [3]. Although these experimental systems are quite different — 2D electronic semimetal and 1D microwave insulator — both of them exhibit wavefront dislocations in their local density of states. I will show that the dislocation strength is a real-space measure of the nontrivial bulk topology, demonstrating a novel approach to identify topological systems in the experiments.

[1] J. F. Nye & M. V. Berry, Dislocations in wave trains. Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences 336, 165–190 (1974)

[2] C. Dutreix, H. González-Herrero, I. Brihuega, M. I. Katsnelson, C. Chapelier, and V. T. Renard, Measuring the Berry phase of graphene from wavefront dislocations in Friedel oscillations, Nature 574, 219–222 (2019)

[3] C. Dutreix, M. Bellec, P. Delplace, and F. Mortessagne, Wavefront dislocations reveal insulator topology, arXiv:2006.08556