Giulia Venditti won a SNSF postdoctoral fellowship

Giulia Venditti, in the group of Louk Rademaker, UNIGE, obtains a highly competitive SNSF postdoctoral fellowship. The main aim of the project Xtra-Ordinary Vortices (XVORTEX) is to study the intertwining of topological defects and the topology of the electronic degrees of freedom in novel 2D systems.

We are in fact witnessing a real “2D revolution” in the engineering and study of low dimensional materials. The 2D nature of such novel systems immediately calls for the Berezinskii-Kosterlitz-Thouless (BKT) theory, which allows to recover quasi-long-range order, otherwise prohibited by the Mermin-Wagner theorem. Its wide universality class also embraces 2D superconductors, and 2D magnets with easy-plane symmetry. 

The BKT transition is driven by the proliferation of topological defects, namely vortex-antivortex pairs, leading to the algebraic quasi-long-range order. However, non-trivial structures of the vortices are expected when the underlying symmetry breaking order parameters are themelves unconventional. This includes the fermionic and possibly topological nature of such order parameters. Indeed, in various 2D materials we find multiple (broken) symmetries, topological flat bands, an interplay among many order parameters, as well as possible Majorana zero modes. All of this might result in extra-ordinary properties and interactions among vortices, driving and changing the algebraic long-range order and the transition. In such situations, the BKT universality class might be compromised and/or vestigial phases could be revealed. 

The aim of the project is to provide a new theoretical framework for vortex-driven phases and phase transitions, and a particular effort will be dedicated to the search for experimentally accessible fingerprints (STM, transport measurements, …).