Editor’s Suggestion: Self-trapped polarons and topological defects in a topological Mott insulator

15 December 2020

How can the interplay between spontaneous symmetry breaking and global topological properties lead to  new, strongly correlated topological effects? Prof. Markus Müller (PGI-2/RWTH Aachen University) and Sergi Julià-Farré, Prof. Maciej Lewenstein and Dr. Alexandre Dauphin (Institute of Photonic Sciences (ICFO), Barcelona, Spain) report on the results of their theoretical research in this area in the renowned journal Physical Review Letters. The researchers also propose an experimental demonstration on systems of cold laser-excited Rydberg atoms. The article was selected by the editors as an “Editor’s Suggestion”.

Over the last decades, topological insulators have not only attracted great interest, but have also offered promising applications in areas such as metrology or quantum computation. These exotic materials go beyond the standard classification of phases of matter: they are insulating in their bulk, conducting at their edges, and characterized by a global topological invariant, in contrast to a local order parameter as in the conventional Ginzburg-Landau theory of phases of matter.

Such topological phases have been experimentally observed in condensed matter systems and more recently in quantum simulators. The latter are very versatile platforms that allow one to simulate a material with another quantum system in a very controllable environment. In the case of topological insulators, this degree of control is particularly promising to unveil the mechanisms leading to these phases.

The quantum simulation of these exotic materials typically relies on the generation of artificial gauge fields. However, recent studies have shown that topological phases can also emerge from particle interactions. The latter mechanism leads to the concept of interaction-induced topological phases, in which topology is acquired through a spontaneous symmetry breaking process. The interplay of the spontaneous symmetry breaking with the global topological properties can lead to very interesting effects.

In their article, Sergi Julià-Farré, Maciej Lewenstein, Alexandre Dauphin, and Markus Müller report how such interplay can lead to new, strongly-correlated topological effects. The team of researchers has shown how interactions can localize particles in the insulating bulk, leading to self-trapped polarons. Moreover, they have also shown how the interacting nature of the topological insulator gives rise to domains in the bulk. 

“Interestingly, the nontrivial topology associated with each domain leads to the appearance of protected conducting states in the bulk, localized at the domain boundaries”, says Markus Müller. The researchers also discussed the possibility of quantum simulating such phases with cold laser-excited Rydberg atoms in an optical lattice. 

More information:

Original publication:

Self-Trapped Polarons and Topological Defects in a Topological Mott Insulator;
Sergi Julià-Farré, Markus Müller, Maciej Lewenstein, and Alexandre Dauphin; Phys. Rev. Lett. 125, 240601 – Published 8 December 2020; DOI:

10.1103/PhysRevLett.125.240601