Detta är en digital seminarieserie i kondenserade materiens fysik och atomfysik, med syfte att koppla samman forskare från olika nordiska universitet. Samtalen är informella och ska inspirera till diskussioner och interaktioner.
One standard assumption for classifying topological phases of matter is that the system has an (at least partial) energy gap. More precisely, the corresponding topological invariants become generically ill-defined when the system becomes gapless, i.e. at critical points. Nevertheless, it was observed that certain hallmarks of topological phases, in particular the presence of robust edge modes, survive at criticality. In this talk, we discuss two distinct ways of how to generalize topological invariants to systems without an energy gap, as well as their properties. We will also introduce a relation between critical hermitian and gapped non-hermitian phases, using the example of one-dimensional systems with chiral symmetry.
Zoom-länk: https://nordita.org/zoom/nvcms