Ruben Verresen (Harvard) - "Intrinsically gapless topological phase"

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Topology in quantum matter is typically associated with gapped phases. For example, in symmetry protected topological (SPT) phases, the bulk energy gap localizes edge modes near the boundary. In this talk, I introduce a new mechanism that leads to topological phases which are not only gapless but where the absence of a gap is essential. These `intrinsically gapless SPT phases' have no gapped counterpart and are hence also distinct from recently discovered examples of gapless SPT phases. The essential ingredient of these phases is that on-site symmetries act in an anomalous fashion at low energies. Intrinsically gapless SPT phases are found to display several unique properties including (i) protected edge modes that are impossible to realize in a gapped system with the same symmetries, (ii) string order parameters that are likewise forbidden in gapped phases, and (iii) constraints on the phase diagram obtained upon perturbing the phase. The predictions of the general theory are verified in a specific realization protected by Z_4 symmetry, the one dimensional Ising-Hubbard chain, using both numerical simulations and effective field theory. Time permitting, I will discuss extensions to higher dimensions and possible experimental realizations.

Видео Ruben Verresen (Harvard) - "Intrinsically gapless topological phase" канала harvard_mit_cmt_seminar