Phys.org August 27, 2024
Due to their bosonic nature, excitons are expected to condense and exhibit superfluidity at sufficiently low temperatures. In interacting Chern insulators, excitons may inherit the nontrivial topology and quantum geometry from the underlying electron wavefunctions. A team of researchers in the US (University of Oklahoma, City University of New York, Harvard University) theoretically investigated the excitonic bound states and superfluidity in flat-band insulators pumped with light. They found that the exciton wavefunctions exhibited vortex structures in momentum space, with the total vorticity being equal to the difference of Chern numbers between the conduction and valence bands. The exciton binding energy and the exciton superfluid density were proportional to the Brillouin-zone average of the quantum metric and the Coulomb potential energy per unit cell. They proposed that the vorticity could be experimentally measured via the nonlinear anomalous Hall effect, whereas the exciton superfluidity could be detected by voltage-drop quantization through a combination of quantum geometry and Aharonov–Casher effect. Topological excitons and their superfluid phase could be realized in flat bands of twisted Van der Waals heterostructures… read more. TECHNICAL ARTICLEÂ
Artist rendering of an exciton (e) and its hole (h) circling one another. Credit: Daniel Deering, University of Oklahoma