MATHEMATICAL SCIENCES

For the first time, scientists revealed exciton topological order


The collaborative team composed of Nanjing University, Peking University, and the University of Massachusetts Elmhurst has made important progress in the study of exciton topology in electron-hole correlation systems. This work theoretically proposes a new mechanism for associating the boson topological order generated by strong quantum fluctuations caused by the blocking effect of excitons. A novel topological state of time inversion symmetry breaking formed by excitons was observed experimentally in the InAs/GaSb quantum well with unbalanced electron-hole concentration, and the exciton topology order was revealed for the first time by combining experiment and theory. The findings were published online in Nature on June 14.

(left) Moat bands formed in double-layer quantum wells with unbalanced electron-hole density; (Right) Complete phase diagram of the two-layer quantum well exciton system Courtesy of the research group

The fractional quantum Hall effect is one of the frontier research hotspots in contemporary condensed matter physics, and the related research won the 1998 Nobel Prize in Physics. The fractional quantum Hall effect originates from the correlation effect of electrons, which leads to the generation of topological order, showing long-range quantum entanglement, evolutionary gauge field and fractional excitation, which has potential application value in future topological quantum computing. A natural question is: Is it possible to produce fractional quantum Hall states with topological order in interacting boson systems? Studies in cold atomic systems were first attempted, but remained exploratory for many years.

This work studies the electron-hole coupled bilayer system and finds that when the electron and hole concentrations are unbalanced, the excitons produced by the system have MOAT-type bands (the dispersion of the excitons presents a circle of highly degenerate in the momentum space). The blocking effect of the exciton moat band makes the exciton do not undergo boson condensation, which in turn produces a class of topological orders with long-range quantum entanglement, the physical image of which is equivalent to the fractional quantum Hall state formed by excitons. Compared with the results of traditional mean field theory, this work finds that quantum fluctuations lead to the emergence of a new exciton topological sequence region in the traditional exciton condensation phase diagram.

The exciton topology is generated in the interval of unbalanced electron and hole concentration, opens the bulk energy gap, and has a chiral edge state formed by a pair of electron-hole formations. At zero magnetic field, electrons and holes carry opposite charges, resulting in helical-like edge transport. Unlike the quantum spin Hall effect, the exciton topology does not require the protection of time inversion symmetry, and this pair of edge states does not open the energy gap under the vertical magnetic field, but separates in real space, resulting in the transition of the edge state transport signal from helix-like to chiral-like. The mutual confirmation of the above theory and experiment reveals the exciton topology due to the blocking and correlation effects in the electron-hole bilayer system. (Source: Wen Caifei, China Science News)

Related paper information:https://doi.org/10.1038/s41586-023-06065-w



Source link

Related Articles

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button