Collective modes identify elusive quantum material at room temperature
A new Cambridge experiment sheds light on an exotic state of matter that has defied discovery for decades.
The "excitonic insulator" is a quantum phase of matter which hosts collective state of electron-hole pairs known as excitons. Though first hypothesized in the 1960s, this state of matter has long evaded experimental detection. In the new experiment, the researchers study a proposed candidate material by exciting it with an intense laser pulse which generates "ripples" that move across the sample. The researchers found that these ripples propagate at great velocities and presist for distances much longer than should be possible if the ripples were carried by regular electrons, especially at room temperature. They propose instead that the ripples are carried by ordered collective motion of the electron-hole pairs of an excitonic insulator.
Remez and Cooper analyzed how such collective oscillations would be much more robust against common dissipation mechanisms compared to single electrons. They explain this with two compounding effects: that the electron-hole pairs are neutral, and that they can shift to protect each other from being scattered. They relate this robustness mathematically to the same framework that explains why the sky is blue. Their full treatment is published in Remez and Cooper, Phys. Rev. B 101 235129 (2020).
The nearly-dissipationless collective current observed in this experiment could one day underpin efficient low-power devices, as an alternative to long-sought-after room temperature superconductors.Imaging the coherent propagation of collective modes in the excitonic insulator Ta2NiSe5 at room temperature Science Advances 7 eabd6147 (2021)
Adapted from a Cavendish press release.