Research Highlights
A Dominant Role for Quantum Fluctuations
A recent theoretical study has made the surprising finding that certain physical properties of interacting insulators are dominated by quantum fluctuations, even when the non-fluctuating (mean-field) theory is sufficient to describe the phase diagram.
This work follows on the heels of two recent high profile experimental results. First is the realization of long-sought excitonic condensation and the resulting excitonic insulator state using layered 2D semiconductor systems, now allowing for active exploration of this state’s exotic properties. Second are the unexpected, and still not understood, measurements in Kondo insulators showing clear and sizable ``quantum oscillations" of the magnetization with magnetic field, which classic theory says should not be possible.
Through a careful theoretical analysis of the quantum oscillations in an interaction-driven excitonic insulator, we find that this effect cannot be understood with the standard semiclassical arguments within mean-field theory, even when the mean-field theory is well controlled and sufficient to establish the phase diagram. Instead, we show that quantum fluctuations of the Higgs and phase modes of the excitonic order are responsible for generating the dominant contribution to quantum oscillations, completely unlike other settings. For parameter regimes like those in the 2D experiments noted above, we find that these fluctuation-generated quantum oscillations may even be orders of magnitude larger than what established theory predicts for a corresponding noninteracting and therefore (semi)metallic system, which one might have expected to set an upper limit on the size of the effect.
Andrew A. Allocca and Nigel R. Cooper Phys. Rev. Research 6, 033199 (2024),