Charge-Neutral Electronic Excitations in Quantum Insulators

Abstract

Experiments on quantum materials have uncovered many interesting quantum phases ranging from superconductivity to a variety of topological quantum matter including the recently observed fractional quantum anomalous Hall insulators. The findings have come in parallel with the development of approaches to probe the rich excitations inherent in such systems. In contrast to observing electrically charged excitations, the detection of charge-neutral electronic excitations in condensed matter remains difficult, though they are essential to understanding a large class of strongly correlated phases. Low-energy neutral excitations are especially important in characterizing unconventional phases featuring electron fractionalization, such as quantum spin liquids, spin ices, and insulators with neutral Fermi surfaces. In this perspective, we discuss searches for neutral fermionic, bosonic, or anyonic excitations in unconventional insulators, highlighting theoretical and experimental progress in probing excitonic insulators, new quantum spin liquid candidates and emergent correlated insulators based on two-dimensional layered crystals and moiré materials. We outline the promises and challenges in probing and utilizing quantum insulators, and discuss exciting new opportunities for future advancements offered by ideas rooted in next-generation quantum materials, devices, and experimental schemes.

23 pages, 4 figures; A Perspective/Review Article published in Nature

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Cited by in corpus (7)

• First-principles design of excitonic insulators: A review
• Spin-Triplet Excitonic Insulator in the Ultra-Quantum Limit of HfTe5
• Identifying topological excitonic insulators via bulk-edge correspondence
• Gate tuning of coupled electronic and structural phase transition in atomically thin Ta${}_2$NiSe${}_5$
• Topological spin-up triplet excitonic condensation in two-dimensional electron-hole systems
• Propagating Collective Spin-valley Modes in Twisted WSe2
• Stabilization of sliding ferroelectricity through exciton condensation