Mixed-valence insulators with neutral Fermi surfaces

Abstract

Samarium hexaboride is a classic three-dimensional mixed valence system with a high-temperature metallic phase that evolves into a paramagnetic charge insulator below 40 kelvin. A number of recent experiments have suggested the possibility that the low-temperature insulating bulk hosts electrically neutral gapless fermionic excitations. Here we show that a possible ground state of strongly correlated mixed valence insulators - composite exciton Fermi liquid - hosts a three dimensional Fermi surface of a neutral fermion, that we name the "composite exciton". We describe the mechanism responsible for the formation of such excitons, discuss the phenomenology of the composite exciton Fermi liquids and make comparison to experiments in SmB${}_6$.

arXiv commentFinal published version

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• Quantum oscillations in flux-grown SmB6 with embedded aluminum
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• Unconventional thermal metallic state of charge-neutral fermions in an insulator
• Unusual high-field metal in a Kondo insulator
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• Theory of competing excitonic orders in insulating WTe${}_2$ monolayers
• A highly asymmetric nodal semimetal in bulk SmB6
• Theory of Correlated Insulators and Superconductor at $\nu =1$ in Twisted WSe${}_2$
• Quantum oscillations in 2D insulators induced by graphite gates
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• Quantum Oscillations in the Magnetisation and Density of States of Insulators
• Critical role of magnetic moments in heavy-fermion materials: revisiting mysteries of SmB${}_6$
• Ultraviolet-Infrared Mixing in Marginal Fermi Liquids
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