PerspectiveSolid-State Physics

Quantum oscillations in an insulator

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Science  05 Oct 2018:
Vol. 362, Issue 6410, pp. 32-33
DOI: 10.1126/science.aau3840

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A major triumph of the quantum theory of solids was the explanation (Bloch-Wilson theory) of the vast difference in electrical resistivity (14 orders of magnitude) between insulators and metals. In a metal, the conduction electrons define a Fermi surface, whose existence leads to quantum oscillations in resistivity versus a magnetic field. Insulators, with bands completely filled, have no Fermi surface, so quantum oscillations should be absent. Recently, this deeply rooted distinction has been challenged by experiments (1). However, the interpretations were muddled by the existence of metallic states on the surface (2) and other factors. On page 65 of this issue, Xiang et al. (3) report torque and magnetoresistance experiments on the “Kondo insulator” YbB12, which becomes a bulk insulator below 10 K. They present a persuasive case for a bulk origin for the quantum oscillations detected in the resistance.