How can an insulator without a Fermi surface show quantum oscillations?
In plain words
Quantum oscillations normally require a sharp boundary between filled and empty electron states, which an insulator lacks. Proposed explanations range from field effects on the insulating gap to new particles that carry no charge.
Precise statement
Candidates are Landau quantization of hybridized bands with a small inverted gap, which gives magnetization oscillations at the frequency of the unhybridized Fermi surface (Knolle and Cooper 2015); emergent neutral fermions with a Fermi surface (spinons, composite excitons, Majorana Fermi sea); and in-gap impurity bands or metallic inclusions. An answer predicts the frequency, the amplitude temperature dependence including deviations from Lifshitz-Kosevich form, and which quantities oscillate (magnetization, resistivity, heat capacity, thermopower) in SmB6, YbB12 and monolayer WTe2.
What would settle it
Amplitude versus temperature and gap size in a tunable system (pressure-tuned YbB12, gate-tuned WTe2 or InAs/GaSb wells) where the candidate theories make distinct predictions.
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