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Title: How can an insulator without a Fermi surface show quantum oscillations?
Plain: 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: 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.
Settled by: 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.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: (empty)
Posed since: 2015