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Title: Does insulating YbB12 host a Fermi surface of neutral fermions?
Plain: YbB12 shows oscillations in resistance and magnetization, plus heat capacity and heat conduction that grow linearly with temperature as in a metal, while remaining electrically insulating.
Precise: In YbB12, quantum oscillations in resistivity and magnetization appear in the insulating state above $\sim 3.5e5\,\mathrm{G}$ (Xiang et al. 2018), heat-capacity oscillations with frequency $\sim 6.7e6\,\mathrm{G}$ were reported in 2025, and zero-field specific heat and thermal conductivity have linear-in-$T$ terms (Sato et al. 2019). Determine whether these signals come from a bulk Fermi surface of charge-neutral fermions.
Settled by: Thermal transport and heat-capacity oscillations on crystals of varied purity, showing the fermion contribution is bulk and independent of metallic inclusions.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: contested
Status note: Heat-capacity oscillations at a frequency matching torque and transport, with amplitude about 13 percent of the linear specific-heat coefficient, were reported in 2025 (Chen et al., Physical Review Letters 135, 156501, arXiv 2501.07471).
Posed since: 2018