Does insulating YbB12 host a Fermi surface of neutral fermions?
In plain words
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 statement
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.
What would settle it
Thermal transport and heat-capacity oscillations on crystals of varied purity, showing the fermion contribution is bulk and independent of metallic inclusions.
Status in the literature
Unverified 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).
Related problems
- Special case of Do Kondo insulators host charge-neutral fermions with a Fermi surface · YbB12 is one of the Kondo insulators in the neutral-fermion question
- Special case of How can an insulator without a Fermi surface show quantum oscillations?