Fermi surfaces in Kondo insulators

Abstract

We report magnetic quantum oscillations measured using torque magnetisation in the Kondo insulator YbB₁₂ and discuss the potential origin of the underlying Fermi surface. Observed quantum oscillations as well as complementary quantities such as a finite linear specific heat capacity in YbB₁₂ exhibit similarities with the Kondo insulator SmB₆, yet also crucial differences. Small heavy Fermi sections are observed in YbB₁₂ with similarities to the neighbouring heavy fermion semimetallic Fermi surface, in contrast to large light Fermi surface sections in SmB₆ which are more similar to the conduction electron Fermi surface. A rich spectrum of theoretical models is suggested to explain the origin across different Kondo insulating families of a bulk Fermi surface potentially from novel itinerant quasiparticles that couple to magnetic fields, yet do not couple to weak DC electric fields.