Electron spin resonance studies on the energy gap in YbB 12

Abstract

Using electron spin resonance (ESR) we have studied Kondo dielectric YbB 12. An energy gap with the width of 2Δ=12 meV is found in the electronic spectrum of YbB 12. We have treated our experimental data within the model of excitonic dielectric and determined the temperature dependence of the gap: Δ(T)=72 K at zero temperature and Δ( T)=0 at about 115 K. The singularity in temperature dependence of the ESR linewidth observed at 13–15 K indicates the existence of finite density of electronic states inside the gap which can be caused by impurity states or bound polaron excitations of the electron spectrum.