Abstract
The properties of the Kondo insulator in a strong magnetic field are one of the most intriguing subjects in condensed matter physics. The Kondo insulating state is expected to be suppressed by magnetic fields, which results in the dramatic change in the electronic state. We have studied the magnetization process of one of the prototypical Kondo insulators YbB 12 at several temperatures in magnetic fields of up to 80 T. The metamagnetism due to the insulator-metal (IM) transition seen around 50 T was found to become significantly broadened at approximately 30 K. This characteristic temperature T * ≈ 30 K in YbB 12 is an order of magnitude lower than the Kondo temperature T K = 240 K. Our results suggest that there is an energy scale smaller than the Kondo temperature that is important to understanding the nature of Kondo insulators.
Highlights
The Kondo insulator is a class of matter in which the Kondo effect is significant and the electrons are treated as quasiparticles termed heavy fermions [1]
The most striking feature of the Kondo insulator is that the energy gap opens at a low temperature and it becomes an insulator, in contrast to the fact that most of the materials experiencing the Kondo effect strongly are metal
The localized model can explain the properties of the Kondo insulators with diluted f electron systems, such as La1− x Ybx B12, the c- f hybridization gap model reproduces the behavior of magnetic properties of the Kondo insulators well [6]
Summary
The Kondo insulator is a class of matter in which the Kondo effect is significant and the electrons are treated as quasiparticles termed heavy fermions [1]. The most striking feature of the Kondo insulator is that the energy gap opens at a low temperature and it becomes an insulator, in contrast to the fact that most of the materials experiencing the Kondo effect strongly are metal (so-called heavy fermion system). One of the fundamental properties to be studied is the temperature dependence of the energy gap This is because the Kondo effect becomes significant only at low temperatures and the temperature variation should give crucial information regarding the mechanism of the gap formation. In addition to the interest in the mechanism of the energy gap’s formation, YbB12 has been collecting much attention because quantum oscillations have recently been observed in the insulating phase [7] and the origin is highly controversial; it could be due to the topological surface metallic state or bulk exotic quasi particles. Understanding of the electronic states in YbB12 has become one of the most intriguing issues to be urgently resolved
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