Non-magnetic element substitution effect in Kondo insulator YbB12 and exotic surface effect in this alloy system

Abstract

Kondo temperature TK’s for Kondo insulator alloys Yb1-xRxB12 (R = Y, Lu, Sc and Zr) show drastic variation as every x increase. It is found that YbB12 in a virtual gap-less state would have a peak at about 25 K in magnetic susceptibility χ(T) from analysis of χ(T) of all these alloys. Up-turns shown in χ(T) below 20 K grow as development of an energy gap ΔE. Those behaviors may be related to the second-gap development within the in-gap state showing metallic behaviors.

The Temperature Dependence of the Magnetization Process of the Kondo Insulator YbB12

“…Such a characteristic temperature lower than the Kondo temperature has been reported in a heavy fermion compound YbRh 2 Si 2 [22], and the spatial coherence of the Kondo effect is important in this case. On the other hand, a detailed study of element substitution effect of YbB 12 in Yb 1−x R x B 12 (R = Y, Lu, Sc) has also revealed that there can be another Kondo temperature of around 25 K in YbB 12 [23]. This temperature corresponds to the Kondo temperature in the hypothetical metallic YbB 12 and can be said to be a sort of hidden energy scale in the insulating phase of YbB 12 whose T K is 240 K. If we consider the IM transition as a transition from a local Kondo state to a Kondo metal state, it can be said that the local character is suppressed at T * , although the energy gap is still expected to be open.…”

Material Development of Kondo Insulator Yb1−xCaxB12 by High-Pressure Synthesis

“…We have estimated the magnitude of the energy gaps ΔE from the Arrhenius plots of all of the resistivity (Figure 3 shows temperature variation in log T scale.). In trivalent ion substitution case, ΔE decreases with increase of x [2]. On the other hands, in the divalent ion substitution case, as shown in Fig.…”

“…In summary, we have succeeded in High-pressure synthesis of Yb 1-x Ca x B 12 . Substitution rate dependence of Ca-alloy in electrical resistivity is different from trivalent and tetravalent substitution alloys cases [2]. In the Ca-alloys the evaluated energy gap is almost constant up to x = 0.2.…”