Material Development of Kondo Insulator Yb_1−xCa_xB₁₂ by High-Pressure Synthesis

Abstract

It has been recently found that Kondo insulator YbB 12 has the metallic state on the surface by transport properties and photoemission spectra etc. To study such exotic state in detail, we have investigated transport and magnetic properties of Yb 1-x R 3+ x B 12 (R 3+ = non-magnetic trivalent ions). Furthermore, we have succeeded in substitution of Ca 2+ for Yb site in YbB 12 by high-pressure synthesis. As Ca 2+ contents increase, the density of states at Fermi energy D(ε F) is expected to decrease gradually. The activation energies have been found to be almost constant in the range of 0 < x < 0.2. This result suggests that coherence of Kondo clouds in Ca-substituted alloys is maintained up to x = 0.2.