High-temperature antiferromagnetism in Yb based heavy fermion systems proximate to a Kondo insulator

Suzuki, Shintaro*; Takubo, Ko*; Kuga, Kentaro*; Higemoto, Wataru  ; Ito, Takashi   ; Tomita, Takahiro*; Shimura, Yasumichi*; Matsumoto, Yosuke*; Bareille, C.*; Wadachi, Hiroki*; Shin, S.*; Nakatsuji, Satoru*

We report our experimental discovery of the transition temperature reaching 20 K in a Yb-based compound at ambient pressure. The Mn substitution at the Al site in an intermediate valence state of -YbAlB not only induces antiferromagnetic transition at a record high temperature of 20 K but also transforms the heavy-fermion liquid state in -YbAlB into a highly resistive metallic state proximate to a Kondo insulator.