Research for novel ordered phase under the high pressure on strongly correlated rare-earth borides

在低能隙(E_g/k_B~200K)的近藤半导体YBB_(12)中，我们成功地展示了160 GPa时半导体到金属的戏剧性转变和195 GPa时超导电性的出现。超导转变温度约为0.8K，其临界场为800Oe。这种超高压环境下的转变可以用一种特殊的金刚石顶压室(DAC)技术来观察。YBB_(12)在120T以下的磁化响应中，在B=50T时，磁化强度急剧上升，并继续线性增加。当外加磁场B=200-300T时，这种磁化强度似乎并不饱和。至于TMB_4，虽然在第VII相中发现了以斐波那契序列为特征的磁准晶格，但发现这种磁相在P=3 GPa时变得更稳定。

We have succeeded in exhibition of dramatic semiconductor-to-metal transition at 160 GPa and appearance of superconductivity at 195 GPa in Kondo semiconductor YbB_12 which has a small energy gap (E_g/k_B ~ 200 K). Superconducting transition temperature is of about 0.8 K and its critical field is evaluated to be 800 Oe. This transition under ultra high-pressure environment can be observed by using a specialized diamond anvil cell (DAC) technique. In the magnetization response of YbB_12 up to 120 T, the magnetization steeply jumps up at B = 50 T, and continues to increase linearly. This magnetization dose not seem to saturate around B = 120 T. It would be necessary for magnetic saturation to apply the external field B = 200 - 300 T.As for TmB_4, although the magnetic quasi-crystal lattice characterized by a Fibonacci sequence was found in the phase VII, it is found out that this magnetic phase becomes more stable up to P = 3 GPa.