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

我们成功地展示了近道半导体YbB_12在160 GPa下的半导体到金属的急剧转变和195 GPa时超导性的出现，该半导体具有较小的能隙（E_g/k_B ~ 200 K）。超导转变温度约为0.8 K，临界场约为800 Oe。在超高压环境下，这种转变可以通过使用专门的金刚石砧细胞（DAC）技术来观察。在YbB_12高达120 T的磁化响应中，在B = 50 T时，磁化强度急剧上升，并继续线性增加。这种磁化强度在B = 120 t附近似乎不饱和，需要施加B = 200 ~ 300 t的外场才能达到磁饱和。对于TmB_4，虽然在第七相中发现了具有斐波那契数列特征的磁性准晶格，但在P = 3 GPa时，该磁相变得更加稳定。

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.