Enhancement of Superconductivity of Beryllium at High Pressure

Among elements shows superconductivity at high pressure, some elements show the large enhancement of the transition temperature (Tc) at higher pressures. In the case of lithium, the Tc at ambient pressure is 0.4 mK which is the lowest observed value in whole elements, however, is enhanced by pressure up to near 20 K [1]. And calcium, which is on the same group II and not superconductive at ambient pressure, shows the highest Tc of elements at 29 K under pressure [2]. Then we focused on beryllium which is near to them on the periodic table. At ambient pressure, Tc of beryllium is 24 mK. We measured the electrical resistance at high pressure (P\textless 50 GPa) and low temperature (T\textgreater 100 mK) and found that the Tc rose up to few Kelvin at pressure above 20 GPa and reached up to 3.7 K at 30 GPa. In this pressure range the hcp crystal structure is stable at room temperature. We performed a powder X-ray diffraction measurement at room temperature and low temperature in BL10XU at SPring-8 and found a discontinuous change in c/a ratio at around 25 GPa.\\[4pt] [1] K. Shimizu, H. Ishikawa, D. Takao, T. Yagi and K. Amaya, Nature 419, 597-599 (2002).\\[0pt] [2] M. Sakata, Y. Nakamoto, and K. Shimizu, Phys. Rev. B 83, 220512 (2011).\\[0pt] [3] K. Nakano, Y. Akahama and H. Kawamura, J. Phys.: Condens. Matter 14, 10569--10573 (2002).