Frequency Extension to THz Range in High Pressure ESR System and Its Application to Shastry-Sutherland Model Compound SrCu$_{2}$(BO$_{3}$)$_{2}$

摘要: We have made a survey of ceramics for the inner parts transmission-type pressure cell to achieve high and transmission in THz range. By using optimal combination ZrO$_{2}$-based ceramic Al$_{2}$O$_{3}$ ceramic, we succeeded obtaining up 1.5 GPa frequency region 700 GHz simultaneously. show high-pressure ESR results Shastry-Sutherland compound SrCu$_{2}$(BO$_{3}$)$_{2}$ as an application. observed direct transition modes between singlet ground state triplet excited states 1.51 successfully, obtained precise dependence gap energy. The energy is directly proved be suppressed by pressure. Moreover, found that system approaches quantum critical point with comparing data theory. This result also shows usefulness measurement study spin systems.