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Frequency Extension to the THz Range in the High Pressure ESR System and Its Application to the Shastry–Sutherland Model Compound SrCu2(BO3)2 B

Ohta, Hitoshi, Sakurai, Takahiro, Matsui, Ryosuke, Kawasaki, Kohei, Hirao, Yuki, Okubo, Susumu, Matsubayashi, Kazuyuki, Uwatoko, Yoshiya, Kudo, Kazutaka, Koike, Yoji
The Journal of physical chemistry 2015 v.119 no.43 pp. 13755-13761
aluminum oxide, ceramics, energy, models, phase transition, surveys
We have made a survey of ceramics for the inner parts of the transmission-type pressure cell to achieve the high pressure and the high transmission in the THz range. By using the optimal combination of ZrO₂-based ceramic and Al₂O₃ ceramic, we have succeeded in obtaining a pressure up to 1.5 GPa and a frequency region up to 700 GHz simultaneously. We show the high-pressure ESR results of the Shastry–Sutherland compound SrCu₂(BO₃)₂ as an application. We observed the direct ESR transition modes between the singlet ground state and the triplet excited states up to a pressure of 1.51 GPa successfully, and obtained the precise pressure dependence of the gap energy. The gap energy is directly proved to be suppressed by the pressure. Moreover, we found that the system approaches the quantum critical point with pressure by comparing the obtained data with the theory. This result also shows the usefulness of high-pressure ESR measurement in the THz region to study quantum spin systems.