title: Frequency Extension to the THz Range in the High Pressure ESR System and Its Application to the Shastry-Sutherland Model Compound SrCu2(BO3)2.
abstract: 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.
authors.affiliation: Molecular Photoscience Research Center, Kobe University , Kobe 657-8501, Japan.|Graduate School of Science, Kobe University , Kobe 657-8501, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Ohta
authors.affiliation: Center for Supports to Research and Education Activities, Kobe University , Kobe 657-8501, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Sakurai
authors.affiliation: Graduate School of Science, Kobe University , Kobe 657-8501, Japan.
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Matsui
authors.affiliation: Graduate School of Science, Kobe University , Kobe 657-8501, Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Kawasaki
authors.affiliation: Graduate School of Science, Kobe University , Kobe 657-8501, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Hirao
authors.affiliation: Molecular Photoscience Research Center, Kobe University , Kobe 657-8501, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Okubo
authors.affiliation: Institute for Solid State Physics, University of Tokyo , Kashiwa 277-8581, Japan.
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Matsubayashi
authors.affiliation: Institute for Solid State Physics, University of Tokyo , Kashiwa 277-8581, Japan.
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Uwatoko
authors.affiliation: Department of Physics, Okayama University , Okayama 700-8530, Japan.
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Kudo
authors.affiliation: Department of Applied Physics, Tohoku University , Sendai 980-8579, Japan.
authors.forename: Yoji
authors.initials: Y
authors.lastname: Koike