Okazaki Laboratory is a condensed matter physics research group in Tokyo University of Science founded in 2015. Our group studies exotic electronic properties emerged in the strongly correlated electron systems including oxides, organic salt and rare-earth compounds. We also focus on the electron transport behavior under illuminations or in high electric fields to examine non-equilibrium nature of correlated electrons.
Temperature gradient applied in a material generates the thermoelectric voltage, known as the Seebeck effect. We study anomalous Seebeck effect in transition-metal oxides due to an entangled spin and orbital degrees of freedom in correlated electrons.
Nonlinear conduction in correlated electron systems
Correlated insulators such as charge order and Mott insulators show characteristic non-Ohmic response in the high-field range. We explore such a non-equilibrium aspect of correlated carriers by utilizing transport and thermodynamic measurements under currents.
Infrared spectroscopy is a powerful probe to grasp the electronic structure in the broad energy range. We apply this technique to the correlated electron systems, and also utilize the spatially-resolved "imaging" measurements to study the inhomogeneous electronic state.
Current-induced lattice deformation in a ruthenium oxide
Ca2RuO4 exhibits unusual electric-field response. Through a combined transport and synchrotron radiation x-ray measurement, we find that an electrical current, a non-equilibrium quantity, causes the change in the lattice constants of this material.
Scaling in low-temperature transport coefficients of doped CuRhO2
We performed a systematic evolution of the resistivity and the Seebeck coefficient in hole-doped CuRhO2 single crystals, and found a relation in those transport coefficients, which can be applicable to the correlated materials with low carrier densities.
Enhancement of low-temperature Seebeck coefficient in KxRhO2
Layered cobaltite NaxCoO2 is a well-known thermoelectric oxide. We examine the transport properties of the isovalent KxRhO2, and find an unusual enhancement of the Seebeck coefficient at a critical K content.
H. Sakabayashi and R. Okazaki
"Crossover from itinerant to localized states in the thermoelectric oxide [Ca2CoO3]0.62[CoO2]" Physical Review B (to be published)
K. Kurita, M. Yagisawa, and R. Okazaki
"Electrical resistivity and thermopower of hole-doped delafossite CuCoO2 polycrystals" Japanese Journal of Applied Physics60, 013001 (2021). 10.35848/1347-4065/abd448
Published 8 January 2021
R. Okazaki, K. Kobayashi, R. Kumai, H. Nakao, Y. Murakami, F. Nakamura, H. Taniguchi, and I. Terasaki
"Current-induced Giant Lattice Deformation in the Mott Insulator Ca2RuO4" Journal of the Physical Society of Japan89, 044710 (2020). 10.7566/JPSJ.89.044710
Published 25 March 2020
Kanji Kurita, Hokuto Sakabayashi, and Ryuji Okazaki
"Scaling in Transport Coefficients of Hole-doped CuRhO2 Single Crystals" JPS Conference Proceedings30, 011191 (2020).
Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2019) 10.7566/JPSCP.30.011191
Published 19 March 2020
H. Sakabayashi, H. Utagawa, R. Okazaki
"In-plane Anisotropy of Thermoelectric Transport Properties in the Layered Cobaltite [Ca2CoO3]0.62CoO2"
The 5th Asian Conference on Thermoelectrics (ACT5) & The 6th Southeast Asia Conference on Thermoelectrics (SACT6), Thailand (online), AP0020, 17 December 2020.
Yuuka Shiraishi, Kenji Tanabe, Hiroki Taniguchi, Ryuji Okazaki and Ichiro Terasaki
"Interplay between quantum paraelectricity and thermoelectricity in the photo-Seebeck effect in a SrTiO3 single crystal" Journal of Applied Physics126, 045111 (2019). 10.1063/1.5106384
Published 29 July 2019 *Selected as a Featured Article
K. Kurita, H. Sakabayashi, and R. Okazaki
"Correlation in transport coefficients of hole-doped CuRhO2 single crystals" Physical Review B99, 115103 (2019). 10.1103/PhysRevB.99.115103 arXiv:1902.08301
Published 4 March 2019
N. Ito, M. Ishii, and R. Okazaki
"Enhanced Seebeck coefficient by a filling-induced Lifshitz transition in KxRhO2" Physical Review B99, 041112(R) (2019). 10.1103/PhysRevB.99.041112 arXiv:1901.02116
Published 16 January 2019
K. Kurita, H. Sakabayashi, and R. Okazaki
"Scaling in transport coefficients of hole-doped CuRhO2 single crystals"
International Conference on Strongly Correlated Electron Systems 2019, Okayama, Tu-A-15, September 24-28, 2019.
R. Okazaki, S. Ito, K. Tanabe, H. Taniguchi, Y. Ikemoto, T. Moriwaki, and I. Terasaki
"Spectroscopic signature of trimer Mott insulator and charge disproportionation in BaIrO3" Physical Review B98, 205131 (2018). 10.1103/PhysRevB.98.205131 arXiv:1811.00219
Published 16 November 2018
K. Tomiyasu, N. Ito, R. Okazaki, Y. Takahashi, M. Onodera, K. Iwasa, T. Nojima, T. Aoyama, K. Ohgushi, Y. Ishikawa, T. Kamiyama, S. Ohira-Kawamura, M. Kofu, and S. Ishihara
"Quantum Paramagnet Near Spin-State Transition" Advanced Quantum Technologies1, 1800057 (2018). 10.1002/qute.201800057 arXiv:1712.09169
Published 7 October 2018
H. Takahashi, S. Ishiwata, R. Okazaki, Y. Yasui, and I. Terasaki
"Enhanced thermopower via spin-state modification" Physical Review B98, 024405 (2018). 10.1103/PhysRevB.98.024405 arXiv:1807.00551
Published 5 July 2018
Takaaki Sudayama, Hironori Nakao, Yuichi Yamasaki, Youichi Murakami, Shinichiro Asai, Ryuji Okazaki, Yukio Yasui, and Ichiro Terasaki
"Spin State of Co3+ in LaCo1-xRhxO3 Studied Using X-ray Absorption Spectroscopy"
J. Phys. Soc. Jpn. 86, 094701 (2017). 10.7566/JPSJ.86.094701
Published 28 July 2017
T. Okamura, R. Okazaki, H. Taniguchi, Y. Yasui, and I. Terasaki
"Magnetoelectric coupling in the pyrochlore ruthenate Gd2Ru2O7"
J. Phys. Soc. Jpn. 86, 084708 (2017). 10.7566/JPSJ.86.084708
Published 24 July 2017
N. Murashige, F. Takei, K. Saito, and R. Okazaki
"Nonlinear transport associated with spin density wave dynamics in Ca3Co4O9"
Phys. Rev. B 96, 035126 (2017). 10.1103/PhysRevB.96.035126 arXiv:1706.10088
Published 14 July 2017
I. Terasaki, S. Asai, H. Taniguchi, R. Okazaki, Y. Yasui, Y. Ikemoto, and T. Moriwaki
"Optical evidence for the spin-state disorder in LaCo1-xRhxO3"
J. Phys.: Condens. Matter 29, 235802 (2017). 10.1088/1361-648X/aa6ebc
Published 12 May 2017
T. Nagai, H. Takahashi, R. Okazaki, K. Tanabe, I. Terasaki, and H. Taniguchi
"Optical Control of Dielectric Permittivity in LaAl0.99Zn0.01O3-δ"
Appl. Phys. Lett. 110, 172901 (2017). 10.1063/1.4979644
Published 25 April 2017 *Featured in AIP Publishing: "Light Has New Capacity for Electronics"
K. Saito and R. Okazaki
"Electron correlation effect in the thermoelectric oxide Ca3-xSrxCo4O9 single crystals"
Jpn. J. Appl. Phys. 56, 043201 (2017). 10.7567/JJAP.56.043201
Published 27 March 2017
T. D. Yamamoto, R. Yatagai, K. Tanabe, R. Okazaki, H. Taniguchi, Y. Yasui, S. Iguchi, T. Sasaki, and I. Terasaki
"Enhanced thermopower and ferromagnetic fluctuations in Sc-substituted CaRuO3: An experimental study of the Kelvin formula"
APS March Meeting 2017, New Orleans, March 15, 2017