Welcome to the website of the Quantum Materials Lab, Department of Physics, Graduate School of Science at Kyoto University!
The academic staff members of our group are Yoshiteru Maeno (Professor), Kenji Ishida (Professor), and Shingo Yonezawa (Assistant Professor).
Our main research activities are the experimental investigation of Superconductivity and Magnetism.
The structure of the superconducting gap, which is one of the most fundamental pieces of information of a superconductor, has been unresolved for more than 30 years in the case of the first-discovered organic superconductors: the TMTSF-based molecular conductors. Overcoming experimental difficulties, we succeeded in the first mapping of the positions of the zeros on the gap of (TMTSF)2ClO4 from our precise field-angle resolved calorimetory and in proposing possible gap structures. Generally speaking, the structure of the gap is closely related to the mechanism of superconductivity in a material. Thus, our mapping provides a new clue to unveil the mechanism of unconventional superconductivity in the TMTSF systems, and to investigate similarities to other superconductors such as high-transition-temperature copper oxides or iron pnictides. In addition, we determined the thermodynamic phase diagram of this material for the first time for all three principle field directions. This result proposes existence of two regions: a long-range ordered superconducting state in low magnetic fields and an interesting short-range ordered or fluctuating superconducting state in higher fields. This result is published in the Rapid Communication section of Physical Review B.
From detailed angle-resolved NMR and Meissner measurements on a ferromagnetic (FM) superconductor UCoGe (TCurie~ 2.5 K and TSC ~ 0.6 K), we show that superconductivity in UCoGe is tightly coupled with longitudinal FM spin fluctuations along the c axis.We found that magnetic fields along the c axis (H || c) strongly suppress the FM fluctuations and that the superconductivity is observed in the limited magnetic-field region where the longitudinal FM spin fluctuations are active. These results, combined with model calculations, strongly suggest that the longitudinal FM spin fluctuations tuned by H || c induce the unique spin-triplet superconductivity in UCoGe. This is the first clear example that FM fluctuations are intimately related with superconductivity.
We have published a review article on superconductivity in Sr2RuO4, which is one of the leading candidates of the spin-triplet superconductor. This review summerizes developments in research of this oxide since the previous review (Mackenzie and Maeno, Rev. Mod. Phys. 2004) was published. Accumulating evidence for the spin-triplet superconductivity in this oxide is described in detail. In addition, unconventional superconducting phenomena originating from the unconventional superconducting state are presented. In particular, recent recognition of Sr2RuO4 as a "topological superconductor" is explained. This review was published as a part of the Special Topics "Recent Developments in Superconductivity" of the Journal of the Physical Society of Japan.
We report that nonmagnetic heavy-fermion (HF) iron oxypnictide CeFePO with two-dimensional XY-type anisotropy shows a metamagnetic behavior at the metamagnetic field HM ~ 4 T perpendicular to the c axis and that a critical behavior is observed around HM. Although the magnetic character is entirely different from that in other Ce-based HF metamagnets, HM in these metamagnets is linearly proportional to the inverse of the effective mass, or to the temperature where the susceptibility shows a peak. This finding suggests that HM is a magnetic field breaking the local Kondo singlet, and the critical behavior around HM is driven by the Kondo breakdown accompanied by the Fermi-surface instability.
Many members of our laboratory are going to present their recent study at the conference for yound reserachers about topological quantum phenomena in Nov. 1-5, 2011, Laforet Biwako, Shiga. Yonezawa(Assistant Professor) is going to present at The 9th International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets (ISCOM 2011) in Sep. 25-30, 2011, Poland.
Kitagawa(D2) and Hattori(D1) are going to present at the 2nd autumn school for young researchers about Heavy Electrons in Sep. 26-30, 2011, Koyasan University, Wakayama.
Many members of our laboratory are going to present their recent study at the annual meeting of the Japanese Physical Society 2011 autumn meeting in Sep. 21-24, 2011, University of Toyama, Toyama.
Nakamura(D3) is going to present at the 7th national conference on topological phenomena in Sep. 8-10, 2011, Nagoya University, Aichi.
Maeno(Prof), Kitagawa(D2), Eguchi(D2), Taniguchi(D1), Iye(D1) and Hattori(D1) are going to present at International Conference on Strongly Correlated Electrons Systems 2011 in August 29 - September 3, 2011, Chambridge, UK.
Nakamura(D3) and Ishikawa(M2) are going to present their recent study at 26th International Conference on Low Temperature Physics in August 10-17, 2011, Beijing, China .
The website of the International Workshop "Novel Spin Pairing 2009 (NSP2009)" is now open. This meeting is a satellite conference of "The 9th International Conference on Materials and Mechanisms of Superconductivity (M2S-IX)" and will be held at Kyoto University in September 2009.
Many members of our laboratory are going to present their recent research at the 64th annual meeting of the Japanese Physical Society in March 2009 at the Rikkyo University in Toyko. A list of the presentations can be found here.