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.
One of the remaining issues concerning the spin-triplet superconductivity of Sr2RuO4 is the strong limit of the in-plane upper critical field Hc2 at low temperatures. In this study, we clarified the dependence of Hc2 on the angle theta between the magnetic field and the ab plane at various temperatures, by precisely and accurately controlling the magnetic field direction. We revealed that, although the temperature dependence of Hc2 for |θ|=5º is well explained by the orbital pair-breaking effect, Hc2(T) for |θ|<5º is clearly limited at low temperatures. We also revealed that the Hc2 limit for |θ|<5º is present not only at low temperatures but also at temperatures close to Tc. These features may provide additional hints for clarifying the origin of the Hc2 limit. Interestingly, if the anisotropic ratio in Sr2RuO4 is assumed to depend on temperature, the observed angular dependence of Hc2 is reproduced better at lower temperature with an effective-mass model for an anisotropic three-dimensional superconductor. We discuss the observed behavior of Hc2 based on existing theories. This result is published in Physical Reveiw B.
While the superconducting transition temperature Tc of Sr2RuO4 is 1.5 K, its onset Tc is enhanced as high as 3 K in the Sr2RuO4/Ru eutectic system, which is often referred to as the 3-K phase. We have investigated effects of uniaxial pressure on the non-bulk superconductivity in the 3-K phase. While Tc of pure Sr2RuO4 is known to be suppressed by hydrostatic pressure, a large enhancement of the superconducting volume fraction of the 3-K phase was observed for both out-of-plane and in-plane uniaxial pressures. Especially, under the in-plane pressure, the shielding fraction at 1.8 K of only less than 0.5% at 0 GPa exceeds 40% at 0.4 GPa. Such a large shielding fraction suggests that under the uniaxial pressure interfacial 3-K phase superconductivity penetrates deep into the bulk of Sr2RuO4. The present finding provides a significant implication to the unresolved origin of the enhancement of Tc to 3 K in the Sr2RuO4/Ru eutectic system. This result is published in Journal of the Physical Society of Japan.
We report 31P and 139La NMR studies of (La0.87Ca0.13)FePO, which is a family member of the recently discovered superconductor LaFeAs(O1-xFx). In the normal state, Knight shift and nuclear spin-lattice relaxation rate divided by T (1/T1T) show that a Fermi-liquid state with moderate ferromagnetic fluctuations emerges below 30 K. From 1/T1T of 31P and 139La, a quasi-two- dimensional electronic structure is suggested, in which the FeP layer is more conductive than the LaO layer. In the superconducting (SC) state, although a clear Meissner signal was observed, 1/T1T increases below Tc, in contrast to a decrease of 1/T1T due to the opening of a SC gap, suggesting that novel low-energy spin dynamics develop in the SC state. This result is published in Physical Review Letters.
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.