| 研究実績の概要 |
Magneto-optical Kerr effect has been frequently used to study the magnetic materials. When a linearly polarized light is incident onto a magnetic sample, the polarization of the reflected light would be rotated and the rotation angle is called Kerr angle. This effect is not only sensitive to magnetism, but also other time reversal symmetry breaking phenomena. Therefore, it can be a powerful method to study unconventional superconductivity and topological features. For example, the Kerr angle measurement unambiguously demonstrated the chiral superconductivity in Sr2RuO4 (Xia et. al, PRL 97, 167002).
In this project, we have successfully constructed an all-fiber Sagnac interferometer to measure the Kerr angle, which is insensitive to vibration and flexible to be integrated with other techniques. We are able to measure Kerr angle at low temperature (2 K) and high magnetic field (11 T) with a sensitivity of 1 micro-rad. The magnetic SrRuO3/SrTiO3 epitaxial film was measured as a demonstration of principles. A large rise of Kerr angle was observed at 147 K and hysteresis loop was detected in field sweep at lower temperature. This is consistent with the ferromagnetic transition reported in this material. In an attempt to investigate superconductivity, we take Nb as a test sample. The Kerr angle does not change across Tc at zero field but increases below Tc when magnetic field is applied, indicating the vortex pinning in superconducting state. With these results, we believe our technique will aid in the research of unconventional superconductivity.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
We are currently optimzing our optics and electronics setup to improve the data quality. The main source of optical background signal is the Faraday effect of the lens. We are trying different materials and dimensions of the lens to minimize the background. Meanwhile, we are building a non-gas-flow probe to improve the stability at low temperature.
In terms of materials, we are investigating unconventional superconductivity in Fe-based superconductors and Sr2RuO4. We believe our technique can elucidate the gap symmetry and chirality of these samples. We are also exploring other novel materials such as new Kagome lattice materials AV3Sb5, which exhibit exotic magnetic properties and possible unconventional superconductivity. Preliminary data has been obtained and more experiments will be done.
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| 今後の研究の推進方策 |
In the future, we will extend our experimental conditions to lower temperature using dilution fridge and vector magnet. We intend to develope the intensity modulation technique together with phase modulation to further reduce the noise and improve the stability.
Furthermore, in order to explore rich phases of a material, we will integrate the Kerr angle measurement with uniaxial strain device so that we can control the properties, such as nematicity, of the sample. Uniaxial strain as a tuning parameter will enable us to study the interplay between the nematicity and superconductivity.
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