2007 Fiscal Year Final Research Report Summary
Research for Superconducting Pairing Symmetry in Unconventional Superconductors by Geometry Effects
| Project/Area Number |
18540329
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Condensed matter physics II
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| Research Institution | Shinshu University (2007)
Hokkaido University (2006) |
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Principal Investigator |
TENYA Kenichi Shinshu University, Faculty of Education, Associate Professor (70261279)
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| Project Period (FY) |
2006 – 2007
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| Keywords | spin-triplet superconductivity / unconventional superconductivity / Little-Parks oscillation / magnetization measurements |
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| Research Abstract |
From several experimental results, the layered ruthenate Sr_2RuO_4 is evidenced to be a spin-triplet superconductor with the degenerate chiral d-vector. In the spin-triplet superconductors with chiral d-vectot dynamics on the two superconducting domains with opposite chiralities is expected to be experimentally observed. In order to investigate the chiral superconducting characteristics as well as the vortex-pinning properties, the measurements of Little-Parks oscillation and static magnetization on the single crystalline samples Sr_2RuO_4 have been performed in the field direction parallel to the [001) axis.
For the Little-Parks oscillation measurement, tiny single crystalline samples of Sr_2RuO_4 with small holes were prepared by using FIB. We succeed in observing the phenomena that the resistivity of the samples periodically oscillates with field, and we are checking whether this oscillation is really intrinsic to the superconductivity or not.
Anomalous pinning features are found at weak fields in the magnetization curves in the superconducting mixed state: Tiny flux-jumps successively appear around zero-field at temperature up to at least 0.2 K. At higher temperatures, a small peak of the hysteretic magnetization is observed below 0.1 kOe, which is so-called second magnetization peak (SMP). The magnitude of the hysteretic magnetization is strongly dependent on (independent of) the field-gradient in the field region below (above) the field HSMP where the SMP appears. These phenomena can be explained by assuming that the superconducting &domains easily move under the field-gradient or super current flow, leading to the reduction of the effective pinning-force at the domain boundaries. Another possible origin of the anomalous magnetization features around HSMP is the topological transition in the vortex-state from Bragg-glass to vortex-glass, occasionally observed in "super-clean" type II superconductors.
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