2019 Fiscal Year Research-status Report
Study of the high temperature superconductivity of iron-chalcogenide superconductors via combining the micro-structure fabricating and ion-gating technique
| Project/Area Number |
19K14661
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| Research Institution | Aoyama Gakuin University |
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Principal Investigator |
孫 悦 青山学院大学, 理工学部, 助教 (30824180)
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| Project Period (FY) |
2019-04-01 – 2022-03-31
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| Keywords | Fe(Te,Se) / micro-fabrication / superconductivity / critical current density / ion-gating |
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| Outline of Annual Research Achievements |
We have successfully fabricated a series of micro-bridges along the c-axis with a square-micrometer cross-section in high-quality Fe(Te,Se) thin flakes. With such narrow bridges, we successfully achieved the depairing critical current density (Jc), which reaches a very large value (2MA/cm^2), about one order of magnitude larger than the depinning Jc. It is the first report of depairing Jc down to ~0.3 Tc in iron based superconductors. The achievement was published in Phys. Rev. B 101, 134516.
We studied the superconducting and normal state anisotropies of Fe(Te,Se) single crystals with different amount of excess Fe in fabricated in-plane and out-of-plane bridges. Our research revealed that the discrepancy between the superconducting and normal state anisotropies of Fe(Te,Se) is due to the anisotropic scattering from the interstitial excess Fe. The results have been summarized and prepared to be submit.
We have grown a series of Fe(Te,Se) singe crystals with different ratio of Te/Se, and improved their quality by annealing with O2 and Te atmosphere. We also successfully prepared Fe(Te,Se) thin flakes with thickness ranging from several hundred nm to ~ 50 nm by scotch tape cleaving, which will be used for making electric-double layer (EDL) transistors. We have improved our refrigerator (LTS-205D-TL-50）to make it capable for ion-gating, and have tested the gating on a Fe(Te,Se) thin flake with the thickness of 500 nm fabricated by focus ion beam (FIB).
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
We also already obtained high-quality Fe(Te,Se) single crystals for the current research, and successfully reduced the crystal's thickness to ~ 50 nm by scotch tape cleaving, which is suitable for making electric-double layer (EDL) transistors. For the micro-fabrication, we have made thin flakes with thickness less than 500 nm by FIB, and also made a narrow c-axis bridge. Those thin flakes and c-axis bridges could be used for making EDL transistors. We also improved our measurement equipment, and tested the gating on a Fe(Te,Se) thin flake. In summary, we have finished the proposed processes of crystal preparing, micro-fabrication of thin flakes and narrow bridges, and the preparation for ion-gating.
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| Strategy for Future Research Activity |
In the testing experiments of ion-gating on a Fe(Te,Se) thin flake with the thickness of 500 nm fabricated by FIB, we found out that the carrier doping effect is relatively weak, which may be due to the fact that the crystal is still too thick. Therefore, we will turn to make EDL transistors on the thin flakes prepared by scotch tape cleaving, which is with thickness ~50 nm. In this year, we will focus on the transport measurements on the micro-structure fabricated Fe(Te,Se) EDL device under magnetic field. We plan to measure the Hall effect, magnetoresistance to investigate the carrier density and band structure evolution with gating. We also plan to measure the deparing current density on the narrow bridge-EDL devices, which will provide the information of gap structures.
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| Causes of Carryover |
The travel expenses for attending conference in this year was covered by the university. We cannot buy the liquid Helium due to the helium shortage in Japan. We turned to use the refrigerator to do the measurement, so the expense for liquid Helium was saved. Those money will be used in the next year in article costs.
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