| 研究実績の概要 |
1. I successfully grew FeTe1-xSex and FeSe single crystals by the self-flux method, and vapor transport method, respectively. I also annealed the FeTe1-xSex crystals in the Te-atmosphere to remove the excess Fe in the crystal. The best obtained crystal manifests Tc ~ 14.5 K with a sharp transition width less than 1 K.
2. I studied the transport critical current density in a high-quality FeTe0.6Se0.4 singe crystal. Our previous report shows that Jc calculated by the Bean Model from the magnetic hysteresis loops (MHLs) measurements reaches a value ~ 3×10^4 A/cm2 at 10 K. Such large Jc means that we cannot directly perform the current-voltage measurements on the bulk single crystal since an extremely large current is required. We used the focused ion beam to fabricate a narrow bridge on the single crystal to the width ~680 nm. To avoid damage to the crystal, we applied a rectangular 100 us pulse current through the sample in 3 s. The temperature dependence of the Jc manifests a large value of ~ 1.3×10^6 A/cm2 at 10 K. The value is over 40 times larger than that calculated from the MHLs. Such large transport Jc is discussed in the regime of the departing current density.
3. I studied the anisotropy of FeTe0.6Se0.4 single crystals with different amount of excess Fe by transport measurements including temperature dependences of resistivity, the Hc2, and the transport Jc. In the superconducting state, the anisotropy is smaller than 2, and independent of the amount of excess Fe. While, normal state anisotropy depends on the amount of excess Fe, and ranging from 6 to 50.
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