Abstract Body

The effect of pressure on the superconducting properties of high-T_c cuprate superconductors remains a complex and unresolved issue. So far, it has been reported that the T_c in Hg-1223 increases up to 153 K (zero resistivity) under high pressure, which is an increase in T_c that cannot be achieved by carrier doping. Therefore, if we can clarify what kind of material parameters are affected by pressure, we will be able to approach the origin of high-T_c superconductivity.

Then we measured the pressure effects in Tl-based cuprate superconductors, which have high T_c (>130 K) and a crystal structure similar to that of Hg-based cuprates (Fig.1).

Since an anomalous annealing effect has been reported in Tl-1223[3], we also measured the annealing effects in a high purity samples of Tl-based cuprates.

First, polycrystalline samples of Tl-based cuprates were prepared by high-pressure synthesis. Next, the carrier doping level was adjusted by reductive annealing in nitrogen flow (Fig.2). The change in lattice parameters due to annealing were also measured. Finally, resistivity measurements under high pressure (Fig.3) were performed using a cubic-anvil-type apparatus. This apparatus has the advantage of being able to apply high pressure (>10 GPa) while having excellent hydrostatic pressure.

 We were able to obtain samples with a variety of T_c by annealing. The change of superconducting properties that seemed to depend on the number of CuO₂ planes were observed by resistivity measurements under high pressure.

References

[1] Takahashi, H. (2006). High Pressure Technology and High Temperature Superconductivity Research in Materials Science. Nihon University, College of Humanities and Sciences.
[2] N. Takeshita et al., J. Phys. Soc. Jpn. 82(2013) 023711.
[3] A. Iyo, M. Hirai, et al. Physica C 388-389(2003) 365-366.

Acknowledgment

I would like to express my gratitude to the co-authors for their continuous and generous guidance and support in this research.