Abstract Body

An intensive study of HgBa₂Ca₂Cu₃O_8+δ(Hg1223), which has the highest superconducting transition temperature (T_c) in cuprates, is required to elucidate the mechanism of high-T_c superconductivity. However, lack of high-quality single crystals blocks progress in the research. Synthesizing high-quality single crystals probably leads to breakthrough in examining the mechanism of high-Tc superconductivity. In this study, we aimed to (1) establish a reproducible method for growing Hg1223 large single crystals and (2) examine their physical properties.

Hg1223 single crystals doped with Re, which stabilizes the crystallization were grown by the self-flux method, in which advantages of previously reported single crystal growth methods^[1]-[4] were adopted. We attempted to identify the optimum conditions for the starting composition and heat treatment through more than 100 experiments. Then, the quality and physical properties of the obtained crystals were evaluated.

Figure 1(a) shows a photograph, XRD, and Laue patterns of the obtained samples. A maximum crystal size was 1 × 1 × 0.04 mm³, as shown in Fig. 1(a). And crystals with the size of ~ 0.8 × 0.8 mm² were obtained with good reproducibility. XRD patterns show (00l) peaks corresponding to Hg1223 (c=15.66 Å) and Laue patterns show four-fold symmetry. These indicate that samples are single crystals of Hg1223. Magnetization measurements (Fig. 1(b)) show the sharp superconducting transition (ΔT_c=3.5 K), the onset transition temperature T_c^on=131.5 K, and the zero-field-cooling volume fraction is over 95% at 90 K. The temperature dependence of the in-plane resistivity ρ_ab (Fig. 1(c)) is T-linear over a wide temperature range, suggesting that the as-grown crystal is of nearly the optimal doping level. The zero-resistance temperature T_c^zero was 128.8 K. Furthermore, the annealing effect on T_c was investigated. T_c^on was decreased to 128 K (overdoped) by oxygen annealing, and to 116 K (underdoped) by reduction annealing. This suggests that the amount of the oxygen content can be changed by annealing to adjust the carrier concentration. In this presentation, we will report details of the single crystal growth and physical property evaluation.

References

[1] C. T. Lin et al, Physica C 300, 141-150 (1998)
[2] S. Ueda et al, Physica C 452, 35-42 (2007)
[3] Bastien Loret et al, Inorg. Chem. 56, 16, 9396–9399 (2017)
[4] L. Wang et al, Phys. Rev. Matter. 2, 123401 (2018)

Acknowledgment

This work was supported by the Japan Society for the Promotion of Science (JSPS); Grant in Aid for Scientific Research (JP 21H01377)