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PreprintarXiv licencearXiv

Enhanced Critical Currents and Irreversibility Fields in YBa2Cu4O8 Films through Ca-Substitution

  • Jiangteng Liu
  • Shuhei Funaki
  • Yuki Ogimoto
  • Bryan Zhang
  • Ryoya Nagaura
  • Ryuji Yoshida
  • Takeharu Kato
  • Masashi Miura
  • Serena Eley
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Abstract

The intrinsic carrier concentration of superconducting materials may not be optimal, and different superconducting properties may have distinct optimal doping levels. Here, we show that Ca substitution increases the hole concentration in intrinsically underdoped epitaxial (Y1−xCax)Ba2Cu4O8 (YCa124) films with x ≤ 0.10, driving YCa124 toward optimal doping, increasing Tc and Jc. At 40 K, 10% Ca doping increases Jc by factors of 2.4 and 10 at 0.03 and 6 T, respectively, compared with the undoped film. The field dependence of Jc follows Jc ∝ B−0.5, independent of Ca content, indicating that Ca substitution does not alter the dominant pinning mechanism. This field dependence is consistent with pinning by planar Y-125 stacking-fault intergrowths observed by electron microscopy. In addition, Ca substitution slows thermally activated vortex motion (creep) at T ≳ 15 K, while at lower temperatures the creep rate S shows an unusual decrease with increasing field. Finally, we consider how doping tunes the upper bound on Jc, set by the depairing current density Jd, and the lower bound on creep, set by the Ginzburg parameter Gi. We find positive correlations between Jc and Jd, and between S and Gi, and compare them with trends across a broad range of superconductors.

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Cite

BibTeXRIS
BibTeX
@misc{liu2026enhanced,
  title = {{Enhanced Critical Currents and Irreversibility Fields in YBa$_2$Cu$_4$O$_8$ Films through Ca-Substitution}},
  author = {Jiangteng Liu and Shuhei Funaki and Yuki Ogimoto and Bryan Zhang and Ryoya Nagaura and Ryuji Yoshida and Takeharu Kato and Masashi Miura and Serena Eley},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2609.36402},
  eprint = {2609.36402},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.36402},
}
RIS
TY  - UNPB
TI  - Enhanced Critical Currents and Irreversibility Fields in YBa_2Cu_4O_8 Films through Ca-Substitution
AU  - Jiangteng Liu
AU  - Shuhei Funaki
AU  - Yuki Ogimoto
AU  - Bryan Zhang
AU  - Ryoya Nagaura
AU  - Ryuji Yoshida
AU  - Takeharu Kato
AU  - Masashi Miura
AU  - Serena Eley
PY  - 2026
DA  - 2026/10/13
PB  - arXiv
DO  - 10.48550/arxiv.2609.36402
UR  - https://arxiv.org/abs/2609.36402
AB  - The intrinsic carrier concentration of superconducting materials may not be optimal, and different superconducting properties may have distinct optimal doping levels. Here, we show that Ca substitution increases the hole concentration in intrinsically underdoped epitaxial (Y_1−xCa_x)Ba_2Cu_4O_8 (YCa124) films with x ≤ 0.10, driving YCa124 toward optimal doping, increasing T_c and J_c. At 40 K, 10% Ca doping increases J_c by factors of 2.4 and 10 at 0.03 and 6 T, respectively, compared with the undoped film. The field dependence of J_c follows J_c ∝ B^−0.5, independent of Ca content, indicating that Ca substitution does not alter the dominant pinning mechanism. This field dependence is consistent with pinning by planar Y-125 stacking-fault intergrowths observed by electron microscopy. In addition, Ca substitution slows thermally activated vortex motion (creep) at T ≳ 15 K, while at lower temperatures the creep rate S shows an unusual decrease with increasing field. Finally, we consider how doping tunes the upper bound on J_c, set by the depairing current density J_d, and the lower bound on creep, set by the Ginzburg parameter G_i. We find positive correlations between J_c and J_d, and between S and G_i, and compare them with trends across a broad range of superconductors.
ER  -