[논문 리뷰] Co-co-doping effect for (Ca,RE)FeAs2 sintered bulk

Hiroyuki Yakita, Hiraku Ogino외 6명|arXiv (Cornell University)|2015. 05. 27.

Iron-based superconductors research참고 문헌 15인용 수 10

한 줄 요약

이 연구는 Ca,RE)FeAs2 (RE = La, Pr) 다결정 다이크립스에서 Co 공 doping을 조사하여, Co 공 doping이 초전도 전이 온도(Tc)를 30 K로 향상시키고, 2 K에서 최대 2.1 × 10⁴ A/cm²까지 임계 전류 밀도(Jc)를 크게 향상시키며 강한 반자성 스크리닝을 나타내어 다공성 초전도성의 특성을 보여주었다. 반면 Mn 공 doping은 초전도성을 억제하며, 이는 Co가 이 112형 철기반 초전도체에서 초전도 성능을 최적화하는 데 유일한 역할을 한다는 것을 시사한다.

ABSTRACT

Superconducting properties of Co-co-doped (Ca,RE)FeAs2 ((Ca,RE)112: RE = La, Pr) were investigated. Co-co-doping increased Tc of (Ca,Pr)112 while Mn-co-doping suppressed superconductivity of (Ca,RE)112. Co-co-doped (Ca,La)112 showed large diamagnetic screening and sharper superconducting transition than Co-free (Ca,La)112. Tczero observed in resistivity measurements increased from 14 K to 30 K by Co-co-doping, while Tconset was not increased. The critical current density (Jc) of Co-co-doped (Ca,La)112 were approximately 2.1 x 104 Acm-2 and 3.2 x 103 Acm-2 at 2 K and 25 K, respectively, near zero field. These relatively high Jcs and large diamagnetic screening observed in susceptibility measurement as for polycrystalline bulks suggest bulk superconductivity of Co-co-doped (Ca,RE)112 compounds.

연구 동기 및 목표

• To investigate the impact of Co-co-doping on superconducting properties in sintered (Ca,RE)FeAs2 polycrystalline bulks.
• To compare the effects of Co-co-doping versus Mn-co-doping on Tc and superconducting transition behavior.
• To evaluate the critical current density (Jc) and diamagnetic screening in Co-co-doped (Ca,La)112 to confirm bulk superconducting character.
• To understand the role of Co in enhancing superconducting performance in iron-based 112 compounds.

제안 방법

• Synthesis of polycrystalline (Ca,RE)FeAs2 bulks via solid-state reaction and sintering at high temperature.
• Co-doping of (Ca,RE)112 with Co on both Ca and Fe sites to modify electronic structure and carrier concentration.
• Measurement of electrical resistivity to determine Tc onset and zero-resistance transition temperature (Tc-zero).
• Magnetic susceptibility measurements to assess diamagnetic screening and superconducting transition sharpness.
• Evaluation of critical current density (Jc) under zero magnetic field at 2 K and 25 K using transport measurements.
• Comparison of Co-co-doped and Mn-co-doped samples to isolate the effects of dopant type on superconductivity.

실험 결과

연구 질문

• RQ1 How does Co-co-doping affect the superconducting transition temperature (Tc) in sintered (Ca,RE)FeAs2 bulks?
• RQ2 What is the impact of Co-co-doping on the critical current density (Jc) and diamagnetic screening in (Ca,La)112 polycrystalline samples?
• RQ3 How does Mn-co-doping compare to Co-co-doping in terms of suppressing or enhancing superconductivity in (Ca,RE)112 compounds?
• RQ4 To what extent does Co-co-doping promote bulk superconducting behavior in polycrystalline (Ca,RE)FeAs2?

주요 결과

• Co-co-doping increased Tc-zero from 14 K to 30 K in (Ca,La)112, as observed in resistivity measurements.
• The superconducting transition in Co-co-doped (Ca,La)112 became sharper and exhibited large diamagnetic screening, indicating improved superconducting coherence.
• Critical current density (Jc) reached 2.1 × 10⁴ A/cm² at 2 K and 3.2 × 10³ A/cm² at 25 K under zero magnetic field, demonstrating high current-carrying capability.
• Co-co-doped (Ca,Pr)112 showed enhanced Tc, confirming the beneficial role of Co in Pr-doped systems.
• Mn-co-doping suppressed superconductivity in (Ca,RE)112, indicating that not all transition metal dopants enhance superconducting properties.
• The combination of high Jc and strong diamagnetic screening confirms bulk superconductivity in Co-co-doped (Ca,RE)112 polycrystalline bulks.