• 한국세라믹학회지
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• 제34권2호
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• pp.139-144
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• 1997

결정학적으로 T' 구조인 Nd2-xCexCuO4-$\delta$ 회토류 구리산화물 초전도체는 지금까지 매우 복잡한 미세구조를 지닌 것으로써 잘 알려져 있다. 이 구리산화물 초전도체가 초전도 특성을 띠려면, Nd3+ 이온이 Ce4+ 이온에 의해 소량 치환되고 동시에 산소환원이 필요하다. 본 연구에서는 투과전자현미경의 수렴성 전자회절(CBED)패턴을 이용하여 Nd2-xCexCuO4-$\delta$ 의 Ce 미량 첨가와 미량의 산소환원에 따른 결정구조의 전이 발생 여부에 관하여 고찰하였다. 세 가지의 서로 다른 시편 Nd2CuO3,Nd1.85Ce0.15CuO4 와Nd1.85Ce0.15CuO3.965을 고상소결에 의하여 만들어 이들 각각 시편에 대한 CBED패턴을 주사투과전자현미경(STEM)으로 관찰하였다. 그리고 실험에 의하여 얻은 이들 HOLZ선들과 컴퓨터 계산에 의해 그려진 이론적인 HOLZ선들과 비교하는 방법에 의하여 Nd1.85Ce0.15CuO4의 격자상수를 구하였다.

• 한국초전도ㆍ저온공학회논문지
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• 제16권1호
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• pp.1-5
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• 2014

We calculated the resonance tunneling energy band in the BCS gap for Type-II superconductor in which periodic potential is generated by external magnetic flux. In this model, penetrating magnetic flux was assumed to be in a fixed lattice state which is not moving by an external force. We observed the existence of two subbands when we used the same parameters as for the $Nd_{1.85}Ce_{0.15}CuO_X$ thin film experiment. The voltages at which the regions of negative differential resistivity (NDR) started after the resonant tunneling ended were in a good agreement with the experimental data in the field region of 1 T - 2.2 T, but not in the high field regions. Discrepancy occurred in the high field region is considered to be caused by that the potential barrier could not be maintained because the current induced by resonant tunneling exceeds the superconducting critical current. In order to have better agreement in the low field region, more concrete designing of the potential rather than a simple square well used in the calculation might be needed. Based on this result, we can predict an occurrence of the electromagnetic radiation of as much difference of energy caused by the 2nd order resonant tunneling in which electrons transit from the 2nd band to the 1st band in the potential wells.

• Progress in Superconductivity
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• 제11권2호
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• pp.83-86
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• 2010

There are theoretical and experimental evidences for the pseudo-gap in electron doped cuprates being due to interaction between electrons and anti-ferromagnetism(AFM). A remaining issue is on how AFM correlates with pseudo-gap, and eventually with superconductivity. To elucidate the issue, we have performed temperature dependent angle-resolved photoemission studies of an e-doped cuprate superconductor $Sm_{2-x}Ce_xCuO_4$(SCCO) x=0.18 at 20K and 150K. In the case of $Nd_{2-x}Ce_xCuO_4$, the most well known e-doped cuprate, pseudo-gap disappears at around 100 K for x=0.17. Our experimental result reveals that the pseudo-gap of SCCO exists even at 150K for x=0.18. This result implies that the AFM of SCCO survives even in x=0.18, which agrees with previously reported phase diagram of SCCO. Yet, the superconductivity disappears around x=0.18 for both NCCO and SCCO in spite of the difference in the magnetic order. This result sheds a light on the disappearance of superconductivity on the over-doped side.