https://arxiv.org/abs/2308.05778

Current percolation model for the special resistivity behavior observed in Cu-doped ApatiteSince the initial report of the potential occurrence of room-temperature superconductivity under normal pressure [arXiv: 2307.12008], there has been significant interest in the field of condensed matter physics regarding Cu-doped Apatite (Pb10-xCux(PO4)6O). In this study, we performed temperature-dependent resistivity measurements on the synthesized Pb10-xCux(PO4)6O samples. The structure of the sample was confirmed to match the reference literature through X-ray diffraction analysis. Remarkably, we observed four distinct types of resistivity behaviors within samples from the same pellet: (1) A semiconductor-like behavior characterized by a decrease in resistivity as the temperature is lowered. (2) A gradual reduction in resistivity, reaching an exceptionally small value that falls below the resolution limits of our measurement equipment. (3) An abrupt drop in resistivity to a low value at ~ 250 K. (4) An almost linear reduction in resistivity exhibiting a transition at approximately 7 K (possibly associated with Pb). Following a thorough compositional analysis, we proposed a current percolation model, based on the formation of a Cu/Pb current channel, to elucidate the observed special resistivity behaviors. It is important to note that the Meissner effect was not observed in our magnetization measurements. Consequently, we reached the conclusion that the presence of superconductivity in Cu-doped Apatite has yet to be substantiated.arxiv.org




In order to further investigate the physical properties of Pb10-xCux(PO4)6O, we conducted electrical transport and magnetization measurements. Figs. 3(a-d) depict four distinct R-T (resistivity-temperature) curves acquired from various regions of the same sample. Fig. 3(a) reveals a semiconducting behavior, resembling recent findings [9,19]. Interestingly, Fig. 3(b) displays metallic behavior, and an extremely small resistivity emerges below 110 K, as more clearly illustrated in the inset of Fig. 3(b). Data shown in Fig. 3(b) is the same as that presented in our previous report [8], but in the linear plot. In Fig. 3(c), an abrupt drop in resistivity to a small value at ~ 250 K was observed. The enlarge of the low temperature part can be seen in the inset of Fig. 3(c). We also measured the temperature dependence of resistivity under fields up to to 9 T. As the applied magnetic field increasing, the resistivity drop is gradually suppressed. In Fig. 3(d), resistivity manifests a good linear behavior and a sharp transition at 7.1 K, strongly indicating the presence of Pb although it is not detected via XRD. 

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Pb10-xCux(PO4)6O의 물리적 특성을 더 조사하기 위해, 우리는
전기 수송 및 자화 측정. 그림 3(a-d)는 4가지 구별된 R-T를 나타냅니다
(저항-온도) 동일한 샘플의 다양한 영역에서 얻은 곡선. 그림 3(a)에 따르면
최근의 결과와 유사한 반도전적인 행동 [9,19]. 흥미롭게도, 그림 3(b)는 다음과 같이 표시됩니다
더 명확하게, 금속적인 행동, 그리고 극도로 작은 저항성이 110K 이하로 나타납니다
Fig.3(b)의 inset에 예시된 데이터. Fig.3(b)에 제시된 데이터는 우리의 데이터와 동일합니다
이전 보고서 [8]에서 그러나 선형 그림에서. 그림 3(c)에서 작은 값으로 저항률의 급격한 하락
~250 K에서 관찰되었습니다. 저온 부분의 확대는 Fig.의 inset에서 볼 수 있습니다.
3(c). 우리는 또한 9T까지의 필드에서 저항성의 온도 의존성을 측정했습니다
인가 자기장이 증가하면서 저항률 강하가 점진적으로 억제됨. Fig.3(d)에서,
저항성은 7.1K에서 좋은 선형 행동과 급격한 전이를 나타내며, 강하게 표시합니다
XRD를 통해 감지되지 않지만 Pb가 존재합니다.

a16711aa372a76ac7eb8f68b12d21a1d5791f63ff16c

Fig. 3 Temperature dependence of resistivity obtained from four measurements on the different regions of the same sample (a) semiconducting, (b) extremely small resistivity below 110 K, (c) abrupt resistivity drop at ~ 250 K, (d) linear behavior with transition at 7.1 K. (e-j) Currentpercolation model. The brown ellipses depict the Cu/Pb islands, while the blue arrow illustrates the current flow

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그림 3 4가지 측정값으로 얻은 저항률의 온도 의존성
동일한 샘플 (a) 반도전하는 영역, (b) 110K 미만의 극도로 작은 저항률, (c)
~250K에서 급격한 저항 감소, (d) 7.1K에서 전이되는 선형 거동(e-j) 전류 퍼콜레이션 모델. 갈색 타원은 Cu/Pb 섬을 나타내고 파란색 화살표를 나타냅니다
시류


a16711aa372a6ae864afd19528d52703df7a3b7f7f4cca

Fig. 4 The magnetization of sample (a) The magnetization versus temperature (M-T) at a external magnetic field of 20 Oe, (b) M-T at an external magnetic field of 10 kOe, (c) M-H loop at different temperatures, (d) enlarge view of M-H loop at the low field. 

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Fig.4 시료의 자화 (a) 외부 자기장 20 Oe에서의 자화 대 온도 (M-T), (b) 외부 자기장 10 kOe에서의 M-T, (c) 다른 온도에서의 M-H 루프, (d) 낮은 자기장에서의 M-H 루프의 확대도.


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