With copper-substituted lead apatite below room temperature, Chinese researchers observe diamagnetic dc magnetization under magnetic field of 25 Oe with remarkable bifurcation between zero-field-cooling and field-cooling measurements, and under 200 Oe it changes to be paramagnetism. A glassy memory effect is found during cooling. Typical hysteresis loops for superconductors are detected below 250 K, along with an asymmetry between forward and backward sweep of magnetic field. The experiment suggests at room temperature the Meissner effect is possibly present in this material.
There were two Chinese teams publicly pursuing LK-99-derived room temperature superconductor. A north China team and south China team. North China team was headed by Hongyang Wang (who lives in Beijing) and south China team was headed by Yao Yao (who lives in Guangzhou). They used different synthesis and different analysis, i.e. north China team used hydrothermal synthesis and used SQUID measurement, while south China team used solid state synthesis and used EPR measurement.
This is a joint paper of both teams. They reproduced results of each other and measured a clear sign of superconductivity. It is near room temperature because they are sure about 250 K but not sure about 300 K.
The biggest feature of the apatite system is the one-dimensional void, which is equivalent to a linear dislocation type defect and is likely to be the only area where carriers accumulate. Therefore, it is very likely that super Guidance only occurs in this area. If this is the case, and superconductivity only occurs here, then they should eliminate the glass phase part, which is 24 O among the 25 O, and a lot of Pb and P parts, because they are not superconducting, so the remaining is the one-dimensional pipe. This is actually very little weight. The proportion of superconductivity is very small, which is actually much more reasonable. This paper is a milestone. It is a starting point for everyone to actively pay attention to the relationship between the structure and performance of this type of system.
At 200 Oe, the material exhibited paramagnetism, and a glassy memory effect was observed during cooling. They resemble behaviors typical of superconductors, including the presence of hysteresis loops below 250 K. Hysteresis loops are critical to assessing how superconductors respond to and retain effects of an applied magnetic field. The direct observation of dc hysteresis, this crucial indicator of superconductivity, remains elusive. It has been observed under microwave conditions but not in direct current measurements. This gap in evidence highlights the ongoing challenges in confirming room-temperature superconductivity in CSLA.
Possible Meissner effect near room temperature in copper-substituted lead apatite
Hongyang Wang1∗, Yao Yao2†, Ke Shi3, Yijing Zhao3, Hao Wu4, Zhixing Wu5, Zhihui Geng6 , Shufeng Ye1, and Ning Chen7
1 Center of Materials Science and Optoelectronics Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, China
2 State Key Laboratory of Luminescent Materials and Devices and Department of Physics,
South China University of Technology, Guangzhou, China
3 Beijing 2060 Technology Co., Ltd, Beijing, China
4 School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan, China
5 Fujian Provincial Key Laboratory of Analysis and Detection Technology for Food safety, College of Chemistry, Fuzhou University, Fuzhou, China
6 School of Engineering, Course of Applied Science, Tokai University, Hiratsuka 2591292, Japan
7 School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
(Dated: January 3, 2024)
Perfect diamagnetism, namely the Meissner effect, serves as one of the fundamental criterions to examine a candidate of superconductor. In order to justify a Meissner effect, one has to first observe a diamagnetic magnetization-temperature (M-T) curve with bifurcation between zero-field-cooling (ZFC) and field-cooling (FC) measurements, along with a superconducting hysteresis magnetization-magnetic field (M-H) loop below critical temperature (Tc) with well-defined critical field (Hc). The copper-substituted lead apatite (CSLA), also named as LK-99, has been claimed as a novel candidate for room-temperature superconductor, but a complete Meissner effect has not been reported up to date. Lee et al. reported a large diamagnetism, but it was stated to stem from Cu2S as addressed by Habamahoro et al. A more important hysteresis loop is still absent in the dc
measurement and has been merely observed in microwave circumstance. There is no doubt the direct observation of dc hysteresis is essential, which turns out to be the main subject of this work.
They used the state-of-the-art synthesis approach, the superconducting component in CSLA possesses pretty small scale, so the critical fields are as weak as several tens Oe. A strong paramagnetic signal may overwhelm possible low-field superconductivity, so the samples should be as pure as possible which may however greatly reduce the doping ratio of coppers and weaken the signals. More importantly, due to the robust memory effect of vortex glass phase, a sample that has been exposed to a strong magnetic field may also hold memory of the magnetization history. In this context, the measurement procedure of magnetic properties must be carefully designed and conducted. They employed the MPMS-3 SQUID to conduct dc magnetization measurements on the samples.
In summary, the diamagnetism in CSLA has been investigated via both M-T curves and hysteresis M-H loops, which can be observed up to 250 K. Given the ZFC-FC bifurcation at above 300 K, they think there is still great chance to observe room-temperature superconductivity. The signals in the sample are still extremely weak, so they have to devote efforts to further synthesizing scalable samples with more active components.
Other Chinese Researchers Detected Superconducting Effects Via Microwave Absorption
There is other experimental evidence from China supporting LK99 with the detection of microwave absorption. All other superconductors have this microwave absorption effect.
Lawrence Berkeley National Labs Has Computational Analysis Supporting LK99
Lawrence Berkeley National Lab researchers use computational methods to describe an approach for optimizing the LK99 material as a superconductor. The National Lab researchers suggest how to improve LK99. Their proposed structure requires substantially higher doping than has been reported experimentally and also with a high degree of site selectivity to facilitate macroscopic cuprate chains. This is not insurmountable as both solid-solution and ordered doping of apatite structures are common. Reported synthesis attempts have been carried out under ambient pressure and using oxygen as the channel species X. Recent theoretical work has identified that pressure, strain, and channel species call all have a strong effect on the site selectivity of the copper dopants.
Original Korean LK99 Team Will Present March 4, 2024
On March 4, 2024, most of the original team of South Korean LK99 Room Temperature and atmospheric pressure superconductors researchers will have a short 12 minute presentation at the American Physical Society conference.
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