Shulou(Shulou.com)11/24 Report--

LK-99 sentenced to death? According to the latest research by Peking University and other institutions, the self-made LK-99 sample has no superconductivity and can be suspended because of its soft ferromagnetism.

LK-99 Room Temperature Superconductivity Event Slapping?

Just today, researchers from Peking University, the University of Chinese Academy of Sciences and other institutions published papers saying that LK-99 exhibits ferromagnetic semi-levitation phenomenon and does not have superconductivity.

Paper Address: arxiv.org/abs/2308.03110

The researchers believe that soft ferromagnetism is sufficient to explain LK-99's semi-levitation in strong vertical magnetic fields. No Meissner effect or zero resistance exists in the sample, so LK-99 sample obtained by experiment has no superconductivity.

At the same time, the Indian National Laboratory also published a paper saying that the LK-99 samples obtained did not have superconductivity at room temperature.

The Center for Condensed Matter Theory (CMTC) at the University of Maryland also forwarded the latest research, saying LK-99 is not a superconductor, even at room temperature (or very low temperatures). It's just a poor material with a very high resistance.

So far, there is no point in fighting facts and speaking with data.

PKU: LK-99 is a ferromagnet PKU and the National University of Science and Technology team successfully synthesized polycrystalline LK-99 ceramic samples by solid state sintering method.

The product is a thick black block 6 mm in diameter and 3 mm in thickness

Energy dispersive X-ray spectroscopy (EDS) showed the presence of Pb, P, Cu, O and S. According to X-ray diffraction results, the main components of the powder were Pb10-xCux(PO4) 6O and Cu2S, consistent with the research of the Korean team.

The team observed the "semi-suspension" phenomenon of the above samples on the Nd2Fe14B magnet.

After magnetic susceptibility measurements of these small pieces and a large piece that did not exhibit semi-levitation, the researchers found that the samples generally contained weak soft ferromagnetic components.

Because the shape of the individual platelets is significantly anisotropic, the team believes that soft ferromagnetism is sufficient to explain the semi-levitation observed in strong vertical magnetic fields.

In addition, since the measurements did not show the Meissner effect or zero resistance, the team concluded that the sample did not exhibit superconductivity.

The magnetization of sample S1, which was not semi-suspended on a Nd2Fe14B magnet, was measured by field cooling (FC) and zero-field cooling (ZFC) measurements.

When the external magnetic field is 10 Oe, the FC and ZFC curves of magnetization versus temperature show positive magnetic moments and obvious branching, as shown in Figure 2 (a).

When the magnetic field is increased to 10 kOe, FC and ZFC M-T curves remain positive and coincident, as shown in Figure 2 (b).

Branching modes in FC and ZFC curves usually occur in ferromagnetic materials, spin glass materials, and superconductors.

However, spin-glass states are more common at lower temperatures, effectively freezing the magnetic moment, while superconducting states typically produce significant negative ZFC magnetization values.

It was this phenomenon that led the team to recognize the existence of ferromagnetic components for the first time.

To further explore ferromagnetic components in the samples, field-dependent magnetization measurements were performed at 100 K and 300 K, as shown in Figure 2 (c).

The external magnetic field increases from 0 to 70 kOe, then decreases from 70 kOe to-70 kOe, and finally increases again from-70 kOe to 70 kOe. Similar behavior was observed at both temperatures.

When the magnetic field increases from 0 to 1500e, the magnetization increases with increasing magnetic field, and then decreases almost linearly with increasing magnetic field, even becoming negative.

This phenomenon indicates that a large amount of insulating components exist in sample S1.

The presence of ferromagnetic phases is further confirmed by the presence of distinct hysteresis loops in the low field data (Figure 2 (d)).

Taking the condition of 100K in Fig. 3 as an example, after subtracting the diamagnetic background, the remaining part shows typical saturation phenomenon above 20 kOe.

Compare some diamagnetic materials with sample S1:

The subtracted diamagnetic susceptibility (~-2 x 10^-6 emu / g) is larger than that of bismuth (-1.6 x 10^-6 emu / g) and water (-10 ^-7 emu / g), but smaller than that of pyrolytic carbon (~ -4 x 10^-6 emu / g).

This indicates that this part of susceptibility is not caused by superconductivity.

So why is it semi-suspended?

The team then measured the magnetic susceptibility of a particle sample, S2, which began vibrating when a Nd2Fe14B magnet approached [see image below].

Because the sample was too small to weigh accurately, the team represented it directly in Figure 4 in units of emu on the vertical axis.

FC and ZFC measurements of susceptibility versus temperature (M-T) curves show positive values similar to those of sample S1 and similar branching structures.

This indicates that S1 and S2 have similar magnetic compositions. However, many other samples do not respond to Nd2Fe14B magnets, some even smaller than S2.

The team believes this may be related to the heterogeneity of the sample, which is likely to reach a semi-suspended state when the sample has the right size, the right composition and the right shape.

Finally, the researchers measured the magnetic susceptibility of sample S3, which showed semi-magnetic levitation on the Nd2Fe14B magnet.

The semi-suspended state of S3 is shown in the figure.

The authors describe it simply in the paper that "semi-levitation is caused by magnetic moments, not by net lifting forces exerted on the sample."

The researchers first performed FC measurements on M-T curves at 100-300 K at 10 Oe.

In the lower graph (a), the susceptibility of the FC curve (black curve) exhibits a significant negative value and hardly changes at temperatures below 300 K.

However, before measuring the ZFC value of M-T, the researchers measured the magnetic field-dependent susceptibility at 100 K, see (b) above.

When the magnetic field increases from 0 to 1500 Oe, the magnetization changes from negative to positive. The black curve in Figure (c) above is a magnified view of this process.

Unlike samples S1 and S2, when the magnetic field increases above 1500 Oe, the susceptibility does not decrease with increasing magnetic field, but increases with a lower slope.

To verify that the samples have zero resistivity, the researchers performed resistance measurements on the particle samples, as shown below.

The results show that the samples have semiconductor transmission behavior, and their resistivity increases gradually with decreasing temperature, and increases by one order of magnitude from 105Ωm to 300 K to 2 K.

In short, the Peking University and the Chinese Academy of Sciences University team believe that the reason why the shape anisotropy samples are semi-suspended should be explained by ferromagnetism.

However, the room-temperature ferromagnetism exhibited in this Pb-Cu-P-O system deserves further study by physicists.

Chinese workers boss evaluation: completion is very low, but Chinese workers boss "Xi Zhixi" said, Peking University this work completion is very low.

A lot of data are not carefully processed, the large field data of the loop line do not coincide, and there are hand-drawn drawings.

Answer address: www.zhihu.com/people/yao326yao

He said it was far-fetched to call it weak ferromagnetism. Because the magnetic field is not saturated to 3T, it does not conform to common sense.

If you must call it ferromagnetic, at most it is formed some small magnetic domains, so the magnetic susceptibility is so small.

In the Peking University study, for a sample with many phases, the most important phase is also suppressed. If a sample is ferromagnetic, superconducting phases are automatically excluded.

In general, ferromagnetism and superconductivity are incompatible. But there are exceptions, such as ferromagnetic superconductors, where the spins are paired in the same direction.

According to the data of Peking University sample, Xi Zhixi said that he did not want to believe that it was a ferromagnetic and diamagnetic mixed phase, but a special spin liquid or even spin glass. Given that there are many triangular lattices inside, spin frustration is possible.

In addition, a previous paper by the Spanish team also found that LK-99 belongs to multiphase heterostructure and is difficult to reproduce.

LK-99 is a multiphase heterostructure with coexisting non-superconducting components. These phases do not produce significant X-ray peaks in XRD, but they still have an impact on electrical resistance and magnetic properties.

To put it bluntly, if you want to reproduce this material now, the results will be very complicated. Because possible superconducting materials are wrapped in nonsuperconducting materials, the resulting phenomenon is confusing.

Even if XRD is the same, it does not mean that the magnetic properties of the samples are the same.

Indian team: LK-99 does not have superconductivity at room temperature Almost at the same time, the Indian National Laboratory also published a paper saying that the resulting LK-99 samples do not have superconductivity at room temperature.

Paper Address: arxiv.org/abs/2308.03544

The basic logic of experimental papers such as India's CSIR National Physics Laboratory is that they follow the Korean team's production process very strictly and produce LK-99 with high purity.

Then through Powder X-ray diffraction (PXRD) and Rietveld refinement to verify that their own materials and the Korean team described in the paper LK-99 is a thing.

Under this premise, the materials in their hands are neither diamagnetic nor superconducting at room temperature!

Specifically, they followed very closely what the Korean team specifically described in their paper.

Cu3P was synthesized by heating at 550 ° C for 48 hours. After further processing, the high-purity powder was heated to 725 ° C in a crucible and annealed for 24 hours to obtain Pb2SO5. LK-99 was then obtained by mixing the two substances in a ratio of 1:1 in a quartz tube and heating for 10 hours.

After refining the data measured by PXRD spectroscopy with Rietveld for the substances in each step of the process, the specific results are shown in the figure below.

The overall data showed that the purity of the samples obtained at each step was very high.

The lattice parameters of LK-99 are shown in the table below:

The team then began by interacting with permanent magnets as the previous teams had done. As shown in the figure below, there is no suspension phenomenon.

Magnetization measurements at 280K show that LK-99 exhibits diamagnetism, but no superconductivity.

Room temperature superconducting revolution, I'm afraid it has to wait a little longer? According to the latest research from Peking University, LK-99 is probably just a ferromagnetic material, which also explains its levitation properties. The revolution in room temperature superconductivity will have to wait another day.

LK-99 was able to float halfway up because it was supported by magnetic moment.

References:

https://arxiv.org/abs/2308.03110

https://arxiv.org/abs/2308.03544

https://www.zhihu.com/people/yao326yao

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