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

This article comes from the official account of Wechat: back to Park (ID:fanpu2019), by Liu Miao and Lu Tenglong

Recently, there has been a heated discussion about the room temperature superconducting LK-99 of the South Korean team. In addition to many research groups around the world trying to reproduce the experiment, a number of theoretical calculation articles have been published on the preprint website. These papers believe that the doping of Cu causes the transition from insulator to conductor, which theoretically implies that the material may achieve superconductivity at room temperature. But can the density functional calculations they use prove superconductivity? The answer is no.

Written by Liu Miao, Lu Tenglong (Institute of Physics, Chinese Academy of Sciences)

Room temperature superconductivity is a discovery that can be realized "for the first time" in the physics circle every year. If you include the Lu-H-N of the Ranga Dias team at the University of Rochester in March, room temperature superconductivity has been discovered twice this year.

Whether LK-99 has room temperature superconductivity has become a hot topic by all walks of life.

Not to mention the experimental proof of LK-99. Up to now, at least five related density functional theory (DFT) calculation articles have been posted on arXiv in a few days. The most exciting part of the study of room temperature superconducting calculation is the blowout of the paper.

The five DFT papers are:

First-principles study on the electronic structure of Pb10-xCux (PO4) 6O (xylene 0,1)

ArXiv:2307.16040 (29 Jul 2023)

Origin of correlated isolated flat bands in copper-substituted lead phosphate apatite

ArXiv:2307.16892 (31 Jul 2023)

Electronic structure of the putative room-temperature superconductor Pb9Cu (PO4) 6O

ArXiv:2308.00676 (1 Aug 2023)

Pb-apatite framework as a generator of novel flat-band CuO based physics, including possible room temperature superconductivity

ArXiv:2308.00698 (1 Aug 2023)

Theoretical insight on the LK-99 material

ArXiv:2308.01135 (2 Aug 2023)

Five months ago, Lu-H-N room temperature superconductivity was reported and hammered in the ring. Not long ago, we even found out the irrefutable evidence that the data of the PRL paper of Dias team was falsified in 2020. In contrast, in this LK-99 event, many DFT papers have the same point of view, all supporting the possible existence of superconductivity in LK-99. Dias is probably going to cry.

The results of five DFT calculations show that Pb9Cu (PO4) 6O (chemical formula of LK-99) has a flat energy band passing through the Fermi surface. The authors generally believe that the doping of Cu leads to the transition from insulator to conductor, and then boldly infer that LK-99 may have superconducting properties.

For example, Sinead M. Griffin of Lawrence Berkeley National Laboratory said bluntly: "the calculations presented here suggest that Cu substitution on the appropriate (Pb (1)) site displays many key characteristics for high-TC superconductivity" (calculation shows that after Cu replaces a certain Pb atom, the system shows several key properties of high temperature superconductivity).

Although the tone of these analyses sounds specious, the implications can't help but make people wonder.

So is it possible to prove the room temperature superconductivity of LK-99 by DFT calculation?

The answer is no!

First of all, the physical mechanism of high temperature superconductors is not clear, still less can it be solved by DFT. Although the superconducting phase transition of conventional superconductors can be predicted by calculating the electron-phonon interaction, a recognized method for calculating the superconducting phase transition of high temperature superconductors has not been developed. Therefore, none of the five DFT papers can provide direct theoretical support for LK-99 high temperature superconductors or room temperature superconductors.

Secondly, can the energy band near the Fermi surface be interpreted as superconductivity? Obviously not.

The energy band of the conductor passes through the Fermi surface, and the superconductor is a kind of conductor, so the energy band of the superconductor also passes through the Fermi surface, but it is logically wrong to interpret the energy band passing through the Fermi surface as suspected superconductivity. This is like a car with four wheels, an electric car is a kind of car, so an electric car also has four wheels, because when you see a vehicle with four wheels, you think it is an electric car.

Finally, how did the flat belt near Fermi noodles come from? Is it evidence of a strong connection? Of course not.

(1) for any doping system, the impurity energy level calculated from DFT appears to be a relatively flat band. But this is an impurity energy level, not an energy band, let alone a flat band. The lower the doping concentration, the flatter the "band" looks.

Taking S or Si doped in black phosphorus as an example (figure 1), the lower the impurity concentration is, the flatter the band of impurity energy level is. It is consistent with the phenomenon in LK-99 's paper, so will black phosphorus doped with S or Si become high temperature superconductor?

Fig. 1 taking S or Si doped in black phosphorus as an example, the lower the impurity concentration is, the flatter the band of impurity energy level is. It is consistent with the phenomenon in LK-99 's paper, so will black phosphorus doped with S or Si become high temperature superconductor? [the picture is taken from Beilstein J. Nanotechnol. 2019, 10993-1001.] (2) if any semiconductor or insulator is doped, if the impurity energy level is between bands, the Fermi surface falls on the impurity energy level according to the definition of DFT energy band in this paper.

In fig. 2, the impurity energy level doped with V and V in AlN appears to be a "platform". After doping, the Fermi surface moves near the impurity energy level.

Fig. 2 the impurity energy level doped with V and V in AlN appears to be a "platform". After doping, the Fermi surface moves to the vicinity of the impurity energy level. In fact, the phenomena described in these five arxiv papers are so common that any system with a band gap can regulate doping so that flat impurity levels appear between bands, which has nothing to do with superconductivity.

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