room-normal temperature superconductivity
Is room-normal temperature superconductivity a technological a technological revolution or an empty joy？
On July 22, 2023, a paper published on arXiv announced the discovery of a crystal structure called LK-99 that can superconduct at room temperature and normal atmospheric pressure. The news was like a bombshell thrown in the press and triggered a heated discussion among the public. At the same time, many scientific research institutions also responded quickly and tried to reproduce the paper. The huge potential of room-normal temperature superconductivity to reshape existing industries and lead economic and technological development is the source of its popularity, and people even call it the key that may open the next scientific and technological revolution.
Superconductivity applied to power systems can replace UHV transmission lines and eliminate about 15% of their total losses, contributing to energy security and green mountains. Superconductivity is applied to chip specialties, which can greatly reduce costs and improve operating speed, and guarantee precision instruments such as interferometers. The application of superconductivity in traffic can make the superconducting maglev train shine into reality, and the smooth flow of people and goods can highlight economic vitality. So is room-temperature superconductivity really coming?
Throughout the history of superconductivity, its breakthrough discoveries often set off a wave of academic research, and then gradually calm down until the next breakthrough. In 1911, the Dutch physicist Onnes used liquid helium to refrigerate and observed that mercury seemed to lose its resistance at 4.2 Kelvin (K), thus showing the phenomenon of superconductivity in front of the world. Inspired by this, a series of achievements such as lead superconducting at 7.2K and niobium superconducting at nearly 9K have been discovered. The research of superconductivity based on niobium has found materials such as niobium titanium alloy with 10K critical, niobium nitride with 16K critical and niobium trigermanium with 23K critical.
At this time, the academic community gradually realized that the main factor hindering the wide application of superconducting materials was the harsh temperature requirements, and the low temperature environment of 19K, that is, about -250℃, required the use of expensive liquid helium manufacturing. Therefore, research has focused on finding materials with higher critical superconducting temperatures. Even if room-normal temperature superconductivity is far away, if the critical temperature exceeds 77K, relatively cheap liquid nitrogen can be used to replace liquid helium refrigeration, thus significantly reducing the cost of superconducting applications. However, in the following ten years, there was no breakthrough in relevant research, and the craze for superconducting materials gradually subsided until 1986.
This year, the discovery of lanthanum-containing copper based materials superconducting at 30K ignited the enthusiasm of the academic community. Under the guidance of the new idea of copper based, the full attempt and exploration soon found that the critical temperature of superconductivity of mercury series copper based materials can reach the highest 134K, breaking through the goal of liquid nitrogen refrigeration. The next research boom was in the second decade of the new century, it was found that the critical temperature of superconductivity of hydrogen-based materials can be as high as nearly 200K under high pressure conditions of millions of atmospheric pressure, and the desire for room-normal temperature superconductivity seems to be a work in progress.
However, if you take apart a superconducting accelerator, it is highly likely that you will see neither copper nor hydrogen-based superconducting materials, but niobium titanium alloy, although the critical temperature is not outstanding, but the mechanical properties are relatively good and the process is simple. Considering the electrical and mechanical properties, manufacturing process, economy, etc., the high pressure that relies on diamond to produce a million times atmospheric pressure on the anvil or the complex high temperature process of copper-based superconducting materials make it difficult for them to enter thousands of households from the laboratory. So when a material, as LK-99 claims, is also room-temperature superconducting, simple to process, and cheap to make, it’s not hard to imagine that it’s going to get heated.
So, does the LK-99 really live up to its name? Academic opinion remains divided. Lawrence Berkeley National Laboratory in the United States has adopted computer simulation and found that the preparation method is theoretically feasible. Some professors are also confident because of the semi-suspension of the LK-99 in the demonstration video and the zero-resistance signal measured by the Southeast University team. However, the voices of doubt and opposition are also endless. The Princeton and University of Maryland teams believe that the impurity removal of LK-99 is not a superconductor. Research from Peking University’s Center for Quantum Materials Science also showed that it did not exhibit superconductivity.
On August 16, Natural Impurities published a paper stating that LK-99 is not a superconductor, explaining the reasons for its superconducting appearance while listing the evidence: (1) The decrease in the resistivity of the sample is due to the presence of cuprous sulfide impurities; (2) semi-suspension may result in ferromagnetism; (3) LK-99 with the elimination of impurities has a high resistivity. Indeed, if high-speed rail and maglev trains can obtain the support of room-normal temperature superconductivity technology, it will reach a new level in terms of operation speed and energy saving and consumption reduction. However, the exploration of room-normal temperature superconductivity should perhaps be as Xinhua said: patience, research is the greatest kindness to the new technology.
