In an article published in Physical Review express on may20,2022, the research team of Jilin University introduced a new high-temperature superconductor synthesized by it - cage calcium hydride (CAH ₆) It can be seen that as one of the best high-temperature super hydrides (and also the only cage hydrides outside the rare earth and actinide hydrides family), it has superconductivity at 215 K and 172 GPA (1.72 mbar) high pressure.
(picture from: Jilin University / wanghongbo)
Physics World It is reported that after ten years of theorizing, Chinese scientists have finally synthesized this new type of high-temperature superhydrogen superconductor.
As for superconductivity, it refers to the ability of a material to conduct electricity without any resistance. This phenomenon can be observed in many materials when cooled to the superconducting transition temperature (TC).
In Bardeen Cooper Schrieffer's' conventional 'superconducting theory, it specifically refers to that electrons overcome the electric repulsion between each other, form the so-called Cooper pairs, and then the super current can pass through the material unimpeded.
Since superconductivity was first observed in TC solid mercury below 4.2 K in 1911, researchers have not given up looking for various room temperature superconductors.
If applied at room temperature, such superconducting materials will greatly improve the efficiency of generators and transmission lines.
At the same time, common superconducting applications can also benefit from this. For example, the manufacturing of superconducting magnets in particle accelerators will be easier and more affordable.
Research diagram - 1: laser heating / 190 GPA structure
Now, the State Key Laboratory of superhard materials under the school of physics of Jilin University( http://nlshm-lab.jlu.edu.cn/index.htm ) A research team of has successfully synthesized a new type of superhydrogen containing alkaline earth metals (rather than rare earth metals / actinides).
The researchers claim that this discovery has opened a new door to the study of a class of superconductors that has not yet been explored. In fact, as early as ten years ago, some theories predicted that CAH ₆ was a unique cage superconductor.
The problem is that due to the high reactivity of calcium and hydrogen, the actual material synthesis of CAH ₆ has been quite difficult. If we try to combine the two elements only in a low-pressure environment, the hydrogen content of the hydride is often too low to be pleasant.
Figure 2: optical micrograph / resistance measurement of laser heated samples at 170 GPA
In order to overcome this difficulty, researchers try to use aminoborane (BH ₃ NH ₃) as hydrogen source, and then synthesize CAH ₆ through direct reaction between Ca and H ₆ under high temperature and high pressure.
Associate professor wanghongbo explained that "we used a special sample loading method and synthesized the material in the diamond anvil at a temperature close to 200 GPa and 2000 K".
Then they carefully installed the microelectrode on the tip of the anvil for subsequent conductivity measurement.
Figure 3: temperature dependence of resistance in magnetic field environment
The sharp drop in resistance is very similar to other superconducting transition studies conducted by the team under high voltage, and they have been repeated successfully for many times.
Thanks to the latest research work, it is expected to promote people's in-depth understanding of superconductivity and even give birth to novel ternary calcium based super hydrides.
At present, they are busy exploring a wider range of superconducting materials based on their own and other team's calculations, and firmly believe that more super hydrides with higher TC values can be found.
Details of this study have been published in the physical review letters published on may20,2022( https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.167001 ) ) Up.
The original title was "high temperature superconducting phase in clausrate calcium hydrate CAH ₆ up to 215 K at a pressure of 172 GPA".