is like the freely floating mountain in the movie " Avatar ", can people realize superconducting at room temperature one day in the future? This is not a "day talk", but a scientific research topic that scientists are exploring and may be realized in the future.
magnetic levitation train, nuclear magnetic resonance meter , superconducting cable , superconducting transformer... These are the applications of the superconductivity of materials in life.
1986, a laboratory in Zurich, Switzerland, IBM was established to dopant other substances in copper-based ceramic insulators to achieve superconductivity for the first time, which is regarded as a "landmark research breakthrough in superconductivity." Then in 2011, iron-based superconducting was first discovered by Japanese scientists.
In 2019, Stanford University realized superconducting in nickel-based oxides.
Scientists are constantly studying the mechanisms of existing superconducting materials, and are also trying to expand these mechanisms into the development of novel materials.
Recently, the team of Dr. Zhou Kejin, chief beam wire scientist of Diamond Light Source in the UK, has made new progress in the field of superconducting materials [1]. The team discovered magnetic excitation in an infinite layer nickel-based oxide superconductor and measured charge density waves, laying a good foundation for understanding the origin of nickel-based superconductors and the superconducting mechanism.
(Source: Pixabay)
Select RIXS as a research technology
X ray scattering technology is a powerful experimental method to detect the properties of materials. Dr. Zhou Kejin led the research team to select resonant inelastic X-ray scattering with an incident energy of 0.4-20keV and an energy transfer range of 0.01-10eV. Scattering) technology.
Figure | X-ray scattering technology (Source: Zhou Kejin)
"This is more targeted for studying the low-energy collective excitation properties of advanced materials in solid materials, especially nano-thick film states." Zhou Kejin said.
Figure | Diamond Light Source (Source: Zhou Kejin) RIXS experimental equipment for
Diamond Light Source can purify and focus high-energy X-rays to form a tiny elliptical high-intensity, high-purity X-ray spot (30μm in horizontal direction and 2μm in vertical direction). The function of high-purity spots is to inject some electrons near the innermost atomic nucleus of the solid material into a vacuum. Eventually, other electrons fill the hole level and emit X-ray fluorescence.
Figure | RIXS scattering process (Source: Zhou Kejin)
This instrument can distinguish energy and momentum from the scattered X-rays. By the difference in energy and momentum of the outgoing light and incident light, the microscopic electronic state information of the material can be reflected, and this information is related to the macroscopic properties of the material. Zhou Kejin explained: "Insulation, conductivity and superconductivity are closely related. It is precisely this principle that we use to study the properties of the target material."
33 Measurement of the charge density wave in infinite layer NdNiO2 nickel-based superconducting materials
In materials science, people have been committed to reproducing the superconductivity of materials. To this end, Zhou Kejin cooperated with University of Electronic Science and Technology to successfully observe the charge density wave in the infinite layer nickelate (NdNiO2) film with RIXS, and reproduced the ordered electronic states widely present in copper-based superconductors in nickel-based superconductors.
Recently, a related paper was published on Nature Materials Nature Materials Nature Materials [2].
(Source: Nature Materials)
In the initial research stage of the research, the material acquisition, research difficulty, and measurement methods make the research "hard".
Specifically, the infinite layer NdNiO2 nickel-based film material is only 10 nanometers thick and is on the atomic order, so it is difficult to obtain. Moreover, there are no more than ten research groups in the world that can truly generate high-quality nickel-based thin film superconducting oxides. In addition, the experimental methods for determining the charge density wave of this material are also very limited.
To solve the problem of material acquisition, the team cooperated with the University of Electronic Science and Technology of Sichuan, China to obtain the samples needed for the experiment. From the technical aspects, the penetration depth of the RIXS spectral is about a few dozen nanometers, and a weak electronic signal can be observed just right, which is exactly matched with the material thickness.
Figure | Charge density waves in parent NNO2 (Source: Nature Materials)
Figure | Charge density waves in NdNiO2 and superconducting Nd0.8Sr0.2NiO2 (Source: Nature Materials)
In this study, Zhou Kejin's team made detailed decomposition of the mechanism of charge density waves, and found that the electrons in the nickel oxygen layer are related to each other, which will debug the charge density waves. As the interaction between electrons between two elements weakens, the charge density wave also tends to weaken.
"We observed a very strong charge density wave in the parent infinite layer nickelate. When the doping amount of strontium element (Sr) is 20%, the material becomes a superconductor and the charge density wave disappears." Zhou Kejin said.
They also found that some longer and ordered charge density waves and superconductivity can form a competitive mechanism. Simply put, there is no superconducting with charge density waves, and the charge density waves with superconducting will weaken. This appearance of
reminded Zhou Kejin and his team that the competition between superconductivity and charge density waves in copper-based oxide superconductors is widely present.
He further said: "Nickelates have multi-electron orbital characteristics different from copper acid . Research on them can provide a good example for a deep understanding of the basic mechanism of high-temperature superconducting ."
Explore the magnetic excitation properties of infinite layer nickel-based superconductors
Are the electron behavior and spin interactions in nickel-based superconductors really exactly similar to copper-based oxides? Is the magnetic exchange strength of the infinite layer nickel-based oxide one fifth or one tenth of that of the copper-based, or is it comparable?
To explore the magnetic excitation properties of infinite layer nickel-based superconductors, Zhou Kejin's team worked with Stanford University to redefine its fuzzy concept through actual measurements.
(Source: Science)
Recently, a related paper was published on ScienceScience[3].
Figure | Magnetic excitation under RIXS spectral line (Source: Science)
Infinite layer nickel-based oxide superconductor As the main material studied in the paper, it has a structure similar to copper-based oxide. The researchers irradiated the nickel-based compound with high strength, high purity X-rays and hit the core energy level electrons onto the surface conduction band. At this time, the other occupied electrons will jump down. In this process, the magnetic excitation of the material is derived.
Figure | Changes in magnetic excitation energy and momentum in NdNiO2 observed by RIXS (Source: Science)
Then, the experiments determined the relationship between RIXS intensity and NdNiO2 momentum and energy. The peak position of the magnetic excitation spectrum scattered by RIXS is in a dispersive state. As momentum continues to increase, energy slowly deflects.
Figure | Fitting of dispersion and linear spin waves in NdNiO2 (Source: Science)
Zhou Kejin said: "Interestingly, although nickel-based superconductors have not been proven to hold long-range ordered antiferromagnetic states, we found that there is a strong antiferromagnetic excitation in the parent material." After finding the dispersion relationship, the team fitted the data of this dispersion relationship, and then extracted the interaction intensity of the magnet. The fitting results of
show that the nearest electron spin interaction intensity is close to 60 HOU electron volts . This value is about half the value of copper-based superconducting oxide.
It is worth noting that the dispersion relationship of the nickel-based group is almost the same as that of the copper-based group, and the magnetic excitation spectrum has a clear peak shape, which shows that the correlation between electrons and electrons is very strong and very similar to that of copper-based superconductors.
Figure | RIXS spectroscopy of superconducting Nd1-xSrxNiO2 (Source: Science)
Finally, the research team also observed some of the evolved behaviors of magnetic excitation in NdNiO2. When strontium is doped, NdNiO2 will be converted into a superconductor, and a slight change will occur after magnetic excitation.
Acquisition of any scientific research results is not achieved overnight. Whether it is discovering magnetic excitation in nickel-based superconducting materials or measuring charge density waves, people are one step closer to exploring the superconductivity of advanced materials. From alloy superconductors to current copper-based oxide superconductors, to nickel-based oxides, scientists are still looking for new superconducting materials and are working tirelessly to explore the new characteristics of superconductors.
Reference:
1. https://www.diamond.ac.uk/Instruments/Magnetic-Materials/I21.html
2. Charles C.Tam, Jaewon Choi, Xiang Ding, Stefano Agrestini, Abhishek Nag, Mei Wu, Bing Huang, Huiqian Luo, Peng Gao, Mirian García-Fernández , Liang Qiao and Ke-Jin Zhou , Nat. Mater. 21, 1116-1120 (2022). Charge density waves in infinite-layer NdNiO2nickelates, https://www.nature.com/articles/s41563-022-01330-1.
3.H.Lu, M.Rossi, A.Nag, M.Osada, D.F.Li, K.Lee, B.Y.Wang, M.Garcia-Fernandez, S.Agrestini, Z.X.Shen, E.M.Been, B.Moritz, T.P.Devereaux, J.Zaanen, H.Y.Hwang, Ke-Jin Zhou, W.S.Lee, Science. 373, 213-216 (2021), Magnetic excitations in infinite-layernickelates, https://www.science.org/doi/10.1126/science.abd7726
