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A very important property for a superconductor is that it can carry a non-dissipative superconducting current, which enables it to produce a huge magnetic field when transforming the superconductor into a magnet. This property can be applied for medical treatment, controlled nuclear fusion, high energy accelerator, new generation of maglev transport, etc. For a superconductor to carry the non-dissipative supercurrent, a limit, namely the line of irreversibility Hirr(T), is very crucial. This phase line effectively separates the phase diagram into zero and finite resistive dissipation. Usually, if a superconductor can support a higher non-dissipative supercurrent with a higher irreversibility magnetic field, it will have a better perspective for applications.
A superconductor goes into a superconducting state less than the transition temperature Tc, so a superconductor with more Tc has better potential applications. Liquid nitrogen is an easy to manufacture and inexpensive cryogen, with a boiling temperature of about 77.3 K. It is essential for applications to find superconductors with Tc beyond the boiling temperature of liquid nitrogen and a magnetic field of high irreversibility. In the family of cuprates, certain compounds of the compound based on Y[YBa[YBa[YBa[YBa2Cu3O7–δ (Y-123), TcK90K]Bi-base[Bi[Bi[Bi[Bi2Sr2California2Cu3O10+δ (Bi-2223), TcK110K]Mercury based[HgBa[HgBa[HgBa[HgBa2California3Cu4O10+δ (Hg-1234), Tc124 K €], and based on Tl[Tl[Tl[Tl[Tl2Ba2California2Cu3O10+δ (Tl-2223), Tc125]The systems display superconducting transition temperatures above 77K. However, for systems based on Hg and Tl, the toxic elements Hg and Tl strongly constrain the high-power applications of these materials. The non-toxic bi-based system also has a transition temperature greater than 100 K, but the highly stratified structure and the large anisotropy do not allow a high field of irreversibility at the temperature of liquid nitrogen: the Irreversibility field and superconducting current density decrease rapidly with moderate temperature region temperature. The YBa Y-based2Cu3O7–δ (YBCO), which is nontoxic and has a high field of irreversibility, is considered a promising material for applications. But it is extremely difficult to produce a long superconducting wire for the short length consistent, it can not realize large-scale applications up to now.
The group of Professor Hai-Hu Wen from the Department of Physics of Nanjing University has succeeded in synthesizing the nontoxic superconductor to cuprate (Cu, C) Ba2California3Cu4O11+re with Tc= 116 K under high pressure and high temperature. The systematic measurements of resistivity and magnetization show that it has the most irreversible magnetic field in the temperature region of liquid nitrogen. This work was recently published in Scientific advances 4, eaau0192 (2018) September 28, 2018.
Figure 1 shows the temperature-dependent resistivity of Sample 1 under different magnetic fields. If a resistivity criterion of 1% ρnot(Tc) is chosen, as indicated by the blue horizontal dotted line, the determined irreversibility field is from 15 T to about 82K. In fact, even higher values of irreversibility fields are found in another sample. If the weak links between polycrystalline samples are improved, the line of irreversibility can be even higher.
Fig 1. Dependence of resistivity and magnetization of sample 1 as a function of temperature. (A)
Dependence of resistivity versus temperature under different magnetic fields from 0 to 15 T. The inset indicates the temperature dependence of the magnetic susceptibility measured in the ZFC and FC modes under a magnetic field of 10 Oe. (B) The same data in (A) in the semilogarithmic scale. Blue horizontal dotted line represents the 1% resistivity criterion ρnot(Tc), which is used to determine the line of irreversibility.
Figure 2 shows the comparison of the irreversibility lines of our samples and other cuprate systems (including polycrystalline samples, film / monocrystal with H // c). From the data, we can see that the irreversibility field of (Cu, C) Ba2California3Cu4O11+re is the highest in the temperature region between 77 K and 116 K. We use the highlighted area to indicate the region with finite supercurrent (or zero / low resistive dissipation) of our sample versus YBCO. It can be seen that there is a large area beyond YBCO's irreversibility line, where the samples may have a non-dissipative supercurrent, which offers great potential for applications exceeding liquid nitrogen temperatures. This can stimulate the search for cuprate-based superconductors and eventually lead to large losses. large scale applications.
Fig 2. Irreversibility lines of different cuprate systems.
Irreversibility lines for (Cu, C) -1234 (our work, samples 1 and 2), YBCO 1 and YBCO 2 (single crystals, H || c axis), Bi-2223 (thin layer, blue triangles down), Bi-2223 (single crystal, cyan diamond) and (T1, Pb) -1223 (pink triangles). The highlighted area indicates the region for zero dissipation above the YBCO limit. The black dotted line shows the evolution of YBCO's line of irreversibility with Tc = 91 K.
It should be emphasized that the current samples were manufactured by high pressure synthesis. The present results show very good intrinsic properties for the application of the non-toxic material (Cu, C) Ba2California3Cu4O11+re and related systems. It is highly desirable to try new methods with less pressure or thin layer deposition to make the superconducting wire / tape from this promising material.
This work is independently completed by the group of Professor Hai-Hu Wen, the doctoral student Yue Zhang is the first author of the article, Professor Hai-Hu Wen and Xiyu Zhu are the corresponding authors.
Link to the article: http: //advances.sciencemag.org/content/advances/4/9/eaau0192.full.pdf
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