Can nano-sized stripes be an important reason for superconductivity?

A team in Germany has discovered the existence of special structures in the form of nanometer-sized stripes (nanostripe) in a high-temperature superconducting compound made of SmBaCuO ceramic compounds. Many physicists believe that this structure plays an important role in creating superconductivity, while many other physicists disagree with this hypothesis.

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This new result not only caused lively debates but also sheds light on many issues related to the origin of high-temperature superconductivity, which remains one of the greatest mysteries of physics. in the past 2 decades.

Most current high-temperature ceramic superconductors often contain parallel surfaces of copper oxide (CuO) with other elements sandwiched between these layers. Copper atoms are located on a square grid and the charge is transported by holes located in the oxygen position. Previous X-ray scattering measurements on YBaCuO superconducting ceramic materials have shown that the spectrum containing characteristic diffusion lines is thought to be the formation of stripes in the copper oxide surfaces. Many physicists believe that these stripes will create transport channels for superconducting currents.

However, in 2004, researchers in Germany discovered that these properties originated from defects in oxygen. Simultaneously with these results, an independent US team also observed nanoscale diodes, and hypothesized to be superstructures like those observed by the German team. These results mean that charge stripes may not play a role in the superconducting transport of high-temperature superconductors.

Figure 1. AFM image (a) and STM (b) of single crystals Sm123.
Both images show periodic stripes with a period of about 50 nm
(According to Supercond. Sci. Technol. 20 681).

Recently, Michaeal Koblischka and her colleagues at Saarland University (Saarbruecken, Germany) observed structures of nanoscale stripes in SmBaCuO compound . The observation image on the tunneling microscope shows that these stripes are almost parallel to each other at intervals of up to several inches long, and occasionally create ripples. The researchers suggest that these structures may act as "pinning sites" by circulating at very small sizes (only between 10 and 60 nm). These are ideal sizes of brakes to create high critical current density even at temperatures around 77 K.

Koblischka's group also observed these stripes in SmBaCuO crystal monoliths fabricated by top-speed techniques and in directional melting patterns. Detailed observations on AFM and STM show that these nanotubes are formed by separate sequences of nanocrystals (nanocluster) from the unit cells of the rich phase Sm (Sm ₁ + xBa ₂ -xCu ₃ Oy ).

Figure 2. The nanostripe observed in directional molten samples
(According to Supercond. Sci. Technol. 20 681).

"The phase transition temperature is as high as 93.5 K and the critical current density is as high as 38000 A / cm2 (at 77 K and 2 T magnetic fields) making this material extremely useful for block applications (eg as the levitation application (suspended phenomena) " - Koblischka said -" Although the cause of this superconducting improvement has not been elucidated, the appearance of nano stripes can will be the key to explaining ".

Physicists also predict that controlling the braking centers along the body volume can help to improve the critical current density even more, especially in high magnetic fields.See details of the results just published in Superconductor Science and Technology 20 (2007) 681 .

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