As a crystal defect, the twin boundary has an important influence on the properties of superconducting materials and technical applications such as superconducting transition width and critical current. In many traditional superconductors, the superconducting transition temperature near the twin boundaries will increase slightly. Due to the short coherence length and strong anisotropy, the defects have a great influence on the superconducting properties of high-temperature superconductors. For example, YBCO twin boundaries can pin magnetic fluxes, thereby increasing the critical current. For iron-based superconducting materials, recent studies have found that the same material, such as Ba (Fe1-xCox) 2As2, has twin conflicting effects on superconductivity.
The spatial resolution of SQUID and other magnetic detection imaging technologies is generally in the range of a few hundred nanometers, while flux pinning may only occur at a scale of a few nanometers (close to the coherence length). Therefore, it is very difficult to determine from the existing magnetic imaging technology that a magnetic flux is pinned at or near the twin boundary. Scanning tunneling microscope / spectroscopy technology can simultaneously image twin boundaries and magnetic flux on the scale of coherent length. It can study the effect of twin boundaries on superconductivity on the basis of improving the resolution by 100 times.
In the past two years, the researcher Ma Xucun of the Institute of Physics of the Chinese Academy of Sciences / Beijing National Laboratory for Condensed Matter Physics (Preparation) Surface Physics and Academician Xue Qikun of the Department of Physics of Tsinghua University had molecular beam epitaxial growth and superconductivity of β-FeSe superconducting thin films Research has carried out in-depth research [Phys. Rev. B 84, 020503 (2011); Science 332, 1410 (2011)]. Recently, they collaborated with Professor Jennifer E. Hoffman of Harvard University to conduct a detailed in-situ study on superconductivity near twin boundaries in FeSe superconducting thin films using low temperature scanning tunneling microscope / spectroscopy.
They found that (1) by introducing Se impurities, "dumbbell" -like defects (μ and ν in Fig. 1) generated by Se replacing Fe atoms on the surface of FeSe were observed, and these defects were on a larger scale (~ 4.4 nm ) Breaks the crystal's quadruple symmetry to form an electronic dimer (yellow dotted line). By studying the different orientations of these electronic dimers, the twin boundaries in FeSe superconducting thin films were determined. (2) As approaching the twin boundary, the superconducting energy gap gradually decreases, and the superconducting coherent peak gradually weakens (Figure 2 and Figure 3). The superconducting energy gap (1.6meV) at the twin boundary is reduced by 25% compared to the energy gap (2.2meV) in the region without twin boundary, which proves that the twin boundary inhibits the FeSe film within the superconducting coherence length scale Superconductivity. (3) The magnetic flux is pinned preferentially at the twin boundary (Figure 4). The above results indicate that the twin boundary structure in the FeSe thin film weakens the superconductivity locally.
Considering that the STM morphology always shows that the twin boundary region is always higher than the surrounding FeSe thin film, and refer to the research on the structure and superconducting characteristics of single-crystal FeSe material under high pressure (such as pressure will cause hse to decrease and spin fluctuation to increase And Tc, etc.), the researchers speculate that there is a local increase in the height (hse) of Se relative to the Fe plane in the FeSe cell at the twin boundary, which will distort the structure of the FeSe4 tetrahedron and weaken the electron pair (π, π ) Spin fluctuations. This is the main possible cause of the local weakening of the superconducting properties at the twin boundaries.
These results are important for understanding the role of chalcogen / nitrogen group elements in iron-based superconducting compounds in the formation of Cooper.
The results have been published in Physical Review Letters (Phys. Rev. Lett. 109, 137004). This work was supported by funding from the National Natural Science Foundation and the Ministry of Science and Technology's major research program.
Figure 1: (ac) STM morphology of a β-FeSe superconducting thin film epitaxially grown on a graphene substrate. Excess Se atoms induce "dumbbell" -like defects and unidirectional electronic dimer structure. (d and e) Schematic diagram of the structure of β-FeSe and twin boundaries.
Figure 2: (ab) STM morphology near the twin boundaries. (c) Normalized dI / dV spectrum near the twin boundaries. (de) Differential conductance spectrum at zero bias (d) and corresponding coherent peak position energy (e).
Figure 3: The relationship between superconducting energy gap (Δ) and zero-bias piezoelectric conductance (ZBC) as a function of the distance between twin boundaries.
Figure 4: (ab) STM topography (a) and ZBC image (b) in the same area. (c) Schematic diagram of the twin boundaries and the position of the magnetic flux, indicating that the magnetic flux is mostly pinned to the twin boundaries.
New Grip is those grips new arrival or design by us,such as our original design Hummingbird Tattoo Grips.
Grips can be made of materials like stainless steel, plastic, aluminium, silicon, etc. Tattoo grips are used in together with
tube stems to form the grip that you hold a Tattoo Machine with. Stainless Steel Tattoo Grips require an autoclave to
properly sterilize. A barrier method to keep the tattoo grip clean like a tattoo machine bag can be used, however, it
is still necessary to properly sterilize all grips & tubes and needles via an autoclave if the intention is to reuse these products.
Silica Gel Tattoo Grips,Disposable Tattoo Cartridge Grip,Silica Gel Disposable Tattoo Grip,Silica Gel Disposable Grip
Amztatto Supply Co., Ltd. , https://www.amztatto.com