The correlation between superconductivity and a disordered structure is an interesting and challenging topic in condensed matter physics.Although scientists discovered amorphous superconductors as early as 1954，their superconducting mechanism has remained mysterious due to their complex chemical disorder，and limited investigative experimental techniques under extreme conditions.Recently，new work from a research team led by Dr. Wenge Yang of HPSTAR（Center for High Pressure Science &Technology Advanced Research）in collaboration with Prof. Ming Xu of Huazhong University of Science and Technology，and Prof. Matthias Wuttig of RWTH Aachen University found that density is closely related to superconductivity in amorphous solids.Detailed results are published in the recent issue of Physics Review Letters.
Under ambient conditions，the atoms in amorphous materials have a disordered arrangement where the electrons are severely localized，resulting in high electrical resistance in amorphous solids.However，many weakly disordered systems，including metallic glasses and high-entropy alloys，can also exhibit superconductivity.Disordering can even enhance the superconductivity of some amorphous systems.However，when the electronic localization caused by disorder reaches a critical level，the opposite effect-superconductivity-insulation transition will occur.From a structural perspective，it is difficult to accurately quantify the disorder in amorphous solids because they cannot be characterized as effectively as crystals，making the origin of their superconductivity uncertain.
“High pressure is a clean and efficient tool for tuning the physical properties of materials. So we used high pressure to change the atomic disorder of an amorphous solid to explore variations in its electrical localization further，”said Dr. Kai Zhang，the first author of the study.
A systematic high-pressure experimental and simulations study of amorphous Sb2Se3 was conducted to explore the pressure effect on its atomic arrangement and electron localization.Amorphous Sb2Se3 was chosen for its relatively stable disordered structure.Furthermore，its crystalline state exhibits a wealth of electronic behaviors such as strong spin-orbit coupling，topological insulation，and pressure-induced superconductivity.
By compressing to 240000 times the normal atmospheric pressure，the amorphous semiconductor Sb2Se3 exhibited the same superconductivity as the crystallized Sb2Se3.Moreover，in situ high-pressure high-energy X-ray diffraction shows that amorphous Sb2Se3 has a density crossover from a low-density to high-density state at the same pressure as the sample becomes superconducting.
With further compression，high-density amorphous Sb2Se3 crystallized at about 500000 times the normal atmospheric pressure，with a noticeable enhancement in superconductivity.Interestingly，superconductivity has a close correlation with the density change during the decompression process.
Additional theoretical calculations show that the intermediate high-density amorphous phase is the key to superconductivity occurrence in amorphous Sb2Se3.The high-density amorphous phase gave birth to ordered local structural units for the initial superconducting behavior.
“Actually，the high-density state is dominated by a unique“metavalent’chemical bond，which lies in between the low-pressure covalent bond and the high-pressure metal bond，unlike the low-voltage amorphous semiconductor phase and the high-pressure crystalline metal phase，”explained Dr. Yang Wenge.”Interestingly，the metavalent bond has been successfully applied in fields such as phase change materials or thermoelectric materials.“
“Our study provides a deep understanding of amorphous superconductors' atomic structure and electronic behavior，and amorphous phase change materials more generally. Exploring new materials such as thermoelectric materials stimulates broader research interest，”added Dr. Kai Zhang.
Caption: Density dependence of superconductivity at high pressure.
超導電性與無序結構的相關性一直是凝聚態物理領域一個有趣的和具有挑戰性的難題。雖然早在1954年科學家們就發現了非晶超導體，但由於非晶超導體中複雜的拓撲和化學無序性，以及極端條件下實驗科技的局限性使得非晶體中的超導機制一直是一個未解之謎。近日，北京高壓科學研究中心的楊文革研究員與華中科技大學的徐明教授，以及德國阿亨工業大學的Matthias Wuttig教授合作的研究團隊發現非晶態的密度和超導性具有緊密的聯系。相關結果以“Superconducting phase induced by a local structure transition in amorphous Sb2Se3 under high pressure”為題發表於近期的《物理評論快報》上。
以上內容來源於【北京高壓科學研究中心】官網：http://hpstar.ac.cn/contents/27/12346.html
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