Application-oriented syntheses of FeSe-based superconductor films and studies of their critical parameters
Final Report Abstract
This project aimed at investigating fundamental yet application-relevant properties in chalcogenide Fe-based superconductors by synthesizing and investigating them in the form of high-quality thin films of two different crystal structures and elucidating the underlying mechanisms of superconductivity. The chalcogenide FeSe-based superconductors belong to the Fe-based superconductors (FBS), which were discovered in 2006/08 and attracted strong scientific interest due to their high transition temperatures of up to 55 K and very high upper critical magnetic fields well above 50 T, which render them promising for high magnetic field applications. The main three crystal structure classes of FBS with the highest potential for applications and most widely investigated are the so-called 11 [i.e. Fe(Se,Te)], differently doped 122 [mostly BaFe2As2], and 1111 [LnFeAs(O,X), Ln lanthanoide, X=H,F] structures. (Li,Fe)OHFeSe, discovered in 2014 by Lu et al. can be regarded in two ways: it resembles the 1111 crystal structure if the hydroxyl group is regarded as single entity and therefore may be seen as the chalcogenide equivalent of the pnictide 1111 compounds. On the other hand, it may be regarded as FeSe with large spacer layer (Li,Fe)OH, i.e. expanded c-axis lattice parameter. It is therefore a link between bulk samples of the simplest FBS structure FeSe with critical temperatures Tc ~ 10 K and single-unit-cell films of FeSe on SrTiO3 with a superconducting gap opening above 65 K. With the latter, (Li,Fe)OHFeSe shares a similar electronic structure consisting of electron pockets near the Brillouin zone corners and therefore similar electronic properties, namely highly 2D, electron-dominated multi-band superconductivity with strong 2D spin fluctuations. (Li,Fe)OHFeSe films are grown by matrix-assisted hydrothermal epitaxy (MHE) and show single crystalline properties. FeSe and its Te-doped version Fe(Se,Te) with higher Tc (~18 K) has the most simple crystal structure of all FBS. Yet, understanding this system and synthesizing samples of high quality is not as straightforward as one might expect from the structural simplicity. This is mainly due to the strong dependence of the superconducting properties on the strain state (i.e. the lattice constants), the stoichiometry Se-Te, and possible excess iron. Regarding the Se-Te stoichiometry, thin film growth offers the possibility to prepare samples with low Te content which are inaccessible as single crystals yet show the highest Tc values. The aim of this project was to cross-investigate different deposition and doping methods on films in the two material classes: Mn doping in FeSe and Fe(Se,Te) as well as Te doping of (Li,Fe)OHFeSe, also in multilayer architectures. These doping studies were to be extended for both types of FeSe-based superconducting films with further dopants, such as Mg, Co, Ni, Cu, and Zn.
Publications
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Magnetic-Field-Induced Spin Nematicity in FeSe1 – x S x and FeSe1 – y Te y Superconductor Systems. Chinese Physics Letters, 38(8), 087401.
Liu, Shaobo; Yuan, Jie; Ma, Sheng; Lu, Zouyouwei; Zhang, Yuhang; Ma, Mingwei; Zhang, Hua; Jin, Kui; Yu, Li; Zhou, Fang; Dong, Xiaoli & Zhao, Zhongxian
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Unusual Normal and Superconducting State Properties Observed in Hydrothermal Fe1-δ Se Flakes. Chinese Physics Letters, 38(5), 057401.
Liu, Shaobo; Ma, Sheng; Wang, Zhaosheng; Hu, Wei; Li, Zian; Liang, Qimei; Wang, Hong; Zhang, Yuhang; Lu, Zouyouwei; Yuan, Jie; Jin, Kui; Li, Jian-Qi; Pi, Li; Yu, Li; Zhou, Fang; Dong, Xiaoli & Zhao, Zhongxian
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A disorder-sensitive emergent vortex phase identified in high-T c superconductor (Li,Fe)OHFeSe. Superconductor Science and Technology, 35(6), 064007.
Li, Dong; Shen, Peipei; Tian, Jinpeng; He, Ge; Ni, Shunli; Wang, Zhaosheng; Xi, Chuanying; Pi, Li; Zhang, Hua; Yuan, Jie; Jin, Kui; Talantsev, Evgeny F.; Yu, Li; Zhou, Fang; Hänisch, Jens; Dong, Xiaoli & Zhao, Zhongxian
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Quasi-Two-Dimensional Nature of High-T c Superconductivity in Iron-Based (Li,Fe)OHFeSe. Chinese Physics Letters, 39(12), 127402.
Li, Dong; Liu, Yue; Lu, Zouyouwei; Li, Peiling; Zhang, Yuhang; Ma, Sheng; Liu, Jiali; Lu, Jihu; Zhang, Hua; Liu, Guangtong; Zhou, Fang; Dong, Xiaoli & Zhao, Zhongxian
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Recent Developments in Fe- Based Superconductors – Towards Understanding Their Vortex Matter and Possible Applications, invited talk, MRS Spring Meeting, 24.05.22, online
J. Hänisch
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Effect of carbon doping on magnetic flux pinning and superconducting performance in FeSe0.5Te0.5 single crystals. Superconductor Science and Technology, 36(2), 025008.
Zhang, J.; Hänisch, Jens; Yang, X. S.; Zhao, K. & Zhao, Y.
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Hydrothermally Obtaining Superconductor Single Crystal of FeSe0.2Te0.8 without Interstitial Fe. Chinese Physics Letters, 40(6), 067402.
Ma, Sheng; Yan, Shanshan; Liu, Jiali; Wang, Yizhe; Zhang, Yuhang; Zhao, Zhen; Lu, Zouyouwei; Li, Dong; Liu, Yue; Lu, Jihu; Zhang, Hua; Yang, Haitao; Zhou, Fang; Li, Zian; Dong, Xiaoli & Zhao, Zhongxian
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Recent progress on epitaxial growth of Fe-based superconducting thin films. Superconductor Science and Technology, 36(6), 063001.
Iida, Kazumasa; Hänisch, Jens; Hata, Satoshi & Yamamoto, Akiyasu
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Vortex matter, anisotropy, and electrical transport in (Li,Fe)OHFeSe thin films, invited talk, MRM2023, Kyoto, Japan, 11.-16.12.2023
J. Hänisch, S. Tokatldidis et al.
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Critical current density in advanced superconductors. Progress in Materials Science, 155, 101492.
Ruiz, H.S.; Hänisch, J.; Polichetti, M.; Galluzzi, A.; Gozzelino, L.; Torsello, D.; Milošević-Govedarović, S.; Grbović-Novaković, J.; Dobrovolskiy, O.V.; Lang, W.; Grimaldi, G.; Crisan, A.; Badica, P.; Ionescu, A.M.; Cayado, P.; Willa, R.; Barbiellini, B.; Eley, S. & Badía–Majós, A.
