1Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China 2School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China 3School of Physical Science and Technology, Guangxi University, Nanning 530004, China 4Songshan Lake Materials Laboratory, Dongguan 523808, China 5CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
Abstract：We report a hydrothermal route to remove interstitial excess Fe in non-superconducting iron chalcogenide Fe$_{1+\delta}$Se$_{1-x}$Te$_{x}$ single crystals. The extra-Fe-free ($\delta \sim 0$) FeSe$_{0.2}$Te$_{0.8}$ single crystal thus obtained shows bulk superconductivity at $T_{\rm c} \sim 13.8$ K, which is about 2 K higher than the FeSe$_{0.2}$Te$_{0.8}$ sample obtained by usual post-annealing process. The upper critical field $\mu_{0}H_{\rm c2}$ is estimated to be $\sim$ $42.5$ T, similar to the annealed FeSe$_{0.2}$Te$_{0.8}$. It is surprising to find that the hydrothermal FeSe$_{0.2}$Te$_{0.8}$ exhibits a remarkably small isothermal magnetization hysteresis loop at $T = 3$ K. This yields an extremely low critical current density $J_{\rm c} \sim 1.1\times 10^{2}$ A$\cdot$cm$^{-2}$ (over 100 times smaller than the annealed FeSe$_{0.2}$Te$_{0.8}$) and indicates more free vortices in the hydrothermal FeSe$_{0.2}$Te$_{0.8}$.
Fang M H, Pham H M, Qian B, Liu T J, Vehstedt E K, Liu Y, Spinu L, and Mao Z Q 2008 Phys. Rev. B78 224503
[2]
Yin J X, Wu Z, Wang J H, Ye Z Y, Gong J, Hou X Y, Shan L, Li A, Liang X J, Wu X X, Li J, Ting C S, Wang Z Q, Hu J P, Hor P H, Ding H, and Pan S H 2015 Nat. Phys.11 543
[3]
Wang D F, Kong L Y, Fan P, Chen H, Zhu S Y, Liu W, Cao L, Sun Y J, Du S X, Schneeloch J, Zhong R, Gu G, Fu L, Ding H, and Gao H J 2018 Science362 333
[4]
Zhang P, Yaji K, Hashimoto T, Ota Y, Kondo T, Okazaki K, Wang Z, Wen J, Gu G D, Ding H, and Shin S 2018 Science360 182
[5]
Zhao H, Li H, Dong L, Xu B, Schneeloch J, Zhong R, Fang M, Gu G, Harter J, Wilson S D, Wang Z, and Zeljkovic I 2021 Nat. Phys.17 903
Si W D, Han S J, Shi X Y, Ehrlich S N, Jaroszynski J, Goyal A, and Li Q 2013 Nat. Commun.4 1347
[8]
Liu X, Wei S, Shi Y, Liu F, Zhou C, Li Q, Li Y, Liu L, Shi Z, Ren L, Xu Y, Duan P, Yang Z, Ge J, Qi Y, Song Y, Liu H, Zhang Z, and Qin J 2022 Supercond. Sci. Technol.35 10LT01
Bendele M, Babkevich P, Katrych S, Gvasaliya S N, Pomjakushina E, Conder K, Roessli B, Boothroyd A T, Khasanov R, and Keller H 2010 Phys. Rev. B82 212504
[11]
Hu H F, Zuo J M, Wen J S, Xu Z J, Lin Z W, Li Q, Gu G D, Park W K, and Greene L H 2011 New J. Phys.13 053031
[12]
Okazaki H, Watanabe T, Yamaguchi T, Kawasaki Y, Deguchi K, Demura S, Ozaki T, Denholme S J, Mizuguchi Y, Takeya H, and Takano Y 2012 J. Phys. Soc. Jpn.81 113707
Eguchi R, Senda M, Uesugi E, Goto H, Fujiwara A, Imai Y, Kimura S, Noji T, Koike Y, and Kubozono Y 2020 Mater. Res. Express7 036001
[16]
Sun Y, Pan Y, Zhou N, Xing X, Shi Z, Wang J, Zhu Z, Sugimoto A, Ekino T, Tamegai T, and Kitano H 2021 Phys. Rev. B103 224506
[17]
Bao W, Qiu Y, Huang Q, Green M A, Zajdel P, Fitzsimmons M R, Zhernenkov M, Chang S, Fang M, Qian B, Vehstedt E K, Yang J, Pham H M, Spinu L, and Mao Z Q 2009 Phys. Rev. Lett.102 247001
[18]
Liu T J, Ke X, Qian B, Hu J, Fobes D, Vehstedt E K, Pham H, Yang J H, Fang M H, Spinu L, Schiffer P, Liu Y, and Mao Z Q 2009 Phys. Rev. B80 174509
Otsuka T, Hagisawa S, Koshika Y, Adachi S, Usui T, Sasaki N, Sasaki S, Yamaguchi S, Nakanishi Y, Yoshizawa M, Kimura S, and Watanabe T 2019 Phys. Rev. B99 184505
[28]
Liu T J, Hu J, Qian B, Fobes D, Mao Z Q, Bao W, Reehuis M, Kimber S A J, Prokeš K, Matas S, Argyriou D N, Hiess A, Rotaru A, Pham H, Spinu L, Qiu Y, Thampy V, Savici A T, Rodriguez J A, and Broholm C 2010 Nat. Mater.9 718
Liu L, Mikami T, Takahashi M, Ishida S, Kakeshita T, Okazaki K, Fujimori A, and Uchida S 2015 Phys. Rev. B91 134502
[32]
Yuan D N, Huang Y L, Ni S L, Zhou H X, Mao Y Y, Hu W, Yuan J, Jin K, Zhang G M, Dong X L, and Zhou F 2016 Chin. Phys. B25 077404
[33]
Ni S L, Hu W, Shen P P, Wei Z G, Liu S B, Li D, Yuan J, Yu L, Jin K, Zhou F, Dong X L, and Zhao Z X 2019 Chin. Phys. B28 127401
[34]
Liu Q, Chen C, Zhang T, Peng R, Yan Y J, Wen C H P, Lou X, Huang Y L, Tian J P, Dong X L, Wang G W, Bao W C, Wang Q H, Yin Z P, Zhao Z X, and Feng D L 2018 Phys. Rev. X8 041056
2023, Vol. 40 
