Investigation of Iron Selenide Superconducting Thin Films Fabricated by Pulsed Laser Deposition

University of Wollongong Research Online University of Wollongong Thesis Collection 2017+ University of Wollongong Thesis Collections 2018 Investigation of Iron Selenide Superconducting Thin Films Fabricated by Pulsed Laser Deposition Wenbin Qiu University of Wollongong Follow this and additional works at: https://ro.uow.edu.au/theses1 University of Wollongong Copyright Warning You may print or download ONE copy of this document for the purpose of your own research or study. The University does not authorise you to copy, communicate or otherwise make available electronically to any other person any copyright material contained on this site. You are reminded of the following: This work is copyright. Apart from any use permitted under the Copyright Act 1968, no part of this work may be reproduced by any process, nor may any other exclusive right be exercised, without the permission of the author. 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Recommended Citation Qiu, Wenbin, Investigation of Iron Selenide Superconducting Thin Films Fabricated by Pulsed Laser Deposition, Doctor of Philosophy thesis, Institute for Superconducting and Electronic Materials, University of Wollongong, 2018. https://ro.uow.edu.au/theses1/433 Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: [email protected] i _____________________________________________________________________________ Investigation of Iron Selenide Superconducting Thin Films Fabricated by Pulsed Laser Deposition A thesis submitted for fulfilment of the requirements for the award of the academic degree DOCTOR of PHILOSOPHY From the UNIVERSITY OF WOLLONGONG By QIU Wenbin B. Eng., M. Sc. Institute for Superconducting and Electronic Materials Faculty of Engineering and Information Sciences University of Wollongong, NSW Australia 6th September 2018 ii _____________________________________________________________________________ Certification of Originality I, Wenbin Qiu, declare that the work presented in this thesis was totally carried out by myself in the Institute for Superconducting and Electronic Materials (ISEM), at the University of Wollongong, NSW, Australia unless otherwise referenced or acknowledged. This document has not been submitted to any other academic institution for a qualification. Wenbin Qiu 6th September 2018 iii _____________________________________________________________________________ Dedication To my beloved family iv _____________________________________________________________________________ Acknowledgements First of all, I would like to express my highest appreciation to my principal supervisor, Dr. Zongqing MA. With the support of his Discovery Early Career Researcher Award (DECRA) project, I experienced a start to my Ph.D. career by receiving comprehensive support from not only my academic supervision, but also my strong financial funding. Dr. MA’s active guidance and encouragement in my work and life are of great significance to me. I really cherish the time that we worked together and made achievements, one after another! I am so pleased to show my gratitude to one of my co-supervisors, Prof. Shi Xue DOU, who is also acting as the director of the Institute for Superconducting and Electronic Materials (ISEM), University of Wollongong (UOW). Prof. DOU is a legend to me as he established the ISEM in 1994 based on his world-leading research power and managed the institute to develop as the state-of-the-art research organization that it is nowadays. Thanks to the world-class scientific platform provided by ISEM, I was able to start my research from a higher level and pursue more meaningful results. In addition, I would like to thank Prof. Dou for accepting my Ph.D. application and recommending me to Dr. Zongqing MA in 2014. His kind support and advice helped me greatly during my Ph. D. study. My sincere thanks to Dr. Md Shahriar Al Hossain, another co-supervisor of mine. Dr. Hossain was always ready to give me valuable help from various aspects, including experimental issues, article suggestions, tips on living, financial support, etc. I really admire his tremendous network management skills, which have promoted the well-developed cooperation between our group and numerous collaborators. I would like to acknowledge Dr. Gilberto Casillas Garcia, Dr. David Mitchell, Mr. Tony Romeo, and Dr. Mitchell Nancarrow for their kind help with technical support with respect to the electron microscopes in the Electron Microscopy Center (EMC), UOW. Their great expertise significantly improved the quality of our works. My cordial gratitude to A/Prof. Germanas Peleckis for offering instrument- related advice, arranging administrative issues, and providing the training on the PPMS and XRD. I sincerely acknowledge Dr. Xun XU and Dr. Dongqi SHI for their technical support in regard to various instruments, Prof. Xiaolin WANG, A/Prof. Zhengxiang CHENG, Dr. Zhi LI, and Dr. Wenping SUN for fruitful discussions and critical v _____________________________________________________________________________ comments on my works, Mr. Robert Morgan, Mr. Paul Hammersley, Mr. John Wilton, and Mr. Mathew Davies for the workshop support, Mrs. Crystal Mahfouz, Mrs. Narelle Badger, Mrs. Naomi Davies, and Mr. Paul Scully for the daily administration and procurement, Mrs. Joanne George and Dr. Candace Gabelish for their responsible management of laboratory safety, and Dr. Konstantin Konstantinov, the Head of Postgraduate Studies (HPS), for providing kind support in regard to higher-degree research. I am grateful to Dr. Tania Silver for the critical reading of my manuscripts and thesis. I would like to thank my friends and colleagues Dr. Dipak Patel, Dr. Jonathan Knott, Dr. Jincheng ZHUANG, Mr. Haifeng FENG, Dr. Özlem Çiçek, Dr. Lina SANG, Mr. Hyunseock Jie, Dr. Chandrasekar Subramaniyam, Dr. Sudipta Pramanik, Mr. Guoqiang ZHAO, Dr. David Cortie, Dr. Feixiang XIANG, Dr. Hong GAO, Dr. Dan ZHANG, Mr. Weiyao ZHAO, Ms. Lei CHEN, Mr. Long REN, Mr. Zhixin TAI, Ms. Yajie LIU, Mrs. Yanhua SUN, Mr. Alaa HAMED, and Mr. Yao LU for their kind support and discussions. My Ph.D. studies would have been far less delightful without you. I owe great thanks to Prof. Chuanbing CAI at Shanghai University for his supervision during my master’s degree and for providing me with the opportunity to study for a Ph.D. in ISEM. I also want to thank my collaborators from Tianjin University, Prof. Yongchang LIU, Ms. Qingshuang MA, Ms. Fang CHENG, Ms. Xin WEN, Ms. Xinhua LI, Ms. Huanhuan ZHAO, Mr. Zhi DONG, and Mr. Nan LIU for their helpful discussions and collaborations. This thesis work has been conducted under the Australian Research Council (ARC) DECRA project (No. DE140101333) of Dr. Zongqing Ma. The tuition and stipend were supported by the University Postgraduate Award (UPA) and the International Postgraduate Tuition Award (IPTA), which were kindly offered by the University of Wollongong. My utmost appreciation to my parents, Mr. Jianliang QIU and Mrs. Panqiu TAO, for bringing me into this world. Very special thanks to my beloved wife, Mrs. Wangweilai XIANG for unconditionally supporting me since the first day we met. What you have sacrificed and compromised over these years deserves my highest compliment! In the end, I would like to express my sincere gratitude to all the people who have supported me so far. Without your selfless endeavors, I would definitely not have been able to complete this thesis. Thank you again for helping me to come through all vi _____________________________________________________________________________ the problems that I have encountered. Live long and prosper! vii _____________________________________________________________________________ Abstract Superconductivity is one of the most attractive research projects in condensed matter physics. Among various types of different superconductors, the family of iron- based superconductors has always been a lively topic since the discovery of the superconductivity in LaFeAsO1-xFx in 2008. The conflict between the necessity of Fe element in this type of superconductor and the superficial thinking on the detrimental effect of ferromagnetism on superconductivity makes iron-based superconductivity both intriguing and unconventionally elusive. In material science, iron selenide (FeSe) is a very promising candidate for exploring the mechanism of iron-based superconductivity due to its having the simplest binary composition and much less toxicity than iron-based superconductors containing As. Since the sign of a dramatically high superconducting transition temperature (Tc) over 77 K in a 1 unit-cell FeSe layer grown on SrTiO3 (STO) substrate was reported in 2012 by a group from China, a flourishing upsurge of FeSe thin films was triggered, and the popularity of superconducting research was rejuvenated. The veil between the scientists and the mystery of iron-based superconductivity

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