Transport Properties and Modification of the Flux Pinning in Single Crystal Bismuth Cuprate Superconductors by Janet Ann Cutro B.S.. Rensselaer Polytechnic Institute (1979) M.S., Columbia University (1984) Submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 1997 © Massachusetts Institute of Technology Signature of Author ........................................ .. .... .. -,. ..... Department of Physics 6 May 1997 Certified by .............. ................. ........... /.... Terry P. Orlando Professor of Electrical Engineering Thesis Supervisor Certified by........ ............................... .. ....... .. Mildred S. Dresselhaus Institute Professor Thesis Supervisbr Accepted by .............................................. ...................... Professor George F. Koster ...Chair. Departmental Committee on Graduate Students Science JUN 0 9 1997 Transport Properties and Modification of the Flux Pinning in Single Crystal Bismuth Cuprate Superconductors by Janet Ann Cutro Submitted to the Department of Physics on 6 May 1997, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Abstract Two studies on single crystals of the high temperature cuprate superconductor Bi 2Sr 2CaCu2Os, performed in 1988 and 1990-91 respectively, are presented in their original timeframe. Results are reviewed in a present day context at the end of the thesis. Detailed measurements of the angular and temperature dependence of the magnetic field- induced resistive transition are reported. Resistance is observed in the sample for small values of applied field (f 100 Oe) even at low current densities (< 10 A/cm2). This suggests that the resistive transition does not directly reflect the upper critical field of the superconductor, but is complicated by flux-flow effects. The angular dependence of the resistive transition cannot be fit by any standard model for anisotropic fields in superconductors, and anisotropic ratios as large as 50 are found for fields applied perpendicular and parallel to the c-axis of the crystal, in- dicating a large difference in the viscosity for flux motion in the two directions. Current-voltage characteristics for fields applied parallel to the c-axis are linear for low currents at temperatures above 77 K. The shape remains relatively unchanged until the field is within about 200 of the a-b planes, where there is a sudden change to more threshold-like behavior. It has been suggested that the extreme anisotropy of the strongly layered high-temperature superconductors poses intrinsic limitations to the critical current, arising from a short corre- lation length along the vortex axis (pancake vortices). In the second set of experiments, this possible materials limitation is addressed through the introduction of irradiation induced de- fects. A comparative study is presented of the flux pinning in single crystal Bi2Sr 2CaCu2Os before and after irradiation by II-, Ie- , Ne, miand Ar- at incident energies in the MeV range. Irradiation conditions were chosen to hold the total calculated vacancy production by each ionic species approximately constant, and the crystals were sufficiently thin as to assure nearly complete penetration. A significant increase in the pinning energy is found after irradiation by the heavier ions, while light ion (H1, He -) irradiations result in pinning energies comparable to those of unirradiated crystals. As a result of higher pinning energies, critical currents were observed to persist at markedly higher temperatures and fields. The Ar4 dose dependence of the magnetization Jc exhibits a temperature independent but field dependent peak, which is indicative of a classical matching effect. The inter-vortex spacing at the matching field is not consistent with an estimate of defect spacing based upon a model of damage by vacancy pro- duction. It is suggestive rather of the presence of a lower density of relevant defects which act as effective pinning centers, such as would result from a small fraction of high energy recoil events producing damage cascades, rather than simple vacancies. Calculations of recoil energy spectra quantitatively support the existence of cluster-like defects in heavier ion irradiated samples. The dominance of low energy recoils in primary knock-on spectra of H' and He', however, implies a predominance of point defects in light ion irradiated samples. Spatially extended defects can interact with longer sections of the vortices and lead to a higher pinning energy. Thesis Supervisor: Terry P. Orlando Title: Professor of Electrical Engineering Thesis Supervisor: Mildred S. Dresselhaus Title: Institute Professor Acknowledgments The length of this project, with its many interruptions and leaves of absence, makes it espe- cially challenging to thank everyone properly or in the right order. I have had three outstanding advisors while at MIT, but I feel it fitting to start at the end and work my way backwards. I would first like to thank Professor Terry Orlando for taking on an unexpected student, and having the patience to allow me to continue to work intermittently on this thesis, in spite of many indications that it would never be finished. I greatly admire Terry for his uncommon and obvious sense of integrity, as well as his surreptitious sense of humor, and agile mind. He also has a gift for teaching classes with a flair worth missing sleep for, with or without the bribery of doughnuts. I am deeply grateful to him for taking my chapters from under his office door, and will always remember his kindness to me. Professor David Rudman was the principle advisor of this project from its inception through the experimental stages, publications, and the beginning of the writing of this thesis. I thank him for countless acts of generosity in the process of introducing me to the unfamiliar field of high-temperature superconductivity. His support was instrumental to the success of this project. He also taught me that legendary feats of experimental and presentational prowess are possible, armed with a Coke (caffeinated, of course) in one hand. I am sincerely grateful to Dave for continuing to advise this project through my leaves of absence and even from Colorado after his departure from MIT. It was also my unexpected pleasure to be properly congratulated by the old gang after my defense, because Dave made sure they heard the news. To my collaborators at what is now Lucent Technologies, I express my heartfelt thanks. Drs. Bruce van Dover, Lynn Schneemeyer and Alice White opened their facilities to me and gave generously of their time, expertise and encouragement. They are experimentalists extra- ordinaire and extraordinary people. I esp)ecially thank Bruce for sharing his lab and carefully developed experimental techniques with me, and Lynn for her unsurpassed skills in growing state-of-the-art crystals. I thank Dr. Mike Gyorgy for the use of his balance and vibrating sample magnetometer. Bruce and Lynn also gave me patient instruction and help with tiny fragile samples and huge resilient frustrations. P.S. The roses were absolutely beautiful! Prior to the beginning of this project, the late Professor David Adler made it possible for me to come to MIT, and advised and supported me through the beginning of my academic career in amorphous silicon research. I thank him for lively political discussions, the best group dinners to ever dishevel a Chinese restaurant, and a host of other contributions to my professional and personal well-being. His door was always open and his enthusiastic devotion to physics never interfered with his attention and affection for the people around him. Professors Millie Dresselhaus and Takashi Imai carefully read and commented upon this thesis, and offered criticism which was of great value to me. I also thank Millie especially for rejoining my thesis committee after my long absence from MIT, and simply for setting an outstanding example for women in science. At the very beginning of this project, Dr. Jenlh-Yih Juang patiently taught me how to do "magnet runs". Juang was always calm and encouraging, and he tried to teach me not to worry about the small stuff. I've almost got it, Juang. At the Francis Bitter National Magnet Lab, I would like to thank Bruce Brandt, Larry Rubin and Jean Morrison for helping to make magnet runs go as smoothly as possible. I especially thank Professor George Koster for providing me with funding from the Physics I)epartment during some crucial transitions in my student career, and Peggy Berkowitz and Pat Solakoff for their willing and kind help throughout. Over the time I spent at MIT, I greatly enjoyed the company of my fellow students and friends. It has been many years, and so at the risk of leaving someone out I thank, for discus- sion and companionship, Mary MhatthiescAn, Katy Barmak, Kevin Coffey, Lenny Rubin, Dave Dombrowski and John Kucera. Before that, in Dave Adler's group I benefited greatly from the knowledge and camaraderie of Pat Cullen, Camille Fuleihan, Jean-Jacques Hajjar, Angela Odoardi (Mickunas), and my very dear and current friend, Kathleen Tokuda. Outside of MIT, I have been warmly supported by the love of my family and friends, es- pecially my parents, grandparents, brothers, Ann L., my cousin Lucy, Lin-Lin, Nancy, Anabel, Tom Y., Margie W., Edmund, Lee W., Ellen, Sandi, Greta, Ron, Dora, Koren, and my newest and most delightful relatives, Nina, Moriah, and Galen. I thank my old friends from RPI, IBM and Columbia who have checked in on me from time to time, and who are not mentioned by name only because the list would fill a new chapter. To my new friends, especially those who share my house with me, thanks for enduring my recent preoccupation with the completion of this project, to the exclusion of things like keeping the electricity on. I give special thanks to the very dear Ted Scourtis, who has waited patiently for the immi- nent return of romance and music to our lives. I owe a profound debt of gratitude to my best friend and fellow ex-IBM engineer, Dr.