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INFORMATION to USERS This Manuscript Has Been Reproduced INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. A Bell & Howell information Company 300 North Zeeb Road. Ann Arbor. Ml 48106-1346 USA 313/761-4700 800/521-0600 NMR Studies of Alkali Fulleride Superconductors DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the Graduate School of The Ohio State University By Victor A. Stenger, B. S., M. S. The Ohio State University 1996 Dissertation Committee: , Approved by Dr. Charles H. Pennington %• Dr. Thomas R. Lemberger ^ Dr. Daniel L. Cox Adviser Department of Physics UMI Number: 9620075 UMI Microform 9620075 Copyright 1996, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 NMR Studies of Alkali Fulleride Superconductors by Victor A. Stenger. Ph. D. The Ohio State University, 1996 Professor Charles H. Pennington, Adviser There has been much debate over the mechanism of superconductivity in the alkali fulleride superconductors A 3C60 (A - alkali metal). Some researchers think an exotic pairing mechanism, possibly involving an electronic interaction, is manifest in A 3 C60 where others believe that the more prosaic phonon-mediated interaction proposed in the theory of Bardeen, Cooper, and Schrielfer (the BCS theory) is appropriate. Also, if the framework of the BCS theory is indeed proper, there is the issue of identifying the relevant modes of the pairing phonons: either the intermolecular or intramolecular modes. This thesis explores these questions with the use of nuclear magnetic resonance (NMR). We find that the body of NMR data on A 3C60 are consistent within the weak coupling limit of BCS theory with a BCS gap parameter less than or equal to l.OkgTc, suggesting that the intramolecular phonons are responsible for electron pairing iti the superconducting state of A3C60* In addition, we use NMR to probe the normal state of A 3 C60 and find that the electronic properties of A 3Q 0 are that of a normal metal with electron-electron interactions having minor importance. Acknowledgments I would first like to thank my lab colleagues (and friends) for their support and guidance. Thanks to Charles Recchia, Joseph Vance, D.-R. Buffinger, S.-M. Lee, Krzysztof Gomy, Christopher Hahm, Valerie Nandor, and Dr. Joseph Martindale. Thanks also to Armen Ezekeilian, James Reynolds and Dave Robertson. It really makes a difference having a bunch of fun and intelligent people to inspire me on a daily basis. With all of you I made lasting friendships which I value forever. Thank you to Dr. Charles Pennington, it was an honor being your first graduate student. Thanks for teaching me about NMR and about superconductivity, even more so for teaching me how to be enthusiastic and excited about science and have confidence in my own intellect. My ties with you will surely entwine into a deep appreciation as life goes on. Thanks also to Dr. Robin Ziebarth for always taking time out of your day to help by providing me with not only outstanding samples but also outstanding insight. There was absolutely no way my work could have been so prolific without you. Thanks to the faculty in the Physics Department at The Ohio State University. Especially, thanks to Dr. Daniel Cox, Dr. Thomas Lemberger, Dr. Ratnasingham Sooryakumar, Dr. David Stroud, and Dr. John Wilkins. Every member with whom I interacted with at OSU physics was nothing but superb. Thanks to the faculty in the Physics Department at the University of Hawaii: Dr. James Gaines, Dr. Peter Crooker, Dr. Xerxes Tata, Dr. Chester Vauss, and Dr. Frederick Harris. My association with both departments was indeed a privilege. I would finally like to thank my family. Thank you to my lovely wife Helenna, you are truly my inspiration and sunshine. Thank you for sacrificing your time and love for my pursuits. Thank you Mom, your infinite support and wisdom is something that I can always rely on to guide me through life's changes. I would especially like to thank Dad. You are the one who not only taught me about the laws of physics also the laws of life. The path you cleared in front of me has afforded me so many advantages that I humbly hope to make you proud. From one Dr. Stenger to the next I dedicate this thesis to you. Vita Sept. 28, 1966 ................................. Bom, Honolulu, Hawaii 1984 .................................................. Graduated from Iolani High School, Honolulu, Hawaii 1989 .................................................. Bachelor of Science, University of Hawaii at Manoa 1989-1992 ....................................... Teaching Assistant, Department of Physics, The Ohio State University 1993-1995 ....................................... Research Assistant, Department of Physics, The Ohio State University 1993 .................................................. Master of Science, The Ohio State University, Columbus, Ohio Publications 1. V. A. Stenger, C. H. Pennington, D. R. Buffinger, and R. P. Ziebarth, Physical Review Letters 74, 1649 (1995). 2. V. A. Stenger, C. H. Recchia, J. E. Vance C. H. Pennington, D. R. Buffinger, and R. P. Ziebarth, Physical Review B Rapid Communications 48, 9942 (1993). 3. V. A. Stenger, C. H. Recchia, C. H. Pennington, D. R. Buffinger, and R. P. Ziebarth, Journal o f Superconductivity 7,931 (1994). 4. V. A. Stenger, C. H. Pennington, D. R. Buffinger, and R. P. Ziebarth, to be submitted to Physical Review B. 5. C. H. Pennington and V. A. Stenger, submitted to Reviews o f Modem Physics. 6. C. H. Pennington, V. A. Stenger, C. H. Recchia, C. D. Hahm, K. R. Gomy, V. A. Nandor, D. R. Buffinger, S.-M. Lee, and R. P. Ziebarth, to be published in Physical Review B Rapid Communications. 7. D. R. Buffinger, R. P. Ziebarth, V. A. Stenger, C. H. Recchia, and C. H. Pennington, Journal o f the American Chemical Society 115, 9267 (1993). 8. D. R. Buffinger, S.-M. Lee, R. P. Ziebarth, V. A. Stenger, and C. H. Pennington, Recent Advances in the Physics and Chemistry, Proceedings of the 185th Meeting of the Electrochemical Society, May 22-27,1994. Field of Study Major Field: Physics Branches of Research: Condensed Matter Physics Superconductivity Nuclear Magnetic Resonance Research Adviser Charles H. Pennington, Assistant Professor of Physics Research Co-Adviser Thomas R. Lemberger, Professor of Physics Table of Contents Page A bstract ........................................................................................................................ ii Acknowledgments ...................................................................................................... iii V ita................................................................................................................................. v Table of Contents ................................................................................................... vii List of Tables .......................................................................................................... x List of Figures ........................................................................................................ xi Chapter Page I. Introduction ..................................................................................................... 1 II. Alkali Fulleride Superconductors ............................................................. 4 HA. Chapter Overview IIB. Superconductivity HBl. Phenomenology of Superconductivity HB2. The BCS Theory EC. Alkali Fulleride Superconductors IIC1. Fullerenes and Solid C60 HC2. A3C60 HC3. Superconductivity in A 3C60 BC4. Phonons in A 3C60 HC5. The Eneigy Gap in A 3C60 vii III. Nuclear Magnetic Resonance ............................................................... 23 IDA Chapter Overview DIB. NMR of Metals HIBl. The Nuclear Spin Hamiltonian mB2. The Knight Shift 1HB3. The Korringa Relation m e. NMR of Superconductors mCl. Electron Spin Susceptibility mC2. The Hebel-Slichter Peak mC3. NMR of Type II Superconductors HID. NMR Results of Other Groups on A 3C60 IDD1. Knight Shift IHD2. Spin Lattice Relaxation Rate IV. Experimental Methods .......................................................................... 40 IVA. Chapter Overview IVB. Experimental
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