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Spin Dynamics of Density Wave and Frustrated Spin Systems Probed by Nuclear Magnetic Resonance Lloyd L

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Spin Dynamics of Density Wave and Frustrated Spin Systems Probed by Nuclear Magnetic Resonance Lloyd L Florida State University Libraries Electronic Theses, Treatises and Dissertations The Graduate School 2008 Spin Dynamics of Density Wave and Frustrated Spin Systems Probed by Nuclear Magnetic Resonance Lloyd L. (Lloyd Laporca) Lumata Follow this and additional works at the FSU Digital Library. For more information, please contact [email protected] FLORIDA STATE UNIVERSITY COLLEGE OF ARTS AND SCIENCES SPIN DYNAMICS OF DENSITY WAVE AND FRUSTRATED SPIN SYSTEMS PROBED BY NUCLEAR MAGNETIC RESONANCE By LLOYD L. LUMATA A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree Awarded: Fall Semester, 2008 The members of the Committee approve the Dissertation of Lloyd L. Lumata defended on October 31, 2008. James S. Brooks Professor Directing Dissertation Naresh Dalal Outside Committee Member Arneil P. Reyes Committee Member Pedro Schlottmann Committee Member Christopher Wiebe Committee Member Mark Riley Committee Member Approved: Mark Riley, Chair Department of Physics Joseph Travis, Dean, College of Arts and Sciences The Office of Graduate Studies has verified and approved the above named committee members. ii To my family... iii ACKNOWLEDGEMENTS This is it, like an Oscar called Ph.D. after four and a half years... I would like to express my gratitude, first and foremost, to my advisor Prof. James S. Brooks for being a great mentor in person and in research. He is the type of advisor who can turn a novice, clumsy graduate student into an astute observer and skilled researcher. He is smart, open-minded, responsible, and very helpful to his students and I am honored to be his 23rd Ph.D. graduate. I am indebted to Dr. Arneil Reyes and Dr. Philip Kuhns, the two people who, together with my advisor, formed the triad which contributed much to my scientific education and training throughout my years of study at the National High Magnetic Field Laboratory. Thanks is also extended to Dr. Michael Hoch and Prof. William Moulton for their scientific guidance. It is my pleasure to collaborate and exchange ideas with Prof. Stuart Brown of UCLA Department of Physics. I would like to thank my colleagues Robert Smith, Tiglet Besara, Dr. David Graf, Dr. Takahisa Tokumoto, Dr. Eung Sang Choi, Ade Kismarahardja, Moaz Altarawneh, Eden Steven, and Zach Stegen for their company and assistance at NHMFL. Thanks to my predecessors Dr. Relja Vasic, Dr. Eric Jobiliong, and Dr. Andrew Harter for teaching me how to handle cryogenics and some instrumentation during my first time. Thanks to Dr. Kwang-Yong Choi for his brilliant ideas on hot condensed matter topics. Thanks is extended to Dr. Haidong Zhou and Prof. Chris Wiebe for introducing me to the physics of frustrated spin systems. Furthermore, I would like to thank: John Pucci and Dan Freeman for providing liquid Helium even in short notice for urgent experiments. The staff of DC field control room for giving extra minutes in the high magnetic field experiments. Bruce Brandt and Eric Palm for approving our magnet time proposals. Vaughan and the Machine shop staff for their fine work in making those little brass pieces for our probe and cryostats. iv Alice Hobbs of NHMFL and Sherry Tointigh of the FSU Physics Department for all their help in the paperwoks and reminders. Laurel McKinney and Eva Crowdis for processing my tutorial timesheets. Connie Eudy for giving me an awesome opportunity to be an associate in the Program for Instructional Excellence (PIE). The Hinchliffe family: Pilar, Mark, and Bill for being my family here in Tally. The Filipino-American community for making me feel at home. My friends at Rogers Hall, especially Robin and Wolfgang, for the good ol’ times in Tennessee street. I’ll surely miss the Seminoles playing football at Doak Campbell stadium. Go Noles! The Ong family: Cromwell, Winston, Lionel, Madeleine, and Sir Poly Huang for their brilliant advice and generosity. Prof. Jose Perano and the WMSU Physics family for teaching me perseverance in physics. Thanks to the committee members for perusing this manuscript and for devoting a couple of their precious hours to my dissertation defense. This is also an opportune time to acknowledge the support for this work by the National Science Foundation Division of Materials Research through grants NSF DMR-0602859 and DMR-0654118, the U.S. Department of Energy, and the State of Florida. This dissertation is dedicated to my parents Jose and Evelyn Lumata and to my siblings Richard, Analyn, Edwin, and Jenica. I also dedicate this to Vivienne Anne Santos for her care and inspiration. Above all, I thank the Almighty God for all the blessings He has given me without which I could not have completed this long road to Ph.D. v TABLE OF CONTENTS List of Tables ...................................... viii List of Figures ..................................... ix Abstract ........................................ xvii 1. INTRODUCTION TO NUCLEAR MAGNETIC RESONANCE ........ 1 1.1 Knight Shift: Probing the Internal Magnetism ............... 2 1.2 Hyperfine Coupling Terms of the Interaction Hamiltonian ........ 5 1.3 Measuring the Dynamics: Relaxation Rates ................ 6 1.4 Temperature-dependent Relaxation in Metals ............... 12 1.5 Hebel-Slichter Peak: Test of BCS Superconductivity ........... 15 1.6 NMR Instrumentation ............................ 16 2. AN OVERVIEW OF LOW-DIMENSIONAL ORGANIC CONDUCTORS .. 23 2.1 Low Dimensional Instabilities ........................ 24 2.2 The Bechgaard Salts ............................. 29 2.3 Transport Properties ............................. 33 2.4 Magnetic Properties ............................. 35 2.5 Phase Diagram of (TMTSF)2X ....................... 37 3. SIMULTANEOUS 77Se NMR AND TRANSPORT INVESTIGATION OF THE SPIN DENSITY WAVE SYSTEMS (TMTSF)2X, X=ClO4,PF6 ..... 41 3.1 Experimental Details ............................. 42 3.2 Temperature Dependence of NMR Spectra ................. 46 3.3 The RF Enhancement Factor η ....................... 47 3.4 RF Power dependence of NMR lineshapes in the FISDW State ...... 48 77 3.5 Field Dependence of 1/T1,Rzz, and Spectra at Constant Temperature . 51 77 3.6 Temperature Dependence of 1/T1 at Low Fields ............. 53 3.7 Angular Dependence of 77Se NMR and Transport in the Metallic State . 55 3.8 Angular Dependence of 77Se NMR and Transport in the FISDW State . 57 77 3.9 Temperature Dependence of 1/T1, Spectra, and Rzz at High Fields .. 63 77 3.10 A Comparative Study: Se NMR and Transport on (TMTSF)2PF6 ... 67 3.11 Summary and Conclusion .......................... 72 4. NMR ON CHARGE DENSITY WAVE SYSTEMS ............... 75 vi 4.1 Coexisting CDW and Spin-Peierls States in (Per)2Pt[mnt]2 ........ 75 4.2 Crystal Structure and Electronic Properties ................ 77 4.3 Experimental Details ............................. 78 4.4 Results and Discussion ............................ 78 4.5 Conclusion .................................. 82 4.6 CuxTiSe2: a new CDW-Superconductor .................. 82 4.7 Experimental methods ............................ 84 77 63 4.8 Se and Cu NMR Studies of CuxTiSe2 .................. 85 4.9 Conclusion .................................. 89 5. PROBING THE DYNAMICS OF FRUSTRATED SPIN SYSTEMS ..... 90 5.1 A survey of Frustrated Spin Systems .................... 90 5.2 The Rare-Earth Kagom´eR3Ga5SiO14 .................... 93 69,71 5.3 Ga NMR Probe of the Spin Dynamics of Pr3Ga5SiO14 ........ 93 5.4 Results and Discussion ............................ 96 5.5 Conclusion .................................. 102 93 5.6 Nb NMR Probe of Ba3NbFe3Si2O14 .................... 102 5.7 Conclusion .................................. 110 6. CONCLUSION ................................... 111 6.1 Future Work ................................. 113 REFERENCES ..................................... 115 BIOGRAPHICAL SKETCH ............................. 123 vii LIST OF TABLES 2.1 Broken symmetry ground states of metals: SS-singlet superconductivity, TS- triplet superconductivity, CDW-charge density wave, SDW-spin density wave (from Ref. [12]). .................................. 24 2.2 The Bechgaard Family of Superconductors (from Ref. [9]) .......... 30 4.1 Korringa factor K(α) due to electron-electron interaction in CuxTiSe2 .... 88 6.1 NMR parameters relevant to the work done in this dissertation. ....... 111 viii LIST OF FIGURES 1.1 A simple mechanism of NMR: rf irradiation of the nuclear moment precessing at Larmor frequency. With energy equal to the Zeeman splitting, rf can flip the nuclear spin then it returns to equilibrium releasing a signal. The lower figure represents the energy levels when the field is off or on. ......... 2 1.2 The Knight shift: the resonant frequency of the sample shifts by γBint from the reference due to local internal magnetic field. ............... 3 1.3 The spin-echo pulse sequence: the magnetization is tipped by a 900 pulse and the spins start to “fan out”on the XY plane forming a FID signal. A second pulse flipped the spins 1800 and they regroup then fan out again forming a spin echo signal. .................................. 4 1.4 Measuring the spin-lattice relaxation time T1: (a) a π/2 “saturation” pulse is followed by a variable delay time which allows the growth of longitudinal magnetization Mz as it increases. The π/2 π spin-echo sequence “inspects” the recovery of this magnetization which is reflected− in (b) where the constant of the exponential growth is T1. ......................... 8 1.5 Measuring the spin-spin relaxation time T2: (a) the variable delay time τdelay
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