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A Bird's-Eye View of Charge and Spin Density Waves

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A Bird's-Eye View of Charge and Spin Density Waves ADVERTIMENT. Lʼaccés als continguts dʼaquesta tesi doctoral i la seva utilització ha de respectar els drets de la persona autora. Pot ser utilitzada per a consulta o estudi personal, així com en activitats o materials dʼinvestigació i docència en els termes establerts a lʼart. 32 del Text Refós de la Llei de Propietat Intel·lectual (RDL 1/1996). Per altres utilitzacions es requereix lʼautorització prèvia i expressa de la persona autora. En qualsevol cas, en la utilització dels seus continguts caldrà indicar de forma clara el nom i cognoms de la persona autora i el títol de la tesi doctoral. No sʼautoritza la seva reproducció o altres formes dʼexplotació efectuades amb finalitats de lucre ni la seva comunicació pública des dʼun lloc aliè al servei TDX. Tampoc sʼautoritza la presentació del seu contingut en una finestra o marc aliè a TDX (framing). Aquesta reserva de drets afecta tant als continguts de la tesi com als seus resums i índexs. ADVERTENCIA. El acceso a los contenidos de esta tesis doctoral y su utilización debe respetar los derechos de la persona autora. Puede ser utilizada para consulta o estudio personal, así como en actividades o materiales de investigación y docencia en los términos establecidos en el art. 32 del Texto Refundido de la Ley de Propiedad Intelectual (RDL 1/1996). Para otros usos se requiere la autorización previa y expresa de la persona autora. En cualquier caso, en la utilización de sus contenidos se deberá indicar de forma clara el nombre y apellidos de la persona autora y el título de la tesis doctoral. No se autoriza su reproducción u otras formas de explotación efectuadas con fines lucrativos ni su comunicación pública desde un sitio ajeno al servicio TDR. Tampoco se autoriza la presentación de su contenido en una ventana o marco ajeno a TDR (framing). Esta reserva de derechos afecta tanto al contenido de la tesis como a sus resúmenes e índices. WARNING. The access to the contents of this doctoral thesis and its use must respect the rights of the author. It can be used for reference or private study, as well as research and learning activities or materials in the terms established by the 32nd article of the Spanish Consolidated Copyright Act (RDL 1/1996). Express and previous authorization of the author is required for any other uses. In any case, when using its content, full name of the author and title of the thesis must be clearly indicated. Reproduction or other forms of for profit use or public communication from outside TDX service is not allowed. Presentation of its content in a window or frame external to TDX (framing) is not authorized either. These rights affect both the content of the thesis and its abstracts and indexes. Universitat Autònoma de Barcelona Doctoral Thesis A BIRD’S-EYE VIEW OF CHARGE AND SPIN DENSITY WAVES FROM FIRST PRINCIPLES CALCULATIONS Student: Supervisors: Ionel Bogdan Guster Prof. Dr. Pablo Ordejón Prof. Dr. Enric Canadell Dr. Miguel Pruneda Tutor: Dr. Miguel Pruneda A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy in Physics Theory and Simulation Group Catalan Institute of Nanoscience and Nanotechnology Autonomous University of Barcelona June 2019 Declaration of Authorship I, Ionel Bogdan Guster, declare that this thesis titled, ’ A BIRD’S-EYE VIEW OF CHARGE AND SPIN DENSITY WAVES FROM FIRST PRINCIPLES CALCULATIONS’ and the work presented in it are my own. I confirm that: This work was done wholly or mainly while in candidature for a research degree at this University. Where any part of this thesis has previously been submitted for a degree or any other qualification at this University or any other institution, this has been clearly stated. Where I have consulted the published work of others, this is always clearly attributed. Where I have quoted from the work of others, the source is always given. With the exception of such quotations, this thesis is entirely my own work. I have acknowledged all main sources of help. Where the thesis is based on work done by myself jointly with others, I have made clear exactly what was done by others and what I have contributed myself. Signed: Date: ii To Olga iii Man has gone out to explore other worlds and other civilizations withouth having explored his own labyrinth of dark passages and secret chambers, and without finding what lies behind doorways that he himself has sealed.(Solaris) Acknowledgements The PhD metamorphosis was enriched by the many people that I am grateful to have met during these past four years of my life. Firstly, I would like to thank to my thesis advisors, Pablo, Enric and Miguel, for trusting me with the interesting and intellectually provocative projects, for all the knowledge that they have shared with me about physics principles and how to do rigorous scientific work, inspiring me with all the values that comes with it, for their constant feedback, for their motivating enthusiasm for science, for their patience in general. I would like to thank to the collaborators on the papers that we published, espe- cially to Jean-Paul Pouget, who shared from his immense knowledge about density waves, and to Roberto, who always brought a different perspective. To my friends and colleagues from ICN2 with whom I had a good laugh or an interesting discussion, in particular to the friends from the Theory and Simulation group (Lorenzo, Ruben, Sergio, Ramón, Laura, Vladimir, Desanka, Jose, Nick, Ar- salan, Zeila, Matthieu, Nils and many more); to the friends of ICN2 that taught me to play padel or with whom I had a good run in a football game. To my friends and flatmates, Andreea and Lili, with whom I always had a great time in our activities in or outside the flat. To my friends from Bucharest, that always received me with the warmest wel- comes and shared their time with me whenever I stopped by. I would like to thank my family for their unconditional love, support and un- derstanding, for the little time we spent together that made it so much more special. Last but not least, to my partner, Olga, for always being there no matter what, for her infinite patience, for her carrying love and for her believing in me, for the time we spent together to discover the most amazing places around us in our most beautiful years so far. For all this I believe I couldn’t have been in a better place to pursue my PhD work and my passion for physics. vii CONTENTS Declaration of Authorship ii Acknowledgements vii Contents ix List of Figures xiii List of Tables xxiii Abbreviations xxv I Introduction 1 0 Introduction 3 1 Theoretical Background 7 1.1 Electronic structure approaches .................... 7 1.1.1 Density Functional Theory ................... 9 1.1.2 Approximating the Exchange-Correlation . 11 1.1.3 The SIESTA method ...................... 12 1.2 Charge (and Spin) Density Waves ................... 15 II Instabilities in single-layer materials 23 2 Nature of the 2x2 CDW in single-layer TiSe2 27 2.1 Introduction ............................... 27 2.2 Intrinsic single-layer properties ..................... 31 2.3 Influence of doping ........................... 43 2.4 Conclusions ............................... 48 2.5 Computational details ......................... 49 3 2x2 Charge Density Wave in single-layer TiTe2 53 3.1 Introduction ............................... 53 3.2 Results and Discussion ......................... 55 3.3 Conclusions ............................... 68 ix Contents x 3.4 Computational details ......................... 69 4 CDW states coexistence in NbSe2 71 4.1 Introduction ............................... 71 4.2 Results and discussion ......................... 73 4.3 Computational details ......................... 81 III Fermi surface nesting of low-dimensional metals 85 5 A paradigmatic case: K0.3MoO3 91 5.1 Introduction ............................... 91 5.2 Electronic structure of K0.3MoO3 ................... 97 5.3 Quantitative analysis of the Lindhard function . 102 5.3.1 The three individual responses . 102 5.3.2 Electronic parameters of the inter-band nesting process and validation of the weak coupling scenario . 103 5.3.3 Relation with the dynamics of the Peierls transition . 107 5.3.4 Inter-chain coupling . 109 5.4 Critical low frequency phonon branches of K0:3MoO3 . 114 5.5 Comparison with other charge density wave systems . 116 5.6 Concluding Remarks . 120 5.7 Computational details . 121 6 Electronic dimensional crossover and Fermi surface nesting in Bechgaard Salts 123 6.1 Introduction ...............................123 6.2 Electronic Structure . 129 6.3 Analysis of the Lindhard function . 133 6.3.1 (TMTSF)2PF6 . 133 6.3.2 (TMTSF)2NO3 in the absence of AO transition . 137 6.3.3 (TMTSF)2ClO4 in the absence of AO transition . 140 6.3.4 (TMTSF)2NO3 in the AO phase . 144 6.3.5 (TMTSF)2ClO4 in the AO phase . 146 6.4 Discussion ................................147 6.4.1 Electronic dimensional crossover and detailed structure of the Fermi surface ........................147 6.4.2 Relationship with the density wave instability . 150 6.4.3 Relationship with the SDW modulated ground state . 152 6.4.4 Relationship with the mechanism of superconductivity . 154 6.4.5 Relationship with the Field Induced and Magneto-transport Phenomena . 155 6.5 Conclusions ...............................155 6.6 Computational details . 158 Contents xi 7 Origin of the CDW in TaTe4 161 7.1 Introduction ...............................161 7.2 Crystal Structure and Electron Counting . 162 7.2.1 Crystal Structure . 162 7.2.2 Electron counting . 164 7.3 Electronic structure of the average structure . 166 7.4 Structural modulation . 170 7.4.1 Modulated structure . 172 7.5 Conclusions ...............................176 7.6 Computational details . 177 IV Conclusions 179 8 Conclusions 181 A Phonon pattern of doped TiSe2 185 B STM image comparison of TiTe2 186 C Fermi surface warping of Bechgaard salts 188 Bibliography 191 LIST OF FIGURES 1.1 CDW in an ideal linear chain ....................
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