Uniaxial Pressure Study of Charge Density Waves in a High-T꜀ Cuprate Superconductor (Springer Theses)

This book presents comprehensive studies of charge density waves (CDW) in a high-Tc cuprate superconductor using x-ray scattering techniques under uniaxial pressure. Specifically, the work addresses inelastic x-ray scattering studies under uniaxial pressure performed on the underdoped cuprate YBa2Cu3O6.67(p=0.12, Tc=65K) with incoming photon energy in the resonant (E=931.3 eV, Cu-L3 edge) and non-resonant conditions (E=17.794 keV). This is a completely new approach to the investigation of charge density waves. It revealed new features of charge density waves in cuprates, whose properties had previously been inaccessible.. Supervisor’s Foreword Abstract Publications Related to This Thesis Acknowledgements Contents Definitions and Acronyms Definitions Acronyms 1 Introduction References 2 High Temperature Cuprate Superconductors 2.1 Crystal Structure 2.1.1 YBa2Cu3O6+x 2.2 Electronic Structure 2.3 Phase Diagram and Phenomenology 2.3.1 Antiferromagnetism 2.3.2 Superconductivity 2.3.3 Pseudogap 2.3.4 Charge Density Waves References 3 Experimental Methods 3.1 Synchrotron Radiation 3.2 X-Ray Scattering Technique 3.2.1 Thomson Scattering 3.2.2 Dynamical Structure Factor 3.2.3 Experimental Setup 3.3 Uniaxial Strain Technique 3.3.1 Piezoelectric-Based Strain Device 3.3.2 Characterization 3.4 Crystal Preparation 3.4.1 Annealing 3.4.2 Detwinning 3.4.3 Preparation for Strain Experiment References 4 CDW in YBa2Cu3O6.67 Under Uniaxial Pressure: Non-resonant Inelastic X-Ray Scattering 4.1 Background 4.1.1 Electron-Phonon Interaction and CDW in Cuprates 4.1.2 Lattice Pressure Studies of YBCO 4.1.3 Uniaxial Pressure as a New Perturbation Method 4.2 Experiment 4.2.1 Typical IXS Spectrum 4.2.2 Energy Resolution 4.2.3 Momentum Resolution 4.3 Results 4.3.1 Enhancement of 2D-CDW Under Uniaxial Pressure 4.3.2 Emergence of 3D-CDW Under Uniaxial Pressure 4.3.3 Complete Softening of an Optical Phonon at the Onset of the 3D-CDW 4.4 Discussion 4.4.1 Comparison with Magnetic-Field-Induced 3D-CDW 4.4.2 Comparison Between 2D- and Uniaxial-Pressure-Induced 3D-CDW 4.5 Conclusions References 5 CDW in YBa2Cu3O6.67 Under Uniaxial Pressure: Resonant Inelastic X-ray Scattering 5.1 Background 5.2 Experiment 5.2.1 Typical RIXS Spectrum 5.2.2 Energy Resolution 5.2.3 Momentum Resolution 5.3 Results 5.3.1 Confirming the Uniaxial Nature of CDW in Cuprates 5.3.2 Absence of the 3D-CDW Under b-axis Compression 5.3.3 Same Resonance Profile of 2D- and 3D-CDW 5.3.4 Anisotropic Response of the 2D-CDW Under Uniaxial Pressure 5.4 Discussion 5.4.1 Direct Versus Indirect Effects of Uniaxial Pressure 5.4.2 b-axis Compression Does Not Restore the C4-Symmetry: Role of the CuO Chain Layer 5.4.3 Anisotropic and Symmetric Response of the 2D-CDW to Uniaxial Pressure 5.4.4 Uniaxial Pressure Enhances the CDW Perpendicular to the Pressure Direction 5.4.5 Why the 3D-CDW is Observed Only Along the b-axis 5.5 Conclusions References 6 Conclusion