## Fermi Surface and Quantum Critical Phenomena of High-Temperature SuperconductorsThis thesis provides a detailed introduction to quantum oscillation measurement and analysis and offers a connection between Fermi surface properties and superconductivity in high-temperature superconductors. It also discusses the field of iron-based superconductors and tests the models for the appearance of nodes in the superconducting gap of a 111-type pnictide using quantum oscillation measurements combined with band structure calculation. The same measurements were carried out to determine the quasiparticle mass in BaFe2(As1-xPx)2, which is strongly enhanced at the expected quantum critical point. While the lower superconducting critical field shows evidence of quantum criticality, the upper superconducting critical field is not influenced by the quantum critical point. These findings contradict conventional theories, demonstrating the need for a theoretical treatment of quantum critical superconductors, which has not been addressed to date. The quest to discover similar evidence in the cuprates calls for the application of extreme conditions. As such, quantum oscillation measurements were performed under high pressure in a high magnetic field, revealing a negative correlation between quasiparticle mass and superconducting critical temperature. |

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### Contents

1 | |

2 Theory | 15 |

3 Experimental Setup | 44 |

4 BaFe2As1xPx2A Quantum Critical Superconductor | 81 |

5 LiFeAs and LiFePStoichiometric Superconductors | 120 |

6 YBa2Cu4O8 | 145 |

Appendix A Numerical Phase Sensitive Detection in Matlab | 160 |

### Other editions - View all

Fermi Surface and Quantum Critical Phenomena of High-Temperature Superconductors CARSTEN MATTHIAS. PUTZKE No preview available - 2018 |

Fermi Surface and Quantum Critical Phenomena of High-Temperature Superconductors Carsten Matthias Putzke No preview available - 2016 |

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agreement amplitude angle anti-ferromagnetic BaFe2(As BaFe2P2 band structure behaviour Carrington caused crystal structure cuprates dashed lines density determined DFT calculations dHvA doped effective mass electron pockets energy experimental extremal orbits Fermi level Fermi liquid Fermi surface Fermi surface sheets Fermi surface topology heat capacity hence High-Temperature Superconductors hole pocket interactions iron-pnictides Kasahara lattice parameter Lett LK formula London penetration depth low temperatures lower critical field magnetic field magnetoresistance Matsuda mean free path measurements nesting NHMFL observed obtained orbital character panel particle mass phase diagram phase transition Phys pnictides pnictogen pnictogen height pulsed magnetic field Putzke quantum critical point quantum oscillations quasiparticle quasiparticle mass resistance sample sensor Shibauchi shown in Fig shows signal single crystals superconducting critical temperature Terashima theory torque typically unit cell upper critical field values vortex YBCO zero