Study of Electronic Properties of 122 Iron Pnictide Through Structural, Carrier-Doping, and Impurity-Scattering Effects

ISBN-13: 9789811351495 / Angielski / Miękka / 2018 / 88 str.

Tatsuya Kobayashi

Spis treści

1 Introduction

1.1 Iron-Based Superconductor (FeSC)

1.2 Crystal Structure and Magnetic Order of FeSC

1.3 Phase Diagram of FeSC

1.4 Superconducting Property

1.5 Normal State Property

1.6 Aim of This Study

2 Experimental Methods

2.1 Single Crystal Growth

2.2 Transport Measurement

2.3 Magnetization

2.4 X-Ray Diffraction Measurement

2.5 Specific Heat Measurement

2.6 Optical Measurement

3 Electronic Phase Diagram and Superconducting Property of SrFe₂(As_1-xP_x)₂

3.1 Introduction

3.2 Annealing Effect

3.3 Structural Analysis

3.4 Transport Measurement

3.5 Magnetic Susceptibility Measurement

3.6 Electronic Phase Diagram

3.7 Specific Heat in Superconducting State

3.8 Summary

4 In-Plane Resistivity Anisotropy of Ba(Fe_1-xTM_x)₂₂ (TM=Cr, Mn, and Co)

4.1 Introduction

4.2 Resistivity Measurement with Detwinned Crystals

4.3 Hall Effect in Cr and Mn-Ba122

4.4 Relation Between RH and Δρ

4.5 Discussion on the Origin of Resistivity Anisotropy

4.6 Summary

5 Optical Property of Ba(Fe_1-xTM_x)₂As₂ (TM=Cr, Mn, and Co)

5.1 Introduction

5.2 Doping Dependence of Optical Spectra

5.3 Fitting of σ(ω) with Drude-Lorentz Model

5.4 Transition Metal Doping Effect on the AFO State

5.5 Magnetic/Non-magnetic Impurity Effect

5.6 Localized Carrier Induced by Mn/Cr-Doping

5.7 Summary

6 Conclusion

6.1 Structural and Superconductivity Property in P-Sr122

6.2 Resistivity Anisotropy in Ba(Fe_1-xTM_x)₂As₂ (TM=Cr, Mn, and Co)

6.3 Optical Conductivity in TM-Ba122

6.4 Summary

6.5 Future Work

O autorze

Tatsuya Kobayashi is an experimentalist in condensed-matter physics, and his work is concerned with strongly correlated electron systems and iron-based superconductors.

Tatsuya Kobayashi received a Bachelor of Science, Master of Science, and Ph.D. from the Department of Physics, Graduate School of Science, Osaka University in 2011, 2013, and 2016, respectively. During his graduate program, he joined the group led by Professor Setsuko Tajima in the Department of Physics, Osaka University. Between April 2014 and March 2016, he was awarded a research fellowship for young scientists (DC2) by the Japan Society for the Promotion of Science (JSPS), and his research was supported by JSPS.

Blurb

This thesis presents various characteristics of 122-type iron pnictide (FeSC) such as crystal and electronic structure, carrier-doping effect, and impurity-scattering effect, using transport, magnetization, specific heat, single-crystal X-ray diffraction, and optical spectral measurements. Most notably the measurement on the magnetic fluctuation in the material successfully explains already known unusual electronic properties, i.e., superconducting gap symmetry, anisotropy of in-plane resistivity in layered structure, and charge dynamics; and comparing them with those of normal phase, the controversial problems in FeSCs are eventually settled.

The thesis provides broad coverage of the physics of FeSCs both in the normal and superconducting phase, and readers therefore benefit from the efficient up-to-date study of FeSCs in this thesis. An additional attraction is the detailed description of the experimental result critical for the controversial problems remaining since the discovery of FeSC in 2008, which helps readers follow up recent developments in superconductor research.