Exploration of Quantum Transport Phenomena via Engineering Emergent Magnetic Fields in Topological Magnets (Springer Theses)

This book addresses novel electronic and thermoelectronic properties arising from topological spin textures as well as topologically non-trivial electronic structures. In particular, it focuses on a unique topological spin texture, i.e., spin hedgehog lattice, emerging in a chiral magnet and explore its novel properties which are distinct from the conventional skyrmion lattice, and discusses the possibility of realizing high-temperature quantum anomalous Hall effect through quantum confinement effect in topological semimetal. This book benefits students and researchers working in the field of condensed matter physics, through providing comprehensive understanding of the current status and the outlook in the field of topological magnets. Supervisor’s Foreword Acknowledgments Contents 1 Introduction 1.1 Preface 1.2 Berry Phase and Emergent Electromagnetism 1.3 Berry Phase Engineering in Real Space 1.3.1 Berry Phase in Real-Space 1.3.2 Definition of Topology in Spin Structures 1.3.3 Formation of Multiple-q State 1.3.4 Emergent Electromagnetism and THE 1.4 Berry Phase Engineering in Momentum Space 1.4.1 Momentum-Space Berry Phase and AHE 1.4.2 Gapped Topological Phase and QAHE 1.4.3 Gapless Topological Phase–Dirac and Weyl Semimetals 1.4.4 Towards High-Temperature QAHE 1.5 Purpose of This Thesis References 2 Experimental Methods 2.1 Bulk Crystal Growth 2.1.1 MnSi1-xGex Poly Crystals 2.1.2 Co3Sn2S2 Single Crystal 2.2 Magnetization and Electrical Transport Measurement 2.3 Thermoelectric Measurement 2.4 High-magnetic-field Measurement 2.4.1 Magnetization and Resistivity Measurements 2.4.2 Thermoelectric Measurement 2.5 Neutron Scattering Experiment 2.5.1 Small- and Wide-angle Neutron Scattering Experiment References 3 Topological Transitions Between Skyrmion- and Hedgehog-Lattice States in MnSi1-xGex 3.1 Introduction 3.1.1 Crystal Structure 3.1.2 Generic Aspects of B20-Type Compounds 3.1.3 Cubic-3q Hedgehog Lattice State in MnGe 3.2 Overview of Topological Magnetic Transitions in MnSi1-xGex 3.2.1 Magnetic Period and Direction of q-Vectors 3.3 Topological Magnetic Phases in MnSi1-xGex 3.3.1 Formation of SkL States in xleq0.2 3.3.2 Formation of HL States in x0.4 3.3.3 Spin Textures of Tetrahedral-4q Hedgehog Lattice State 3.4 Topological Hall Effect in MnSi1-xGex 3.4.1 Topological Hall Effect in SKL of x=0.2 3.4.2 Topological Hall Effect in HLs of x=0.6 and 0.8 3.5 Formation Mechanism of Hedgehog Lattice States 3.6 Summary References 4 Giant Magneto-Transport Properties Induced by Spin Fluctuations in MnGe 4.1 Introduction 4.2 Large Magneto-Seebeck Effect in Bulk MnGe 4.2.1 Observation of Field-Induced Large Seebeck Effect 4.2.2 Photoemission Spectroscopy and Band Structure Calculation 4.2.3 Specific Heat and Magneto-Resistivity 4.2.4 High-magnetic-field Measurement 4.3 Large Anomalous Hall Effect from Spin-Chirality Skew Scattering 4.3.1 Observation of Giant Hall Response in MnGe Thin Film 4.3.2 Scaling Relation and Temperature-magnetic-field Profile 4.3.3 Film-Thickness Dependence 4.3.4 Discussion on Other Mechanisms 4.3.5 Comparison with Other Materials 4.4 Summary References 5 Topological Transport Properties of Magnetic Weyl Semimetal Co3Sn2S2 Thin Flake 5.1 Introduction 5.1.1 Magnetic Weyl semimetal Co3Sn2S2 5.2 Synthesis of Co3Sn2S2 Thin Flakes 5.3 Transport Properties of Co3Sn2S2 thin flakes 5.4 Comparison with Band Structure Calculations 5.5 Summary References 6 Summary References