Charge and Heat Transport Phenomena in Electronic and Spin Structures in B20-Type Compounds

ISBN-13: 9784431556596 / Angielski / Twarda / 2015 / 89 str.

Naoya Kanazawa

Opis

This thesis presents systematic experimental research conducted on chiral-lattice crystals referred to as B20-type germanium compounds, especially focusing on skyrmion spin textures and Dirac electrons. An emergent electromagnetic field observed in MnGe, i.e., a gauge field originating from a topologically winding spin texture, demonstrates a formation of three-dimensional skyrmion crystals. Detection of skyrmions in nano-scale Hall-bar devices made of FeGe is realized by measuring the topological Hall effect, a transport property reflecting emergent fields produced by skyrmions. By measuring the electron-filling dependence of thermopower in CoGe, a pronounced thermoelectric property found in this compound is revealed to stem from the asymmetric density of states appearing at certain levels of Fermi energy in the Dirac electron state. The three main results listed above will contribute to enriching a variety of novel electromagnetic responses of emergent gauge fields in solids, to realizing high-performance skyrmion-based magnetic memory and to designing high-efficiency thermoelectric materials, respectively.

Spis treści

Introduction.- Experimental methods.- Magnetic and transport properties in B20-type germanides.- 3D skyrmion-lattice and topological Hall effect in MnGe.- Skyrmion formation in epitaxial FeGe thin films.- 3D Dirac electrons and large thermoelectric properties in CoGe.- Conclusion.

O autorze

Dr.Naoya Kanazawa
Department of Applied Physics, University of Tokyo
kanazawa@ap.t.u-tokyo.ac.jp

Blurb

This thesis presents systematic experimental research on chiral-lattice crystals referred to as B20-type germanium compounds, especially focusing on skyrmion spin textures and Dirac electrons. An emergent electromagnetic field observed in MnGe demonstrates a formation of three-dimensional skyrmion crystals. Detection of skyrmions in nanoscale Hall bar devices made of FeGe is realized by measuring the topological Hall effect, a transport property reflecting emergent fields produced by skyrmions. By measuring the electron-filling dependence of thermopower in CoGe, a pronounced thermoelectric property in this compound is revealed to stem from the asymmetric density of states appearing at certain levels of Fermi energy in the Dirac electron state.

The three main results named above will contribute to enriching a variety of novel electromagnetic responses of emergent gauge fields in solids, to realizing high-performance skyrmion-based magnetic memory, and to designing high-efficiency thermoelectric materials, respectively.