Interplay of Spin, Charge, and Lattice in Kagome Antiferromagnet FeGe
| dc.contributor.advisor | Dai, Pengcheng | |
| dc.contributor.advisor | Yi, Ming | |
| dc.creator | Teng, Xiaokun | |
| dc.date.accessioned | 2024-08-30T16:22:02Z | |
| dc.date.created | 2024-08 | |
| dc.date.issued | 2024-08-08 | |
| dc.date.submitted | August 2024 | |
| dc.date.updated | 2024-08-30T16:22:02Z | |
| dc.description.abstract | Strongly correlated quantum materials feature complex phase diagrams with intertwined phases that have nearly degenerate ground-state energies. A notable example is copper oxides, where charge density waves (CDWs) coexist with magnetic order and compete with superconductivity. Recently, similar rich phase diagrams have been observed in correlated topological materials such as 2D kagome lattice metals. These materials are composed of corner-sharing triangles exhibiting flat bands, magnetic order, superconductivity, and CDW order. In this thesis, we present the discovery of CDW in the antiferromagnetic (AFM) ordered phase of kagome lattice FeGe (Chapter 3). This marks the first observation of CDW in a correlated magnetic-ordered kagome metal. The CDW in FeGe occurs at wavevectors identical to those in the non-magnetic $\rm AV_3Sb_5$ (A = K, Rb, Cs) and enhances the AFM ordered moment. Our findings suggest that the CDW in FeGe arises from electron correlations-driven AFM order and Van Hove singularities-driven instability, contrasting with copper oxides and nickelates where CDW typically precedes or accompanies magnetic order. Using angle-resolved photoemission spectroscopy (ARPES), we identified all three electronic signatures of the kagome lattice in FeGe (Chapter 4). This includes flat bands induced by destructive interference of electronic wavefunctions, topological Dirac crossings, and Van Hove singularities. Below antiferromagnetic transition temperature, driven by magnetic exchange splitting, Van Hove singularities move near the Fermi level, and gaps open in the vicinity of the CDW transition. This behavior highlights the interplay between charge order and magnetism in FeGe. These observations suggest that magnetic interactions drive band modifications, resulting in the formation of the charge density wave, indicating that emergent magnetism and charge order are intertwined in this moderately correlated kagome metal. We then further investigated the spin and lattice excitations in FeGe using inelastic neutron scattering (Chapter 5). Our results show that spin excitations below around 100 meV can be modeled by a spin-1 Heisenberg Hamiltonian. However, higher energy excitations are centered around the Brillouin zone boundary, appearing rod-like, and extend to around 180 meV, consistent with quasiparticle excitations across spin-polarized electron-hole Fermi surfaces. This supports that FeGe is a Hund’s metal in the intermediate correlated regime, with magnetism arising from both itinerant and localized electrons. Moreover, The $c$-axis spin wave dispersion and Fe-Ge optical phonon modes harden below the CDW transition temperature $T_{\rm CDW}$ due to spin-charge-lattice coupling. In addition to these findings, this thesis includes an introduction to the fundamental concepts of magnetism, charge density waves, and the unique properties of kagome materials (Chapter 1). It also details experimental techniques, such as elastic, inelastic neutron scattering, and ARPES (Chapter 2). Overall, this research advances our understanding of the interplay between magnetic, electronic, and structural properties in correlated kagome materials and motivates future studies to further examine the competing phases in these systems. | |
| dc.embargo.lift | 2030-08-01 | |
| dc.embargo.terms | 2030-08-01 | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.uri | https://hdl.handle.net/1911/117782 | |
| dc.language.iso | en | |
| dc.subject | Magnetism | |
| dc.subject | Charge Density Waves | |
| dc.subject | Neutron Scattering | |
| dc.subject | Angle-Resolved Photoemission Spectroscopy | |
| dc.title | Interplay of Spin, Charge, and Lattice in Kagome Antiferromagnet FeGe | |
| dc.type | Thesis | |
| dc.type.material | Text | |
| thesis.degree.department | Physics and Astronomy | |
| thesis.degree.discipline | Physics | |
| thesis.degree.grantor | Rice University | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy |