Neutron scattering studies of Sr(Co1−xNix)2As2, FeSn, CsV3Sb5, and YbMnBi2
| dc.contributor.advisor | Dai, Pengcheng | en_US |
| dc.creator | Xie, Yaofeng | en_US |
| dc.date.accessioned | 2025-01-16T20:56:26Z | en_US |
| dc.date.created | 2024-12 | en_US |
| dc.date.issued | 2024-12-05 | en_US |
| dc.date.submitted | December 2024 | en_US |
| dc.date.updated | 2025-01-16T20:56:26Z | en_US |
| dc.description.abstract | In this thesis, we present several neutron scattering investigations on the complex magnetic and electronic properties of a series of quantum materials, including helical order in Sr(Co1-xNix)2As2, spin excitations in FeSn and CoSn, electron-phonon coupling in charge-density-wave state of CsV3Sb5, vortex lattice in Ta doped CsV3Sb5, and spin chirality in YbMnBi2. Firstly, we investigate magnetic ordering and spin fluctuations in Sr(Co1-xNix)2As2, a quasi-two-dimensional planar magnet. Neutron scattering studies reveal a c-axis incommensurate helical magnetic structure in Sr(Co1-xNix)2As2, with enhanced quasi-2D ferromagnetic spin fluctuations induced by Ni doping. Band structure calculations suggest that this helical order arises from Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions mediated by itinerant electrons, offering insight into the quantum order-by-disorder mechanism near a quantum critical point. Next, we examine spin excitations in the metallic kagome lattice materials FeSn and CoSn. In these systems, destructive quantum interference of electronic hopping paths produces nearly localized electrons, resulting in flat electronic bands. Our neutron scattering measurements uncover well-defined spin waves in FeSn and paramagnetic scattering in CoSn, highlighting the delicate balance between geometric frustration and magnetic order in kagome systems. Furthermore, we observe anomalous non-dispersive excitations, attributed to the scattering from hydrocarbon contamination. We also investigate the electron-phonon coupling in CsV3Sb5, a kagome lattice material exhibiting intertwined CDW and superconductivity. Neutron scattering experiments demonstrate that the CDW in CsV3Sb5 is associated with a static lattice distortion and a sudden hardening of a longitudinal optical phonon mode. This finding underscores the critical role of wave vector-dependent electron-phonon interactions in the CDW order, contributing to our understanding of its coupling with superconductivity in kagome metals. The fourth study focuses on the superconductivity in Ta-doped CsV3Sb5, which exhibits enhanced superconductivity upon suppression of CDW order. Through Small-Angle Neutron Scattering (SANS), we probe the vortex lattice structure and its evolution in the superconducting state of Cs(V0.86Ta0.14)3Sb5. Our results show that the vortex lattice exhibits a strikingly conventional behavior, including a triangular symmetry, conventional 2e pairing, and a field dependent scattering intensity that follows a London model. Our results suggest that optimal bulk superconductivity in Cs(V0.86Ta0.14)3Sb5 arises from a conventional Bardeen-Cooper-Schrieffer electron-lattice coupling. Finally, we investigate the giant anomalous Nernst effect (ANE) and anomalous Hall effect (AHE) in the canted antiferromagnet YbMnBi2. The ab-plane spin canting in YbMnBi2 is believed to break time-reversal symmetry, generating a non-zero Berry curvature that gives rise to the giant ANE and AHE. However, direct evidence for this mechanism has remained elusive, as earlier unpolarized neutron measurements excluded significant moment canting. By leveraging the unique advantages of polarized neutron scattering, which can differentiate magnetic scattering from nuclear scattering, we have uncovered clear evidence of spin chirality persisting at temperatures well above room temperature. Additionally, further neutron scattering measurements have revealed inversion-symmetry breaking and anisotropic spin fluctuations, indicating the presence of Dzyaloshinsky-Moriya interactions that likely drive the observed spin chirality, which in turn underlies the ANE and AHE. Our findings provide a detailed mechanism that directly explains the origins of the giant ANE and AHE in YbMnBi2. Overall, the combination of these works advances the understanding of quantum materials by revealing new insights into the magnetic, electronic, and lattice dynamics of these complex systems. The results presented herein pave the way for future studies on quantum magnetism, unconventional superconductivity, and the development of new materials with novel electronic and magnetic properties. | en_US |
| dc.embargo.lift | 2025-06-01 | en_US |
| dc.embargo.terms | 2025-06-01 | en_US |
| dc.format.mimetype | application/pdf | en_US |
| dc.identifier.uri | https://hdl.handle.net/1911/118204 | en_US |
| dc.language.iso | en | en_US |
| dc.subject | neutron scattering | en_US |
| dc.subject | quantum magnetism | en_US |
| dc.subject | kagome lattice | en_US |
| dc.subject | superconductivity | en_US |
| dc.subject | spin chirality | en_US |
| dc.title | Neutron scattering studies of Sr(Co1−xNix)2As2, FeSn, CsV3Sb5, and YbMnBi2 | en_US |
| dc.type | Thesis | en_US |
| dc.type.material | Text | en_US |
| thesis.degree.department | Physics and Astronomy | en_US |
| thesis.degree.discipline | Physics | en_US |
| thesis.degree.grantor | Rice University | en_US |
| thesis.degree.level | Doctoral | en_US |
| thesis.degree.name | Doctor of Philosophy | en_US |