Tuning Interactions in Correlated Electron Systems: From Two-Band Superconductivity to Quasi-1D Spin Chains
Alshemi, Ahmed LU
(2024)
- Abstract
- Neutron scattering techniques have been employed to investigate two key areas of condensed matter physics: superconductivity and quantum magnetism. The experimental studies span two distinct areas: two-band superconductors, where we explore the interplay between superconducting anisotropy and vortex structure, and quasi-one-dimensional (quasi-1D) spin chains, where we investigate the magnetic excitations.
In the first part of this thesis, small-angle neutron scattering is used to probe the vortex lattice structure in 2H-NbSS and 2H-NbSe2. In type II superconductors, the application of a magnetic field results in the formation of a well-ordered array of quantized magnetic vortices, known as the vortex lattice. We have investigated the... (More) - Neutron scattering techniques have been employed to investigate two key areas of condensed matter physics: superconductivity and quantum magnetism. The experimental studies span two distinct areas: two-band superconductors, where we explore the interplay between superconducting anisotropy and vortex structure, and quasi-one-dimensional (quasi-1D) spin chains, where we investigate the magnetic excitations.
In the first part of this thesis, small-angle neutron scattering is used to probe the vortex lattice structure in 2H-NbSS and 2H-NbSe2. In type II superconductors, the application of a magnetic field results in the formation of a well-ordered array of quantized magnetic vortices, known as the vortex lattice. We have investigated the vortex lattice in 2H-NbS2 and the effect of the superconducting anisotropy on it by changing the magnetic field orientation relative to the Nb planes. The distortions within the vortex lattice were used to establish the underlying superconducting anisotropy in the system, and we were also able to determine the two characteristic superconductor length scales.
In 2H-NbSe2, the vortex lattice forms with the magnetic field applied parallel to the c-axis, revealing clear evidence of two distinct coherence lengths that characterize the superconducting state. Field-dependent measurements demonstrate the presence of two distinct superconducting bands, providing compelling support for multiband superconductivity in this material.
The second part of the thesis looks at quantum magnetism in quasi-1D antiferromagnetic spin chains, specifically SrCo2V2O8. In such systems, the interplay between strong antiferromagnetic interactions and spin-orbit coupling leads to unique quantum phenomena. The ground state features an Ising-like spin alignment along the chain, while excitations manifest as spinons, fractional quasiparticles that form a continuum. Under certain conditions, the system transitions into a Tomonaga-Luttinger liquid (TLL) phase, characterized by algebraically decaying spin correlations and collective excitations driven by enhanced quantum fluctuations.
Through inelastic neutron scattering, we investigated the effects of a longitudinal magnetic field on magnetic excitations at very low temperatures, where the significance of even small three-dimensional (3D) interactions extends beyond the Tomonaga-Luttinger Liquid (TLL) framework. Additionally, we examined how pressure influences magnetic excitations in SrCo2V2O8, affecting both inter- and intra-chain interactions and impacting the Néel and TLL states. Our results indicate that the Néel state persists to slightly higher fields under pressure, suggesting an enhancement in the energy scale of antiferromagnetic correlations, which increases the spin gap or modifies the nature of the low-energy excitations.
This study provides valuable insights into the impact of magnetic ordering and hydrostatic pressure on TLL spin dynamics. Specifically, we observed that magnetic ordering, including the emergence of longitudinal spin density wave (LSDW) and transverse antiferromagnetic (TAFM) phases, significantly alters TLL excitations, causing deviations from ideal one-dimensional behavior due to interchain interactions. Under hydrostatic pressure, the spinon excitation gap increases, and the critical magnetic fields shift, stabilizing the Néel ordered state. Nonetheless, TLL excitations remain notably robust, with pressure primarily affecting their spectral lineshape rather than the fundamental energy structure. These findings emphasize the complex interplay between one-dimensional quantum spin dynamics, three-dimensional magnetic ordering, and external pressure. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/1f637dd1-f8e1-478d-ad2e-b9721ece5423
- author
- Alshemi, Ahmed
LU
- supervisor
- opponent
-
- Professor Ring Eskildsen, Morten, University of Notre Dame, US.
- organization
- publishing date
- 2024
- type
- Thesis
- publication status
- published
- subject
- keywords
- Superconductivity, Quantum magnetism, Neutron scattering, Condensed matter physics, vortex lattice, one dimensional spin systems
- pages
- 156 pages
- publisher
- Lunds universitet
- defense location
- Rydbergsalen, Department of Physics Join via zoom: https://lu-se.zoom.us/j/68175955162
- defense date
- 2024-12-13 09:15:00
- ISBN
- 978-91-8104-282-5
- 978-91-8104-283-2
- language
- English
- LU publication?
- yes
- id
- 1f637dd1-f8e1-478d-ad2e-b9721ece5423
- date added to LUP
- 2024-11-18 11:16:53
- date last changed
- 2025-04-04 13:54:55
@phdthesis{1f637dd1-f8e1-478d-ad2e-b9721ece5423,
abstract = {{Neutron scattering techniques have been employed to investigate two key areas of condensed matter physics: superconductivity and quantum magnetism. The experimental studies span two distinct areas: two-band superconductors, where we explore the interplay between superconducting anisotropy and vortex structure, and quasi-one-dimensional (quasi-1D) spin chains, where we investigate the magnetic excitations.<br/>In the first part of this thesis, small-angle neutron scattering is used to probe the vortex lattice structure in 2H-NbSS and 2H-NbSe2. In type II superconductors, the application of a magnetic field results in the formation of a well-ordered array of quantized magnetic vortices, known as the vortex lattice. We have investigated the vortex lattice in 2H-NbS2 and the effect of the superconducting anisotropy on it by changing the magnetic field orientation relative to the Nb planes. The distortions within the vortex lattice were used to establish the underlying superconducting anisotropy in the system, and we were also able to determine the two characteristic superconductor length scales.<br/><br/>In 2H-NbSe2, the vortex lattice forms with the magnetic field applied parallel to the c-axis, revealing clear evidence of two distinct coherence lengths that characterize the superconducting state. Field-dependent measurements demonstrate the presence of two distinct superconducting bands, providing compelling support for multiband superconductivity in this material.<br/><br/>The second part of the thesis looks at quantum magnetism in quasi-1D antiferromagnetic spin chains, specifically SrCo2V2O8. In such systems, the interplay between strong antiferromagnetic interactions and spin-orbit coupling leads to unique quantum phenomena. The ground state features an Ising-like spin alignment along the chain, while excitations manifest as spinons, fractional quasiparticles that form a continuum. Under certain conditions, the system transitions into a Tomonaga-Luttinger liquid (TLL) phase, characterized by algebraically decaying spin correlations and collective excitations driven by enhanced quantum fluctuations.<br/><br/>Through inelastic neutron scattering, we investigated the effects of a longitudinal magnetic field on magnetic excitations at very low temperatures, where the significance of even small three-dimensional (3D) interactions extends beyond the Tomonaga-Luttinger Liquid (TLL) framework. Additionally, we examined how pressure influences magnetic excitations in SrCo2V2O8, affecting both inter- and intra-chain interactions and impacting the Néel and TLL states. Our results indicate that the Néel state persists to slightly higher fields under pressure, suggesting an enhancement in the energy scale of antiferromagnetic correlations, which increases the spin gap or modifies the nature of the low-energy excitations.<br/><br/>This study provides valuable insights into the impact of magnetic ordering and hydrostatic pressure on TLL spin dynamics. Specifically, we observed that magnetic ordering, including the emergence of longitudinal spin density wave (LSDW) and transverse antiferromagnetic (TAFM) phases, significantly alters TLL excitations, causing deviations from ideal one-dimensional behavior due to interchain interactions. Under hydrostatic pressure, the spinon excitation gap increases, and the critical magnetic fields shift, stabilizing the Néel ordered state. Nonetheless, TLL excitations remain notably robust, with pressure primarily affecting their spectral lineshape rather than the fundamental energy structure. These findings emphasize the complex interplay between one-dimensional quantum spin dynamics, three-dimensional magnetic ordering, and external pressure.}},
author = {{Alshemi, Ahmed}},
isbn = {{978-91-8104-282-5}},
keywords = {{Superconductivity; Quantum magnetism; Neutron scattering; Condensed matter physics; vortex lattice; one dimensional spin systems}},
language = {{eng}},
publisher = {{Lunds universitet}},
school = {{Lund University}},
title = {{Tuning Interactions in Correlated Electron Systems: From Two-Band Superconductivity to Quasi-1D Spin Chains}},
url = {{https://lup.lub.lu.se/search/files/200067208/Thesis_Ahmed_Alshemi_LUCRIS.pdf}},
year = {{2024}},
}