Quantum spin fluctuations in antiferromagnetic Mott insulators
Date
2025-02-26
Authors
Journal Title
Journal ISSN
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ORCID
Type
Thesis
Degree Level
Masters
Abstract
The 1986 discovery of high-temperature (high-Tc) superconductivity in a family of materials
called cuprates, with the transition temperature Tc well above the melting point of
nitrogen, has revolutionized technological applications of superconductivity. Today high-Tc
superconducting materials are indispensable for many facets of technology, from high-power
storage to MRI machines to nanoscale devices. However, cuprates are highly complex quantum
materials and the mechanism of high-Tc superconductivity is not yet understood. Understanding
why cuprates make such strong superconductors is key to material designing
towards the goal of achieving room-temperature superconductivity.
Cuprates are layered materials and superconductivity occurs mostly in the copper-oxide
(CuO2) planes. The parent compounds of cuprates are antiferromagnetic Mott insulators,
which become superconducting when the CuO2 planes are doped with holes or electrons. The
consensus today is that antiferromagnetic spin fluctuations play a dominant role in high-Tc
superconductivity in cuprates. Therefore, it is crucial to understand the effects of quantum
spin fluctuations in the cuprate parent compounds.
In this thesis, we study extremely high-precision, resonant inelastic x-ray scattering
(RIXS) as well as inelastic neutron scattering (INS) measurements of the spin-wave excitation
spectrum, namely, the magnon dispersion, in a variety of cuprate parent compounds
in terms of mean field theory on the extended Heisenberg model. RIXS data on the magnon
dispersion of cuprates have previously been fit to the extended Hubbard model. By means
of nonlinear least-square regression, we fit high-resolution RIXS data on the magnon dispersion
in La2CuO4 (LCO) thin films, SrCuO2 (SCO), and CaCuO2 (CCO) directly to the
extended Heisenberg model for the first time. We elucidate the nature of nearest-neighbour
and longer-range exchange interactions in LCO thin films with varying effects of substrates,
SCO, and CCO. For all of the RIXS data studied in this thesis, we show that the plaquette
ring exchange interaction plays a dominant role, most notably in SCO and CCO.
Description
Keywords
Mott Insulator, Cuprate, Superconductor, Superconductivity, Antiferromagnetic, Antiferromagnetism
Citation
Degree
Master of Science (M.Sc.)
Department
Physics and Engineering Physics
Program
Physics