Excitation Spectra of Square Lattice Antiferromagnets

Authors: Dalla Piazza, Bastien
Nominated as an outstanding Ph.D. thesis by the École Polytechnique Fédérale de Lausanne (EPFL), Switzerland
Presents new theoretical framework explaining anomaly in neutron scattering from square lattice antiferromagnet
Derives effective low-energy theory to describe magnetic excitation spectra of a range of cuprate materials

This thesis presents a qualitative advance in our understanding of quantum effects in layered magnetic materials. The nearest neighbor Heisenberg ferromagnetic ranks among the oldest and most fundamental models of quantum many body effects. It has long been established that in one dimension quantum fluctuations lead to a quantum disordered ground state with fractional excitations called spinons." In two dimensions, the ground state of the Heisenberg model displays static order and to first approximation the dynamics can be described as semi-classical spin waves. Through theoretical advances the author demonstrates that at high energy around particular points in reciprocal space these semi-classical spin-waves deconfine into fractional excitations akin to the one-dimensional spinons. He thereby provides the first explanation of a long-standing experimental observation.
In the second half of his thesis Bastien Dalla Piazza develops a unified description of the magnetic excitation spectra of a range of cuprate parent compounds to the high temperature superconductors

Number of Illustrations and Tables
57 illus., 14 in colour
Topics
Magnetism, Magnetic Materials
Quantum Information Technology, Spintronics
Quantum Physics
Optical and Electronic Materials

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