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https://hdl.handle.net/2142/23376
Description
Title
Magnetism in strongly correlated electron systems
Author(s)
Barzykin, Victor Vadimovich
Issue Date
1995
Doctoral Committee Chair(s)
Pines, David
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Language
eng
Abstract
This thesis consists of two parts, in which I consider two very different examples of magnetism in strongly correlated electron systems, the high-T$\sb{c}$ materials and heavy fermions.
"In the first part, I study the magnetic properties of the high temperature superconductors, using both microscopic models and phenomenology based on the nuclear magnetic resonance and neutron scattering data. The resulting theory proposes a universal phase diagram of the magnetic behavior of the high temperature superconductors and related non-superconducting materials. While the overdoped materials exhibit nearly antiferromagnetic Fermi liquid behavior, for which the mean field description is appropriate, I show, on the basis of NMR experiments, that scaling develops in the underdoped metallic cuprate superconductors, once the antiferromagnetic correlation length exceeds a certain value, $\xi\sb{cr}\simeq2$. In the scaling regime, the value of the dynamical critical exponent is $z=1$, which is a consequence of spin waves present in the excitation spectrum. I show that the region of scaling on the phase diagram coinsides with the region of the so-called ""spin pseudogap"" behavior, which has been observed in many experiments."
In the second part I consider the possible origin of small magnetic moment in some heavy fermion compounds. Apart from their heavy carrier mass, UPt$\sb3$ and URu$\sb2$Si$\sb2$ exhibit antiferromagnetic long range order with very small average values of magnetic moment, $\mu\sim0.01\mu\sb{B}$. I propose that such transitions are driven by an order parameter which is more complicated than that used for ordinary antiferromagnetism, and that the small antiferromagnetic moment appears as a second order effect as a result of the Dzyaloshinskii-Moriya-type interaction. In this thesis, I derive the complete symmetry classification of such states. I also propose methods of experimental verification of the symmetry of the order parameter.
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