"We study the effects of quenched weak disorder on quantum phase transitions in disordered magnets. The presence of disorder in the system can lead to a variety of exotic phenomena, e.g., the smearing of transitions or quantum Griffiths singularities. Phase transitions are smeared if individual spatial regions can order independently of the bulk system. In paper I, we study smeared quantum phase transitions in binary alloys A₁₋ₓBₓ that are tuned by changing the composition x. We show that in this case the ordered phase is extended over all compositions x < 1. We also study the composition dependence of observables. In paper II, we investigate the influence of spatial disorder correlations on smeared phase transitions. As an experimental example, we demonstrate in paper III, that the composition-driven ferromagnetic-toparamagnetic quantum phase transition in Sr₁₋ₓCaₓ RuO₃ is smeared. When individual spatial regions cannot order but fluctuate slowly, the phase transition is characterized by strong singularities in the quantum Griffiths phase. In paper IV, we develop a theory of the quantum Griffiths phases in disordered ferromagnetic metals. We show that the quantum Griffiths singularities are stronger than the usual power-law quantum Griffiths singularities in insulating magnets. In paper V, we present an efficient numerical method for studying quantum phase transitions in disordered systems with O(N) order parameter symmetry in the large-N limit. Our algorithm solves iteratively the large-N self-consistent equations for the renormalized distances from criticality. Paper VI is devoted to the study of transport properties in the quantum Griffiths phase associated with the antiferromagnetic quantum phase transition in a metal. We find unusual behavior of transport properties which is in contrast to the normal Fermi-liquid behavior"--Abstract, page v.
Parris, Paul Ernest, 1954-.
Medvedeva, Julia E.
Kaul, Ribhu, 1979-
Ph. D. in Physics
Missouri University of Science and Technology
Journal article titles appearing in thesis/dissertation
- Composition-tuned smeared phase transitions.
- Disorder correlations at smeared phase transitions.
- Disorder promotes ferromagnetism: Rounding of the quantum phase transition in Sr(1-x)CaxRuO₃.
- Quantum Griffiths singularities in ferromagnetic metals.
- Numerical method for disordered quantum phase transitions in the large-N limit.
- Transport properties in antiferromagnetic quantum Griffiths phases.
xiv, 152 pages
© 2013 David Nozadze, All rights reserved.
Dissertation - Open Access
Phase transformations (Statistical physics)
Quantum theory -- Mathematical models
Magnetism -- Mathematical models
Electronic OCLC #
Nozadze, David, "Quantum phase transitions in disordered magnets" (2013). Doctoral Dissertations. 2033.