Doctoral Dissertations

Keywords and Phrases

Monte Carlo simulation; Phase transition; Quantum phase transition; Quenched disorder effects; Renormalization group theory; Superfluid-insulator transition


"Disorder can have a wide variety of consequences for the physics of phase transitions. Some transitions remain unchanged in the presence of disorder while others are completely destroyed. In this thesis we study the effects of disorder on several classical and quantum phase transitions in condensed matter systems. After a brief introduction, we study the ferromagnetic phase transition in a randomly layered Heisenberg magnet using large-scale Monte-Carlo simulations. Our results provide numerical evidence for the exotic infinite-randomness scenario. We study classical and quantum smeared phase transitions in substitutional alloys A₁₋ₓBₓ. Our results show that the disorder completely destroys the phase transition with a pronounced tail of the ordered phase developing for all compositions x < 1. In addition, we find that short-ranged disorder correlations can have a dramatic effect on the transition. Moreover, we show an experimental realization of the composition-tuned ferromagnetic-to-paramagnetic quantum phase transition in Sr₁₋ₓCaₓRuO₃. We investigate the effects of disorder on first-order quantum phase transitions on the example of the N-color quantum Ashkin-Teller model. By means of a strong disorder renormalization group, we demonstrate that disorder rounds the first-order transition to a continuous one for both weak and strong coupling between the colors. Finally, we investigate the superfluid-insulator quantum phase transition of one-dimensional bosons with off-diagonal disorder by means of large-scale Monte-Carlo simulations. Beyond a critical disorder strength, we find nonuniversal, disorder-dependent critical behavior"--Abstract, page iv.


Vojta, Thomas

Committee Member(s)

Parris, Paul Ernest, 1954-
Yamilov, Alexey
Medvedeva, Julia E.
Vekhter, Ilya



Degree Name

Ph. D. in Physics


Missouri University of Science and Technology

Publication Date

Spring 2013


xii, 146 pages

Note about bibliography

Includes bibliographical references.


© 2013 Fawaz Y. Hrahsheh, All rights reserved.

Document Type

Dissertation - Open Access

File Type




Subject Headings

Phase transformations (Statistical physics)
Order-disorder models
Quantum theory -- Mathematical models
Ferromagnetism -- Computer simulation
Quantum liquids

Thesis Number

T 10314

Electronic OCLC #


Included in

Physics Commons