Condensed Matter Seminar Series
Phase Transitions and Disorder: Harris Criterion, Griffiths Singularities, and Smearing
Thomas Vojta
Missouri University of Science and Technology
Thursday January 24, 11:30 am, Room 298, Physics Building
Abstract:
Phase transitions are a fascinating phenomena in nature with
consequences ranging from the large scale structure of the universe to
exotic quantum phases at low temperatures. Many realistic systems
contain impurities, defects, and other forms of quenched disorder. This
talk explores the consequences of such randomness on the properties of
phase transitions. In zero-temperature quantum phase transitions,
randomness can have particularly peculiar and strong effects. Often,
rare strong disorder fluctuations and the rare spatial regions that
support them dominate the physics close to the transition. They give
rise to strong singularities in the free energy, the so-called quantum
Griffiths singularities. In some systems such as metallic magnets, the
effects of rare fluctuations can be even stronger, leading to a
destruction of the phase transition by smearing. We suggest a
classification of these rare region effects based on the effective
dimensionality of the defects, and we illustrate it using examples from
classical, quantum, and nonequilibrium phase transitions.
Hosts: Harold Baranger and Jose Hoyos Neto