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

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