Abstract:
Phase transitions are 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.
At 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.