physikalischesK

ollo

quiu

mMo. 28.05.1816:00 UhrOrt: H34

Prof. Dr. Thomas VojtaMissouri University of Science

and Technology,Rolla MO

Exotic phase transitions in disorderedmagnets, superconductors, andultracold gases

Phase transitions are ubiquitous phenomena withapplications ranging from cosmology to biological

systems and to quantum matter at low temperatures.

Many systems that undergo phase transitions containimpurities, defects and other forms of disorder. Recent researchhas shown that even weak disorder can have dramatic effectson the properties of phase transitions. Often, rare disorderfluctuations and rare spatial regions completely dominate thephysics close to the transition.

This talk discusses several examples of exoticbehavior arising at disordered phase transitions.These include the quantum Griffiths phases innickel-vanadium alloys, infinite-randomnesscriticality in superconducting thin films, as wellas the elusive sliding phase realized in ultracoldgases.

In some cases, disorder can completely destroythe phase transition by “smearing”, as has beenobserved, e.g., in strontium-calcium ruthanate.

Randomly substituting Sr atoms by Ca in SrRuO3suppresses the ferromagnetic phase and leads to asmeared quantum phase transition where raremagnetic regions exist in a nonmagnetic bulk.