Thursday's seminar

[Cond.Matt. & Stat.Mech.Section]

SEMINAR on Disorder and strong electron correlations



Thursday, 4 February      -  11:00 a.m.



  Seminar Room,  Leonardo Building - first floor



Alexei ANDREANOV   ( I.C.T.P. )



"Spin glass transition in geometrically frustrated antiferromagnets  
with weak disorder"



Abstract



We study the effect in geometrically frustrated antiferromagnets of  
weak, random variations in the strength of exchange interactions.   
Without disorder the simplest classical models for these systems have  
macroscopically degenerate ground states, and this degeneracy may  
prevent ordering at any temperature. Weak exchange randomness favours  
a small subset of these ground states and induces a spin-glass  
transition at an ordering temperature determined by the amplitude of  
modulations in interaction strength. We use the replica approach to  
formulate a theory for this transition, showing that it falls into the  
same universality class as conventional spin-glass transitions. In  
addition, we show that a model with a low concentration of defect  
bonds can be mapped onto a system of randomly located pseudospins that  
have dipolar effective interactions.  We also present detailed results  
from Monte Carlo simulations of the classical Heisenberg  
antiferromagnet on the pyrochlore lattice with weak randomness in  
nearest neighbour exchange