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TT: Tiefe Temperaturen
TT 21: Symposium Frustrated Systems
TT 21.4: Fachvortrag
Montag, 7. März 2005, 15:15–15:40, TU H104
Frustration in ice, spin ice and elsewhere — •Roderich Moessner — CNRS and ENS Paris
Geometrically frustrated magnets are distinguished from more conventional ones by their large ground-state degeneracy, as the ground-state constraint does not lead to a unique low-energy configuration. Thus, even at very low temperatures, strong fluctuations can be present as the magnet explores the space of all ground states. In this talk, we discuss the properties of this low-temperature regime. In particular, we propose two schemes which capture its thermodynamics as well as its correlation functions very accurately. One of them is based on a gauge theory and leads to a magnetostatic effective energy functional. This leads to unusual algebraic correlations which are not indicative of a critical point.
This theory can be applied to ordinary (water) ice as well as its magnetic analogues, the spin ice compounds {Ho,Dy}2Ti2O7. In the latter system, one can observe interesting effects, including ‘missing entropy’, as well as a field-induced tuning of the effective dimensionality from d=3 to d=2.