Physikalisches Kolloquium

Dr. J. Hlinka 

FZU-Institute of Physics of the Czech Academy of Science, Prague, Czech Republic 

Macroscopic symmetry breaking

Abstract:

We are living in the era of powerfull experimental and computational tools allowing us to reach incredibly
detailed insights into the microscopic mechanisms behind specific physical properties of virtually any
crystalline material at the atomic and subatomic lengthscales. The representation theory of
crystallographic space groups and their magnetic counterparts is not only a natural underlying framework
allowing to simplify calculations, to classify the materials, to develop models or to interpret the properties,
but also because many of the most fundamental condensed matter phenomena are directly related to the
real or virtual symmetry breaking phase transitions.

Neverthless, many of the currently studied or exploited properties are related to the materials response
to the perturbations varying at the lengthscales larger than that of the crystal structure unit cell itself. Such
macroscopic properties have to comply with the macroscopic crystalline symmetry that is described by
crystallographic point groups. Dealing with the point groups is obviously much easier then with the space
groups and it is therefore instructive to explore what can be inferred from the macroscopic symmetry
breaking alone. In this talk, we are aiming to explore the concept of classification of species of group-
subgroup pairs within crystallographic point groups and their magnetic counter parts. Among others, the
Aizu concept of species can be used to discuss scalar, vectorial and tensorial properties of multiferroic
domains and domain walls.