SYMMETRIES AND BROKEN SYMMETRIES IN CONDENSED-MATTER PHYSICS
Starts 18 Mar 2004 11:00
Ends 18 Mar 2004 20:00
Central European Time
ICTP
Main Building Room 239
Strada Costiera, 11
I - 34151 Trieste (Italy)
Symmetry and invariance principles have played a vital role in the
development of physics. And just about as ubiquitous as symmetry is the
spontaneous breaking of symmetry. In particular, broken symmetry is the
basic underlying concept of condensed-matter physics. Crystal growth and
other phase transitions are phenomena involving spontaneous breaking of
symmetry. Generalised rigidity, as also topological defects like
dislocations, are some of the consequences of the breaking of symmetry
involved in the formation of a crystal from the highly symmetric fluid
phase. The Curie principle, or rather its generalisation called the
Curie-Shubnikov principle, is the basic symmetry principle of physics. Of
particular interest is the application of this principle to composite
objects made up of equal parts (crystals are examples of such composite
objects because they are made up of equal parts called unit cells). For
such objects the possibility of the manifestation of a new type of
symmetry called latent symmetry has been pointed out recently by the
speaker in his book on ferroic materials. Latent symmetry is that
unexpected extra symmetry which can arise sometimes when two or more
identical objects combine to form a composite in a specific way. The
notion of partial symmetry is familiar in crystallography: it is a local
symmetry, rather than a global symmetry. Subunits of the object may be
related by a partial symmetry, but the object as a whole does not have
that symmetry. By contrast, latent symmetry is that partial symmetry of a
subunit of the basic components of a composite made up of equal parts
which is also a global symmetry of the composite.