Speaker
Thierry Giamarchi (U. of Geneva)
Description
Localized spin systems, and in particular dimer systems,
provide a fantastic laboratory to study
the interplay between quantum effects and the interaction
between excitations. Magnetic field and temperature allow an
excellent control on the density of excitations and various
very efficient probes such as neutrons and NMR are available.
They can thus be used as ``quantum simulators'' to tackle
with great success
questions that one would normally search in itinerant
interacting quantum
systems.
In particular they have provided excellent realizations of
Bose-Einstein condensates [1,2]. This allowed not only to probe
the properties of interacting bosons in a variety of dimensions
but also to study in a controlled way additional effects such as
disorder. If the dimensionality is reduced they also allow
to test in a quantitative way Luttinger liquid physics [3,4,5].
I will discuss these various cases, and show that we have
now good
theoretical tools [6] to make quantitative comparisons with the
experiments.
Finally, how to go from this low dimensional case where the
spins behave essentially as fermions, to the higher dimensional
case where they behave as (essentially free) bosons, is a very
challenging, and experimentally relevant issue.
{\small
\noindent
[1] T. Giamarchi and A. Tsvelik, Phys. Rev. B {\bf 59} 11398
(1999).\\
[2] T. Giamarchi, C. R\"uegg and O. Tchernyshyov, Nat. Phys.
{\bf 4} 198
(2008).\\
[3] M. Klanjsek et al., Phys. Rev. Lett. {\bf 101} 137207
(2008).\\
[4] C. R\"uegg et al., Phys. Rev. Lett. {\bf 101} 247202
(2008).\\
[5] B. Thielemann et al., Phys. Rev. B {\bf 79} 020408(R)
(2009).\\
[6] P. Bouillot et al., arXiv:1009.0840 (2010).}
