Abstract:
Organic salt kappa-(BETS)
2
FeBr
4
is a unique compound in which local moment
antiferromagnetism of Fe
3+
ions (below Neel temperature T
N
of 2.5 K)
coexists with
bulk superconductivity (below the superconducting transition temperature
of T
C
=1.1 K).
After a general introduction to the optical properties of conventional
superconductors I will discuss
the results of our experimental investigation of the optical properties
of kappa-(BETS)
2
FeBr
4
in which we probe the temperature regime of the coexistence as well as
the normal state.