Optical properties of iron-based multiband conductors and superconductors
Condensed Matter Physics and Materials Science Department
Brookhaven National Laboratory
Upton, New York 11973, USA
In the high-temperature cuprate superconductors, only a single band is
observed at the Fermi level; as a result the optical conductivity may
be modeled using a single free-carrier (Drude) component.
In a simple metal the Drude model is usually sufficient to describe
the frequency-dependent conductivity; however, in the cuprates
electronic correlations and electron-boson coupling require a more
generalized form in which the scattering rate and the effective mass
are both frequency dependent . The iron-based conductors and
superconductors are multiband materials with several bands crossing
the Fermi level, resulting in multiple hole and electron pockets at
the center and corners of the Brillouin zone, respectively . The
presence of multiple bands requires, at a minimum, a "two-Drude" model
in which the electron and hole pockets are treated as separate
contributions . In general, the two-Drude approach reveals: (i) a
strong component associated with the hole pocket with a large
scattering rate (nearly incoherent transport) that is essentially
temperature independent; (ii) a weaker component associated with the
electron pocket whose scattering rate has a strong temperature
dependence. Some recent results using this approach are discussed for
the iron-chalcogenide superconductor FeTe0.55Se0.45 (Tc~14 K)  and
the strongly-correlated parent material Fe1+δ Te (TN~68 K) .
 A. V. Puchkov, D. N. Basov, and T. Timusk, J. Phys.: Condens. Matter 8, 10049 (1996).
 S. Raghu et al., Phys. Rev. B 77, 220503(R) (2008).
 D. Wu et al., Phys. Rev. B 81, 100512 (2010).
 C. C. Homes et al., Phys. Rev. B 81, 180508(R) (2010).
 Y. M. Dai et al., Phys. Rev. B 90, 121114(R) (2014).
*This work done in collaboration with Yaomin Dai, Qiang Li, Jinsheng
Wen, Zhijun Xu, Genda Gu, Ricardo Lobo, and Ana Akrap; work supported
by the US Department of Energy, Office of Basic Energy Sciences,
Division of Materials Sciences and Engineering under Contract