arXiv subjects

A. Faridian

Publications and source records attributed to A. Faridian.

3 recordsLinked to original sources

arXiv2009

Universal Decomposition of the Low-Frequency Conductivity Spectra of Iron-Pnictides Uncovering Fermi-Liquid Behavior

Infrared reflectivity measurements on 122 iron-pnictides reveal the existence of two electronic subsystems. The one gapped due to the spin-density-wave transition in the parent materials, such as EuFe$_2$As$_{2}$, is responsible for superconductivity in the doped compounds, like Ba(Fe$_{0.92}$Co$_{0.08})_2$As$_{2}$ and Ba(Fe$_{0.95}$Ni$_{0.05})_2$As$_{2}$. Analyzing the dc resistivity and scattering rate of this contribution, a hidden $T^2$ dependence is found, indicating that superconductivity evolves out of a Fermi-liquid state. The second subsystem gives rise to incoherent background, present in all 122 compounds, which is basically temperature independent, but affected by the superconducting transition.

cond-mat.supr-con↗

arXiv2009

Superfluid density of Ba(Fe$_{1-x}M_x$)$_2$As$_2$ from optical experiments

The temperature dependence of the $ab$-plane optical reflectivity of Ba(Fe$_{0.92}$Co$_{0.08})_2$As$_{2}$ and Ba(Fe$_{0.95}$Ni$_{0.05})_2$As$_{2}$ single crystals is measured in a wide spectral range. Upon entering the superconducting regime, the reflectivity in both compounds increases considerably at low frequency, leading to a clear gap in the optical conductivity below 100 cm$^{-1}$. From the analysis of the complex conductivity spectra we obtain the penetration depth $λ(T)=(3500\pm 350)$ Åfor Ba(Fe$_{0.92}$Co$_{0.08})_2$As$_{2}$ and $(3000\pm 300)$ Åfor Ba(Fe$_{0.95}$Ni$_{0.05})_2$As$_{2}$. The calculated superfluid density $ρ_s$ of both compounds nicely fits the scaling relation $ρ_s=(125\pm 25)σ_{dc}T_c$.

cond-mat.supr-con↗

arXiv2009

Effects of the magnetic orderings on the dynamical conductivity: optical investigations of EuFe$_2$As$_2$ single crystals

The magnetic, transport and optical properties of EuFe$_2$As$_2$ single crystals have been investigated parallel and perpendicular to the $ab$-plane. The anisotropy $ρ_c/ρ_{ab}\approx 8$ depends only slightly on temperature. In both orientations, the spin-density wave transition at $T_{\rm SDW}=189$ K shows up as a considerable increase in the dc resistivity. Susceptibility measurements evidence the magnetic order of the Eu$^{2+}$ moments at $T_N=19$ K with little influence on the electronic transport taking place in the FeAs layers. Polarization-dependent infrared spectroscopy reveals strongly anisotropic optical properties and yields a carrier density of only $4.2\times 10^{21} {\rm cm}^{-3}$ and a bandmass of $m_b=2m_0$. A sizeable Drude contribution is present at all temperatures and narrows upon cooling. Below $T_{\rm SDW}$, the spin-density-wave gap develops in the in-plane optical conductivity; no appreciable change is detected for the perpendicular polarization. Modifications in the phonon features are associated with changes of the electronic properties at $T_{\rm SDW}$. The extended Drude analysis yields a linear behavior of the frequency-dependent scattering rate below $T_{\rm SDW}$, indicating an interaction between the charge carriers and spin fluctuations in the spin-density-wave state.

cond-mat.supr-con↗