Optical conductivity of iron-based superconductors

Abstract

The new family of unconventional iron-based superconductors discovered in 2006 immediately relieved their copper-based high-temperature predecessors as the most actively studied superconducting compounds in the world. The experimental and theoretical effort made in order to unravel the mechanism of superconductivity in these materials has been overwhelming. Although our understanding of their microscopic properties has been improving steadily, the pairing mechanism giving rise to superconducting transition temperatures up to 55 K remains elusive. And yet the hope is strong that these materials, which possess a drastically different electronic structure but similarly high transition temperatures compared to the copper-based compounds, will shed essential new light onto the several-decade-old problem of unconventional superconductivity. In this work we review the current understanding of the itinerant-charge-carrier dynamics in the iron-based superconductors and parent compounds largely based on the optical conductivity data the community has gleaned over the past seven years using such experimental techniques as reflectivity, ellipsometry, and terahertz transmission measurements and analyze the implications of these studies for the microscopic properties of the iron-based materials as well as the mechanism of superconductivity therein.

Ab-initio investigation of the electronic structure in the superconducting EuFe2(As1−xPx)2

“…So, we confirm that the Fe 3d-electrons dominate the density of states near the Fermi level; this indicates that these electrons could be the origin of superconductivity in these materials. Several ab initio calculations [24][25][26][27][28][29] have shown that the electronic structure of many similar materials have a significant contribution of Fe 3d-electrons near the Fermi level, which are in excellent agreement with our results.…”

Correlation-driven metal-insulator transition in proximity to an iron-based superconductor

“…Figure 4(i) shows the comparison of the calculated (x = 0) and measured (x = 0.02) optical conductivity in metallic NaFe 1−x Cu x As. Theory reproduces all of the main spectral features: the characteristic for iron pnictides strong and incoherent itinerant response [40]; absorption band centered near 0.5 eV and modified from the DFT value by a typical bandwidth renormalization factor of 2-3 (Ref. [48]); higher-energy interband transitions.…”

“…2(d)] is gradually suppressed in the x = 0.18 and x = 0.30 compounds and entirely eliminated at x = 0.44 and x = 0.48 substitution due to the opening of an excitation gap in the electronic band structure. However, it is evident that the copper substitution likewise strongly affects the ubiquitous in iron pnictides 0.5 eV absorption band [40], which stems from transitions between Fe-3d states [38]. This band shifts to higher energies and shapes an absorption edge in the insulating NaFe 1−x Cu x As indicating that the DOS up to about 1 eV experiences substantial suppression.…”

Phase stability and large in-plane resistivity anisotropy in the 112-type iron-based superconductor Ca1−xLaxFeAs2

“…The discovery of high temperature superconductivity in the iron based materials [1] triggered a large number of investigations [2][3][4][5]. The basic ingredient of this class of materials is square nets of iron tetrahedrally coordinated by a pnictide or a chalcogenide.…”