Direct observation of a Fermi liquid-like normal state in an iron-pnictide superconductor.

Alona Tytarenko,Anne De Visser,Steve Johnston,Yingkai Huang,Erik Van Heumen

doi:10.1038/srep12421

Alona Tytarenko, Anne De Visser + Show 3 more

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https://doi.org/10.1038/srep12421

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Abstract

There are two prerequisites for understanding high-temperature (high-Tc) superconductivity: identifying the pairing interaction and obtaining a correct description of the normal state from which superconductivity emerges. The nature of the normal state of iron-pnictide superconductors, and the role played by correlations arising from partially screened interactions, are still under debate. Here we show that the normal state of carefully annealed electron-doped BaFe2−xCoxAs2 at low temperatures has all the hallmark properties of a local Fermi liquid, with a more incoherent state emerging at elevated temperatures, an identification made possible using bulk-sensitive optical spectroscopy with high frequency and temperature resolution. The frequency dependent scattering rate extracted from the optical conductivity deviates from the expected scaling M2 (ω, T) ∝ ()2 + (pπkBT)2 with p ≈ 1.47 rather than p = 2, indicative of the presence of residual elastic resonant scattering. Excellent agreement between the experimental results and theoretical modeling allows us to extract the characteristic Fermi liquid scale T0 ≈ 1700 K. Our results show that the electron-doped iron-pnictides should be regarded as weakly correlated Fermi liquids with a weak mass enhancement resulting from residual electron-electron scattering from thermally excited quasi-particles.

Highlights

There are two prerequisites for understanding high-temperature superconductivity: identifying the pairing interaction and obtaining a correct description of the normal state from which superconductivity emerges
Strong electronic correlations and Mott physics have played an important role in shaping our understanding of high-Tc superconductivity (HTSC)[1]
Unlike the cuprate HTSC, the pnictides are properly classified as moderately correlated semi-metals[3]

Summary

Introduction

There are two prerequisites for understanding high-temperature (high-Tc) superconductivity: identifying the pairing interaction and obtaining a correct description of the normal state from which superconductivity emerges. Unlike the cuprate HTSC, the pnictides are properly classified as moderately correlated semi-metals[3] By studying their normal state properties a new picture has started to emerge[4] where intra-atomic exchange processes (Hund’s coupling) govern the degree of correlation effects. Werner et al showed[8] that the combined effect of dynamic screening (manifested through a single particle self-energy, Σ (ω, T)) and orbital occupancy results in a Fermi-liquid like state in electron-doped pnictides, while a spin-freezing transition separates an incoherent metal regime from the FL regime in hole-doped materials For a simple Drude metal M (ω, T) = iΓ D is frequency independent, while interactions beyond simple impurity scattering introduce a frequency and temperature dependence The single particle self-energy Σ (ω, T) manifests itself in the free charge carrier response, appearing as a deviation from a classical Drude response

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