Optical properties of $A$Fe${}_2$As${}_2$ ($A=$Ca, Sr, and Ba) single crystals

Abstract

The detailed optical properties have been determined for the iron-based materials $A$Fe${}_2$As${}_2$, where $A=$Ca, Sr, and Ba, for light polarized in the iron-arsenic ($a-b$) planes over a wide frequency range, above and below the magnetic and structural transitions at $T_N=$ 172, 195, and 138 K, respectively. The real and imaginary parts of the complex conductivity are fit simultaneously using two Drude terms in combination with a series of oscillators. Above $T_N$, the free-carrier response consists of a weak, narrow Drude term, and a strong, broad Drude term, both of which show only a weak temperature dependence. Below $T_N$ there is a slight decrease of the plasma frequency but a dramatic drop in the scattering rate for the narrow Drude term, and for the broad Drude term there is a significant decrease in the plasma frequency, while the decrease in the scattering rate, albeit significant, is not as severe. The small values observed for the scattering rates for the narrow Drude term for $T\ll T_N$ may be related to the Dirac cone-like dispersion of the electronic bands. Below $T_N$ new features emerge in the optical conductivity that are associated with the reconstruction Fermi surface and the gapping of bands at ${\Delta }_1\simeq$ 45 $-$ 80 meV, and ${\Delta }_2\simeq$ 110 $-$ 210 meV. The reduction in the spectral weight associated with the free carriers is captured by the gap structure, specifically, the spectral weight from the narrow Drude term appears to be transferred into the low-energy gap feature, while the missing weight from the broad term shifts to the high-energy gap.

11 pages, 4 figures and 2 tables; 6 pages of supplemental material. Revisions conform with published version

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Cited by in corpus (13)

• Origin of the Charge Density Wave in the Kagome Metal CsV${}_3$Sb${}_5$ as Revealed by Optical Spectroscopy
• Temperature-induced band shift in ferromagnetic Weyl semimetal Co3Sn2S2
• Two-dimensional Massless Dirac Fermions in Antiferromagnetic AFe2As2 (A = Ba, Sr)
• Optical study of Dirac fermions and related phonon anomalies in antiferromagnetic compound CaFeAsF
• Muon spin rotation and infrared spectroscopy study of $B{a}_{1-x}N{a}_{x}F{e}_{2}A{s}_2$
• Constraints on the total coupling strength to bosons in iron based superconductors
• Optical and photoemission investigation of structural and magnetic transitions in the iron-based superconductor Sr${}_{0.67}$Na${}_{0.33}$Fe${}_2$As${}_2$
• Pseudogap and Strong Pairing Induced by Incipient and Shallow Bands in the Quasi-Two-Dimensional KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Unravelling the mechanism of the semiconducting-like behavior and its relation to superconductivity in (CaFe${}_{1-x}$Pt${}_x$As)${}_{10}$Pt${}_3$As${}_8$
• Vibrational anomalies in AFe${}_2$As${}_2$ (A$=$Ca, Sr, and Ba) single crystals
• Anisotropic optical properties of detwinned BaFe${}_2$As${}_2$
• Linear scaling relation between two-dimensional massless Dirac fermion Fermi velocity and Fe-As bond length in iron arsenide superconductor systems
• Evolution of charge dynamics in FeSe${}_{1-x}$Te${}_x$: Effects of electronic correlations and nematicity