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The magnetically driven metal-insulator transition (MIT) was predicted by Slater in the fifties. Here a long-range antiferromagnetic (AF) order can open up a gap at the Brillouin electronic band boundary regardless of the Coulomb repulsion magnitude. However, while many low-dimensional organic conductors display evidence for an AF driven MIT, in three-dimensional (3D) systems the Slater MIT still remains elusive. We employ terahertz and infrared spectroscopy to investigate the MIT in the NaOsO3 3D antiferromagnet. From the optical conductivity analysis we find evidence for a continuous opening of the energy gap, whose temperature dependence can be well described in terms of a second order phase transition. The comparison between the experimental Drude spectral weight and the one calculated through Local Density Approximation (LDA) shows that electronic correlations play a limited role in the MIT. All the experimental evidence demonstrates that NaOsO3 is the first known 3D Slater insulator. [ABSTRACT FROM AUTHOR]

The magnetically driven metal-insulator transition (MIT) was predicted by Slater in the fifties. Here a long-range antiferromagnetic (AF) order can open up a gap at the Brillouin electronic band boundary regardless of the Coulomb repulsion magnitude. However, while many low-dimensional organic conductors display evidence for an AF driven MIT, in three-dimensional (3D) systems the Slater MIT still remains elusive. We employ terahertz and infrared spectroscopy to investigate the MIT in the NaOsO3 3D antiferromagnet. From the optical conductivity analysis we find evidence for a continuous opening of the energy gap, whose temperature dependence can be well described in terms of a second order phase transition. The comparison between the experimental Drude spectral weight and the one calculated through Local Density Approximation (LDA) shows that electronic correlations play a limited role in the MIT. All the experimental evidence demonstrates that NaOsO3 is the first known 3D Slater insulator. [ABSTRACT FROM AUTHOR]

The ab-plane optical conductivity of seven single crystals, belonging to the family BiSrLaCuO, has been measured for hole concentrations per Cu site 0.03≤ p≤0.18, and for 6 K≤ T≤300 K (500 K for p=0.16). At low doping, ten phonon lines are detected, which are due to the removal of the degeneracy of five E modes (out of the predicted six). They are superimposed to a far-infrared band, which as doping increases, closes the insulating gap thus building up the Drude term. The insulator-to-metal transition occurs between p=0.7 and p=0.10 consistently with a Mott mechanism. In the metallic phase, a multiband analysis identifies a Drude term plus a mid-infrared band, which weakly depends on temperature and softens as p increases, like in other cuprates. The optical response of the crystal at optimum doping has been analyzed also in the superconducting phase. The Ferrel-Glover-Tinkham sum rule requires an integration up to Ω≫6 Δ and the penetration depth is 290 nm. The bosonic spectral function includes a strong peak around 50 meV, which survives up to 500 K and, therefore, might be assigned to an electron-phonon interaction. [ABSTRACT FROM AUTHOR]

Abstract: We report on the fabrication and systematic characterization of nanoantenna arrays with several different geometries realized both on standard silicon (Si) substrates and Calcium Fluoride (CaF2) substrates aimed at the realization of a mid-Infrared protein detector. In particular, we present a novel nanofabrication procedure which allows the adoption of CaF2 in a standard lithographic process with results comparable to the ones obtained on silicon wafers. The transmittance and reflectance spectra of the nanoantennas, were acquired by means of an Infrared microscope coupled to a Michelson Interferometer. In all the nanoantenna devices, the plasmonic resonance follows a linear scaling relation: a lattice parameter change of a ±(5–10)%, indeed, results in a shift of the Si (1,0) plasmonic resonance frequency which is proportional to 1/a. This scaling behavior offers a useful tool for device frequency tuning, which can be used to obtain a fine spectral overlap with the protein amide-I and amide-II bands. A Lorentzian analysis of the resonance peaks reveals that our nanostructures have an high Q factor (Q =ν0/Δν), demonstrating the effectiveness of our fabrication procedures. [Copyright &y& Elsevier]

The ab-plane optical conductivity of 11 single crystals, belonging to the families Sr2-xCuO2Cl2, Y1-xCaxBa2Cu3O6, Bi2Sr2-xLaxCuO6 and Bi2Sr2CaCu2O8, has been measured with hole concentrations p between 0 and 0.18 and for 6K ⩽ T ⩽ 500K to obtain an infrared picture of the p, T phase diagram of the Cu-O plane. At extreme dilution (p = 0.005), a narrow peak is observed at 1570 cm-1 (195 meV), which we assign to a single-hole bound state. For increasing doping, that peak broadens into a far-infrared (FIR) band whose low-energy edge sets the insulating gap. The insulator-to-metal transition (IMT) occurs when the softening of the FIR band closes the gap, thus evolving into a Drude term. In the metallic phase, a multi-band analysis identifies a mid-infrared band which weakly depends on temperature and softens for increasing p, while the extended-Drude analysis leads to an optical scattering rate larger than the frequency, as was found in other cuprates. The infrared spectral weight W(T ) is consistent with a Fermi liquid renormalized by strong correlations, provided that the T 4 term of the Sommerfeld expansion is included above 300 K. In the superconducting phase, the optical response of single-layer Bi2Sr2-xLaxCuO6 at optimum doping is similar to that of the corresponding optimally doped bilayer Bi2Sr2CaCu2O8. [ABSTRACT FROM AUTHOR]

Vanadium sesquioxide V2O3 is considered a textbook example of Mott-Hubbard physics. In this paper, we present an extended optical study of its whole temperature/doping phase diagram as obtained by doping the pure material with M=Cr or Ti atoms (V1-xMx)2O3. We reveal that its thermodynamically stable metallic and insulating phases, although macroscopically equivalent, show very different low-energy electrodynamics. The Cr and Ti doping drastically change both the antiferromagnetic gap and the paramagnetic metallic properties. A slight chromium content induces a mesoscopic electronic phase separation, while the pure compound is characterized by short-lived quasiparticles at high temperature. This study thus provides a new comprehensive scenario of the Mott-Hubbard physics in the prototype compound V2O3. [ABSTRACT FROM AUTHOR]

The magnetically driven metal-insulator transition (MIT) was predicted by Slater in the fifties. Here a long-range antiferromagnetic (AF) order can open up a gap at the Brillouin electronic band boundary regardless of the Coulomb repulsion magnitude. However, while many low-dimensional organic conductors display evidence for an AF driven MIT, in three-dimensional (3D) systems the Slater MIT still remains elusive. We employ terahertz and infrared spectroscopy to investigate the MIT in the NaOsO3 3D antiferromagnet. From the optical conductivity analysis we find evidence for a continuous opening of the energy gap, whose temperature dependence can be well described in terms of a second order phase transition. The comparison between the experimental Drude spectral weight and the one calculated through Local Density Approximation (LDA) shows that electronic correlations play a limited role in the MIT. All the experimental evidence demonstrates that NaOsO3 is the first known 3D Slater insulator. [ABSTRACT FROM AUTHOR]