Analysis Of Optical Conductivity Research Articles

First-principles calculations to investigate the structural, electronic, optical, mechanical, and thermodynamic properties of double perovskites Ba2WB′O6 (B′ = Co, Fe, Mn, Ni, and Zn)

We utilized the WIEN2K code within the DFT framework to comprehensively investigate Ba2WBˈO6 (Bˈ = Mn, Fe, Co, Ni, Zn) double perovskite compounds. Structural stability, assessed by Goldsmith's tolerance factor (tG), revealed values close to unity, indicative of stable cubic perovskite structures. The Birch-Murnaghan's equation of state optimization determined ground states, unveiling trends in lattice constant (a0) and bulk modulus (B) for different cations. Structural and phonon stability were confirmed by negative energy formation and real frequencies in phonon calculations. DFPT results affirmed the thermodynamic stability of all compounds. Electronic band structure calculations identified Ba2WMnO6 and Ba2WNiO6 as conductors, while Ba2WCoO6 and Ba2WZnO6 were insulators with 3.7 eV and 3.8 eV band gaps, respectively. Ba2WFeO6 demonstrated semiconducting properties with a 2.37 eV band gap. Density of States (DOS) analysis supported the electronic band structure. Optical conductivity analysis revealed increasing values at higher energy ranges, followed by gradual decreases, differing between conductors and insulators. Absorption coefficient indicated potential suitability for optoelectronic devices, and refractive index analysis highlighted trends in material transparency. To understand fundamental properties, thermodynamic characteristics (thermal expansion coefficient, heat capacities, Debye temperature) were analyzed across a wide pressure (0–30 GPa) and temperature (0–1600 K) range.

Optical Conductivity Analysis of Green CuO Nanoparticles Using Plant Leaf Extract

The optical properties of green synthesized CuO nanoparticles such as absorption coefficient, refractive index, band gap, dielectric constant and optical conductivity were analyzed. XRD shows that upon temperature treatment of green CuO nanoparticles, the crystal size increases and thus the crystallinity increases due to the decrease in the number of crystals per unit area. Due to the high crystallinity, the absorption coefficient exhibits a high electronic shift and the refractive index exhibits good polarization of the ions. Thus the dielectric constant of the real and imaginary regions decreases as the photon energy increases. Higher temperatures exhibit higher photon energy levels. Optical conductivity has induced electron annihilation due to the absorption coefficient of increased photo energy light; Hence the optical conductivity analysis of Lantana camara capped CuO nanoparticles indicated the stability of electrical conductivity with increase in photo power.

Kollektivnye i kvazilokal'nye mody v opticheskikh spektrakh geksaboridov YB6 i YbB6 s yan-tellerovskoy strukturnoy neustoychivost'yu

The broad-band reflection spectra of YB6 and YbB6 hexaborides with Jahn–Teller instability of the boron cage have been measured at room temperature. An optical conductivity analysis has revealed, along with the Drude electronic components, heavily overdamped collective modes, which are notable in YB6 for high dielectric contributions, Δε = 2000–5700. The fraction of nonequilibrium charge carriers in YB6, which is at the boundary of structural instability in the hexaboride family, reaches 85–90%, whereas this fraction in doped YbB6 semiconductor is not higher than 25%. It has been shown that unlike the predictions of the topological Kondo insulator model, the surface “metallization” in Yb2+B6 crystals can be explained by additional doping of a surface layer with Yb3+ ions.

On the energy scale involved in the metal to insulator transition of quadruple perovskite EuCu3Fe4O12: infrared spectroscopy and ab-initio calculations.

Optical measurements were carried out by infrared spectroscopy on AA′3B4O12 A-site ordered quadruple perovskite EuCu3Fe4O12 (microscopic sample) as function of temperature. At 240 K (=TMI), EuCu3Fe4O12 undergoes a very abrupt metal to insulator transition, a paramagnetic to antiferromagnetic transition and an isostructural transformation with an abrupt large volume expansion. Above TMI, optical conductivity reveals a bad metal behavior and below TMI, an insulating phase with an optical gap of 125 meV is observed. As temperature is decreased, a large and abrupt spectral weight transfer toward an energy scale larger than 1 eV is detected. Concurrently, electronic structure calculations for both high and low temperature phases were compared to the optical conductivity results giving a precise pattern of the transition. Density of states and computed optical conductivity analysis identified Cu3dxy, Fe3d and O2p orbitals as principal actors of the spectral weight transfer. The present work constitutes a first step to shed light on EuCu3Fe4O12 electronic properties with optical measurements and ab-initio calculations.

Insulating nature ofNa2IrO3: Mott-type or Slater-type

We have investigated temperature-dependent electronic structures of Na2IrO3 to unravel its insulating nature. Employing the combined scheme of the density-functional theory (DFT) and the dynamical mean-field theory (DMFT), we have shown that the insulating state persists even above the Neel temperature (T_{N}), which reveals that Na2IrO3 is classified into a Mott-type insulator. The measured photoemission spectrum in the paramagnetic (PM) state is well described by the electronic structure obtained from the DFT+DMFT for the insulating state above T_{N}. The analysis of optical conductivity, however, suggests that the non-local correlation effect is also important in Na2IrO3. Therefore, Na2IrO3 is not to be a standard Mott insulator in that the extended nature and the non-local correlation effect of Ir 5d electrons are important as well in describing its electronic and magnetic properties.

Absorption and optical conduction in InSe/ZnSe/InSe thin film transistors

In this work, (n)InSe/(p)ZnSe and (n)InSe/(p)ZnSe/(n)InSe heterojunction thin film transistor (TFT) devices are produced by the thermal evaporation technique. They are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy and optical spectroscopy techniques. While the InSe films are found to be amorphous, the ZnSe and InSe/ZnSe films exhibited polycrystalline nature of crystallization. The optical analysis has shown that these devices exhibit a conduction band offsets of 0.47 and valence band offsets of 0.67 and 0.74[Formula: see text]eV, respectively. In addition, while the dielectric spectra of the InSe and ZnSe displayed resonance peaks at 416 and 528[Formula: see text]THz, the dielectric spectra of InSe/ZnSe and InSe/ZnSe/InSe layers indicated two additional peaks at 305 and 350[Formula: see text]THz, respectively. On the other hand, the optical conductivity analysis and modeling in the light of free carrier absorption theory reflected low values of drift mobilities associated with incident alternating electric fields at terahertz frequencies. The drift mobility of the charge carrier particles at femtoseconds scattering times increased as a result of the ZnSe sandwiching between two InSe layers. The valence band offsets, the dielectric resonance at 305 and 350[Formula: see text]THz and the optical conductivity values nominate TFT devices for use in optoelectronics.

Room temperature ferromagnetic properties of epitaxial (111) Y0.225Sr0.775CoO3−δ thin film grown on single crystalline (111) MgO substrate

Epitaxial (111) Y0.225Sr0.775CoO3−δ (YSCO) thin films were deposited on single crystalline (111) MgO substrates by a pulsed laser deposition method. The YSCO thin film exhibited room temperature ferromagnetism with a remanent magnetization of 1.5×10−5emu. The magnetic force microscopy (MFM) study revealed that the YSCO thin film had a mosaic MFM domain structure. The comparison of domain wall energy for the YSCO and PZT indicates that the large domain wall energy induce the large domain size, though the large magnetization value reduce the magnetic domain size in the case of Co. According to the optical conductivity analysis by spectroscopic ellipsometry, it is inferred that the transition from the intermediate spin state to the high spin state of the YSCO thin film is attributed to the ferromagnetism of the Co4+ ion.

Excitonic correlation in the Mott crossover regime in Ge

Exciton Mott transition (EMT) in Ge was investigated by using optical-pump and terahertz-probe spectroscopy. From the quantitative analysis of optical conductivity and dielectric function, we evaluated the densities of unbound electron-hole pairs and excitons after the photoexcitation, from which we determined the ionization ratio of excitons \ensuremath{\alpha}. The Mott crossover density region in Ge was elucidated from the density dependence of \ensuremath{\alpha} in the temperature range above the critical temperature of electron-hole droplets. The $1s\ensuremath{-}2p$ excitonic transition energy hardly shifted with increasing density toward the EMT. Combined with the similar results recently observed in bulk Si, we suggest that the robustness of excitonic correlation against the Coulomb screening is a universal feature in bulk semiconductors in the Mott crossover regime.

Infrared evidence of a Slater metal-insulator transition in NaOsO3

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.

Incoherent midinfrared charge excitation and the high-energy anomaly in the photoemission spectra of cuprates

On the basis of a semiphenomenological model, it is argued that the high-energy anomaly observed in recent photoemission experiments on cuprates is caused by interaction with an overdamped bosonic mode in the midinfrared region of the spectrum. Analysis of optical conductivity allows us to connect this excitation to the incoherent charge response reported for the majority of high-${T}_{c}$ materials and some other perovskites. We show that its large damping is an essential feature responsible for the ``waterfall'' dispersion and linewidth of the spectral weight.

Optical investigation of the electronic structures ofY2Ru2O7,CaRuO3,SrRuO3,andBi2Ru2O7

We investigated the electronic structures of the bandwidth-controlled ruthenates, Y$_{2}$Ru$_{2}$O$_{7}$, CaRuO$_{3}$, SrRuO$_{3}$, and Bi$_{2}$Ru$% _{2}$O$_{7}$, by optical conductivity analysis in a wide energy region of 5 meV $\sim $ 12 eV. We could assign optical transitions from the systematic changes of the spectra and by comparison with the O 1$s$ x-ray absorption data. We estimated some physical parameters, such as the on-site Coulomb repulsion energy and the crystal-field splitting energy. These parameters show that the 4$d$ orbitals should be more extended than 3$d$ ones. These results are also discussed in terms of the Mott-Hubbard model.

Optical investigation of the electronic structures of Y2Ru2O7, CaRuO3, SrRuO3, and Bi2Ru2O7

We investigated the electronic structures of the bandwidth-controlled ruthenates. Y 2 Ru 2 O 7 , CaRuO 3 . SrRuO 3 , and Bi 2 Ru 2 O 7 , by optical conductivity analysis in a wide energy region of 5 meV-12 eV. We could assign optical transitions from the systematic changes of the spectra and by comparison with the O 1s x-ray absorption data. We estimated some physical parameters, such as the on-site Coulomb repulsion energy and the crystal-field splitting energy. These parameters show that the 4d orbitals should be more extended than 3d ones. These results are also discussed in terms of the Mott-Hubbard model.