International Journal of Modern Physics B

Memory function formalism or projection operator technique is an extremely useful method to study the transport and optical properties of various condensed matter systems. A recent revival of its uses in various correlated electronic systems is being observed. It is being used and discussed in various contexts, ranging from nonequilibrium dynamics to the optical properties of various strongly correlated systems such as high temperature superconductors. However, a detailed discussion on this method, starting from its origin to its present day applications at one place is lacking. In this paper, we attempt a comprehensive review of the memory function approach focusing on its uses in studying the dynamics and the transport properties of correlated electronic systems.

In this paper, we analyzed the ability of Lielmezs–Herrick (LH) correlation for the temperature-dependent surface tension of 28 hydrocarbons. We found that compared with other published correlations, the original LH correlation stands well only for four fluids. By using new data in REFPROP database, we refitted the two parameters of LH correlation. Two sets values are obtained. One is the updated corresponding state LH correlation, which is fluid independent. The other is the two-parameter LH correlation, which is fluid dependent. We found that the former clearly improves the accuracy of the original LH correlation and the latter is the best among all of the correlations we know.

Reflection statistics have not been well studied for optical random media whose mean refractive indices do not match with the refractive indices of their surrounding media. Here, we theoretically study how this refractive index mismatch between a one-dimensional (1D) optical sample and its surrounding medium affects the reflection statistics in the weak disorder limit, when the fluctuation part of the refractive index $(\mathrm{\Delta }n)$ is much smaller than the mismatch as well as the mean refractive index of the sample $(\mathrm{\Delta }n\ll 〈n〉)$. In the theoretical derivation, we perform a detailed calculation that results in the analytical forms of the mean and standard deviation (STD) of the reflection coefficient in terms of disorder parameters $({〈{(\mathrm{\Delta }n)}^2〉}^{\frac{1}{2}}$ and its correlation length $l_c)$ in an index mismatched backscattering system. Particularly, the orders of disorder parameters in STD of the reflection coefficient for index mismatched systems are shown to be lower $(\sim {(〈\mathrm{\Delta }{n}^2〉l_c)}^{1/2})$ than that of the matched systems $(\sim 〈\mathrm{\Delta }{n}^2〉l_c)$. By comparing STDs of the reflection coefficient values of index matched and mismatched systems, we show that reflection coefficient at the sample boundaries in index mismatched systems can enhance the signal of the STD to the “disorder parameters” of the reflection coefficient. In terms of biophotonics applications, this result can lead to potential techniques that effectively extract the sample disorder parameters by manipulating the index mismatched conditions. Potential applications of the technique for enhancement in sensitivity of cancer detection at the single cell level are also discussed.

The effect of La on the diffusion of Nb in fcc Fe has been investigated using the first-principles calculations based on the density functional theory. The binding energies of Nb–vacancy, La–vacancy and La–Nb pairs have been calculated. The interactions of Nb–vacancy and La–Nb are attractive in 1nn and 2nn configurations (nn: nearest–neighbor). La atom attracts strongly with the 1nn vacancy, but has a weakly repulsive interaction with the 2nn vacancy. We consider four different Nb jumps in the presence of La atom to investigate the Nb diffusion in terms of vacancy formation and migration energy. The results suggest that La increases the diffusion activation energy of Nb in fcc Fe matrix, and is helpful to decelerate the Nb-diffusion-involved phase transformation process.

Magnetic properties of the half-filled Hubbard model on the honeycomb lattice, which is a simple model of graphene, are studied using the variational cluster approximation (VCA). We found that the critical interaction strength of a magnetic transition is slightly lower than that of the nonmagnetic metal-to-insulator transition and the magnetic order parameter is already nonnegligible at the latter transition point. Thus, a semi-metallic state becomes a magnetic insulator as the interaction strength increases, and a spin liquid state characterized by a Mott insulator without spontaneously broken spatial or spin symmetry, or a state very close to that is not realized in this system. Both the magnetic and nonmagnetic metal-to-insulator transitions are of the second-order. Our results agree with recent large scale quantum Monte Carlo (QMC) simulations.

In the present study, pure and ${}_{\mathrm{\text{L}}}$-cystine (LC) doped zinc thiourea sulphate (ZTS) crystals have been grown by slow evaporation solution technique at ambient temperature. The powder X-ray diffraction (XRD) analysis has been carried out to identify the shifts in peak positions and structural parameters of grown crystals. The incorporation of LC in ZTS crystal has been qualitatively analyzed by means of Fourier transform infrared (FTIR) spectroscopic study. In UV-visible studies, the influence of LC on optical transparency, bandgap and various optical constants of ZTS crystal have been investigated to explore various optical applications. The thermal stability of LC doped ZTS crystal has been determined by means of differential scanning calorimetry (DSC) analysis. The hardness behavior and hardness number of grown crystals have been comparatively evaluated by employing the Vicker’s microhardness test. The dielectric study of pure and LC doped ZTS crystal has been carried out at different temperature. In Kurtz–Perry powder technique, the second harmonic generation (SHG) efficiency of LC doped ZTS crystal is found to be 1.16 times that of ZTS crystal.

In this study, we employed Wu–Cohen generalized gradient approximation (WC-GGA) to calculate the structural stability, whereas the modified Becke and Johnson local-density approximation (mBJLDA) functional has been used to determine the electronic and magnetic properties of ${\mathrm{\text{Zn}}}_{1-x}{\mathrm{\text{TM}}}_x\mathrm{\text{Te}}$ $(\mathrm{\text{TM}}=\mathrm{\text{Fe, Co, Ni}})$ alloys in the $x$ range 0–1. Structural optimization in paramagnetic (PM), ferromagnetic (FM) and anti-ferromagnetic (AFM) orders has been done to check the state stability of the doped alloys and then verified with the calculated values of enthalpy of formation $(\mathrm{\Delta }H)$. The erections of enthalpies were negative which gave the evidence of structural stability in FM phase for all three alloys. Our calculated values of equilibrium lattice constants decreased by increasing the TM concentration, in ${\mathrm{\text{Zn}}}_{1-x}{\mathrm{\text{TM}}}_x\mathrm{\text{Te}}$ $(\mathrm{\text{TM}}=\mathrm{\text{Fe, Co, Ni}})$ alloys. We found ferromagnetism caused by the spin polarization of electron in TM-$d$ states in the studied alloys by analyzing the calculated band structure (BS), density of state (DOS) and magnetic moments. The calculated ferromagnetism was also explained from the Zener model. Due to the tetrahedral crystal field, the $3d$-state of TM splits into double $e_g$ and triple degenerate $t_{2g}$ states and our calculated results show the strong pd interaction is only due to $t_{2g}$. Furthermore, we predict exchange splitting energies ${\mathrm{\Delta }}_x(d)$ and ${\mathrm{\Delta }}_x(pd)$ and exchange constants $(N_0\alpha )$ and $(N_0\beta )$. Their calculated values are consistent with typical magneto-optical experiment. The magnetic moments of TM ions were reduced by increasing TM concentration in ${\mathrm{\text{Zn}}}_{1-x}{\mathrm{\text{TM}}}_x\mathrm{\text{Te}}$ $(\mathrm{\text{TM}}=\mathrm{\text{Fe, Co, Ni}})$ alloys, while trivial local magnetic moments at Zn and Te sites were also found.

Fuel cell is undoubtedly widespread energy conversion technology, which can convert fuel (biogas) energy into electricity. Solid oxide fuel cell (SOFC) is one of the best choices among the fuel cell’s family due to high efficiency and fuel flexibility. In this study, zinc-based nanostructured ${\mathrm{\text{Mn}}}_{0.20}{\mathrm{\text{Fe}}}_x{\mathrm{\text{Zn}}}_{0.80-x}{\mathrm{\text{O}}}_{\delta }$ electrode materials were successfully developed by solid state reaction. The proposed materials have been characterized by XRD and SEM. The electrical conductivities have been examined by four-probe DC method in the temperature range of 300–600${}^{\circ }$C, the maximum values were recorded and found to be 12.019 and 5.106 S/cm at natural gas and air atmosphere, respectively. The electrochemical performance has been measured employing NK-SDC electrolyte material and their current density versus voltage and current density versus power density (I-V and I-P characteristics) have been drawn. The maximum power density was found to be 170 mW/cm² using natural gas as a bio-fuel over a temperature of 600${}^{\circ }$C.

Two alternating homogeneous materials are periodically introduced along the radial direction, forming a circular plate of radial phononic crystal (CPRPC). To illustrate the characteristics of the out-of-plane transverse wave and the in-plane longitudinal wave propagating along the radial direction, the transfer matrices are derived based on the basic wave equations of a thin circular plate in cylindrical coordinates. Localization factors are introduced to evaluate the average attenuation of the transverse and longitudinal waves in the structure, and corresponding bandgaps are obtained. Moreover, finite element method simulations, numerical analyses and the insertion loss method are combined to investigate the effects of the main parameters on these wave bandgaps. The results show that significant transverse and longitudinal wave bandgaps caused by the radial periodicity of the CPRPC exist, and the structural and material parameters have essential influences on them.

In order to understand the role of superconductivity in superconducting transmission line resonator, we derive the mode equations using the macroscopic wavefunction of the Cooper pairs. We make an appropriate scaling to obtain the dimensionless form of equations and establish the validity of good conductor approximation under most circumstances. Quantization of superconducting transmission line resonator is realized by the black-box principle. We also briefly discuss that the deviation from good conductor behavior would result in the observable effects, such as the considerable decrease of phase velocity and the soliton.