Structural electronic and vibrational properties analysis of Li2CaX (X = Sn, Pb) heusler alloys: a comparative study

This study was focused on structural, electronic and vibrational properties of Li _2 CaSn and Li _2 CaPb with density functional theory. All properties of these compounds were computed by implementing General Gradient Approximation and using Quantum Espresso software programme. As a result of the calculations, it was found that the lattice parameter is 6.967 Å and bulk modulus is 33.94 GPa for Li _2 CaSn. Also, these values are 7.062 Å and 29.574 GPa for Li _2 CaPb. The calculated lattice parameters are in good agreement with the available experimental data. There is no previous theoretical calculation for Li _2 CaSn and Li _2 CaPb compounds. It was calculated that Li _2 CaSn and Li _2 CaPb have a semi-metal property. The full phonon dispersion curves of Li _2 CaSn and Li _2 CaPb compounds in the Heusler type structure were examined using the linear response method. Under 0 kbar pressure, Li _2 CaPb was unstable while Li _2 CaSn was dynamically stable. Calculations showed that when 38.42 kbar pressure is applied to the Li _2 CaPb compound, the Li _2 CaPb compound becomes dynamically stable. It is believed that this study will shape future studies

The effect of disorder on local electron temperature in quantum Hall systems

The local electron temperature distribution is calculated considering a two dimensional electron system in the integer quantum Hall regime in presence of disorder and uniform perpendicular magnetic fields. We solve thermo-hydrodynamic equations to obtain the spatial distribution of the local electron temperature in the linear-response regime. It is observed that, the variations of electron temperature exhibit an antisymmetry regarding the center of the sample in accordance with the location of incompressible strips. To understand the effect of sample mobility on the local electron temperature we impose a disorder potential calculated within the screening theory. Here, long range potential fluctuations are assumed to simulate cumulative disorder potential depending on the impurity atoms. We observe that the local electron temperature strongly depends on the number of impurities in narrow samples

The dip effect under integer quantized Hall conditions

In this work we investigate an unusual transport phenomenon observed in two-dimensional electron gas under integer quantum Hall effect conditions. Our calculations are based on the screening theory, using a semi-analytical model. The transport anomalies are dip and overshoot effects, where the Hall resistance decreases (or increases) unexpectedly at the quantized resistance plateaus intervals. We report on our numerical findings of the dip effect in the Hall resistance, considering GaAs/AlGaAs heterostructures in which we investigated the effect under different experimental conditions. We show that, similar to overshoot, the amplitude of the dip effect is strongly influenced by the edge reconstruction due to electrostatics. It is observed that the steep potential variation close to the physical boundaries of the sample results in narrower incompressible strips, hence, the experimental observation of the dip effect is limited by the properties of these current carrying strips. By performing standard Hall resistance measurements on gate defined narrow samples, we demonstrate that the predictions of the screening theory is in well agreement with our experimental findings

First-principles study on electronic, optic, elastic, dynamic and thermodynamic properties of RbH compound

We performed first-principles calculations to obtain the electronic, optical, elastic, lattice-dynamical and thermodynamic properties of RbH compound with rock salt structure. The ground-state properties, i.e., the lattice constant and the band gap were investigated using a plane wave pseudopotential method within density functional theory. The calculated lattice constant, bulk modulus, energy band gap and elastic constants are reported and compared with previous theoretical and experimental results. Our calculated results and the previous results which are obtained from literature are in a good agreement. Moreover, real and imaginary parts of complex dielectric function, reflectivity spectrum, absorption, extinction coefficient and loss function as a function of photon energy and refractive index with respect to photon wavelength were calculated. In addition, temperature dependent thermodynamic properties such as Helmholtz free energy, internal energy, entropy and specific heat have been studied

First-principles study on electronic, optic, elastic, dynamic and thermodynamic properties of RbH compound

We performed first-principles calculations to obtain the electronic, optical, elastic, lattice-dynamical and thermodynamic properties of RbH compound with rock salt structure. The ground-state properties, i.e., the lattice constant and the band gap were investigated using a plane wave pseudopotential method within density functional theory. The calculated lattice constant, bulk modulus, energy band gap and elastic constants are reported and compared with previous theoretical and experimental results. Our calculated results and the previous results which are obtained from literature are in a good agreement. Moreover, real and imaginary parts of complex dielectric function, reflectivity spectrum, absorption, extinction coefficient and loss function as a function of photon energy and refractive index with respect to photon wavelength were calculated. In addition, temperature dependent thermodynamic properties such as Helmholtz free energy, internal energy, entropy and specific heat have been studied