Full-potential Local-orbital Code Research Articles

Effect of Hubbard Potential (U) on Mn Doped BiTeI

In recent years, Bismuth tellurohalide has gained significant attention as a possible candidate for spintronics applications. Among them, BiTeI is one such layered material that shows Rashba spin splitting responsible for transport phenomenon. On the basis of density functional theory calculations using full-potential local-orbital code, we studied the electronic and magnetic properties of Bi2TeMnI2 compound. Our study shows an energy band gap of 1.18 eV for the parent material BiTeI. The main contribution around the Fermi level are from the Bi-6p, I-5p and Te-5p states. Upon doping Mn atom independently to Bi, Te and I site, we found that Te site is energetically most favorable. With Mn doped to Te site, the material is found to transform to ferromagnetic semiconducting state with magnetic easy-axis along [001] with magnetic moment of 3 μB per unit cell. The magnetic moment is found to alter interestingly with the implementation of Hubbard-potential (U). The value first reduces to 1 μB for U = 3 eV and starts changing with increasing value of U. Due to internal ferromagnetic ordering and strong correlation effect, this compound seems to be a promising candidate for spintronics and quantum computing.

Electronic structure, optical properties and defect induced half-metallic ferromagnetism in kagome Cs2Ni3S4

Recent research focuses on electronic structure of kagome materials due to their fascinating properties such as topological insulators, Dirac semimetals, and topological superconductors. Materials with sizable electronic band gap are found to play vital role in device applications. Here, by means of density functional theory calculations, we study the electronic and optical properties of ternary transition metal sulphide Cs2Ni3S4 by using the full potential local orbital code. Standard generalized gradient approximation (GGA) has been employed to consider the electron exchange and correlation effect, and modified Becke–Johnson (mBJ) potential has been used to obtain the accurate band gap of the material. From our electronic structure calculations Cs2Ni3S4 is found to be nonmagnetic semiconductor with an indirect band gap of ∼1.4 eV within GGA + mBJ calculations. The structural analysis demonstrates that Ni atoms form a kagome lattice in a two-dimensional plane, resulting in the presence of a dispersionless flat band located below the Fermi energy. From the optical calculations, analyzing the dielectric function, loss function, and optical conductivity, Cs2Ni3S4 is found to be optically active in the visible as well as lower ultraviolet energy ranges. This suggests that Cs2Ni3S4 may be a suitable candidate for the opto-electronic devices. Additionally, this work may provides a foundation for the development of opto-electronic device and a framework for experimental work. We additionally investigated the effect of vacancy defects in Cs2Ni3S4 to see it’s influence on the electronic and magnetic properties. Interestingly, the Cs-vacancy defect give rise to half-metallic ferromagnetism with an effective magnetic moment of per unit cell.

Electronic and magnetic properties of ternary sulfide Rb2Mn3S4


 
 
 
 Semiconducting materials, especially with a direct band gap, are helpful for modern photovoltaic and optoelectronic device fabrication. Here, based on density functional theory calculations, we predict the electronic and magnetic properties of Rb2Mn3S4 by using the full potential local orbital code. Considering different configurations such as nonmagnetic, ferromagnetic, ferrimagnetic, and antiferromagnetic, the magnetic ground state was found to be ferrimagnetic with the lowest total energy. The calculated effective magnetic moment is 10μBunit cell (two formula units) resulting from the opposite spin interaction between Mn (I) and Mn (II) atoms in Rb2Mn3S4. From our calculations, Rb2Mn3S4 is found to be a semiconductor with a direct energy band gap of 0.75 eV. With the inclusion of the Coulomb interaction (i.e., GGA+U), the band gap is found to rise to 2.34 eV for U = 4 eV.
 
 
 

Tilted Dirac cone gapped due to spin-orbit coupling and transport properties of a 3D metallic system CaIr2Ge2

We present results of electrical transport (resistance, magnetoresistance, Hall effect) and heat capacity measurements performed on single crystals of the tetragonal compound, CaIr2Ge2. Their analysis is supported by the electronic structure data (band dispersion, density of states, Fermi surface), calculated for this three-dimensional (3D) system from first principles, using the full-potential local-orbital code. Interestingly, we have found the highly anisotropic Dirac cone at the Fermi level, in the bulk band structure, being gapped due to the strong p-d hybridization and spin-orbit coupling effects. However, this feature seems to have insignificant influence on the transport properties studied. The compound appears to be metallic-like with a rather low Sommerfeld coefficient (3.23 mJ mol−1 K−2) and non-superconducting even down to 0.1 K. In turn, the transverse magnetoresistance curves do not saturate with magnetic field up to 9 T revealing sub-quadratic scaling but relatively small values (up to 11 % in 2 K) as for Dirac semimetals. We may ascribe these properties to small values of the estimated relaxation time of charge carriers (~10−13 s) and, therefore, small electronic mobilities. Moreover, the angular magnetoresistance exhibits very small anisotropy (~ 1.7 %), in line with weakly anisotropic large 3D Fermi surface sheets, predicted by our calculations.

Electronic structures and superconductivity in LuTE2Si2 phases ([formula omitted]= d-electron transition metal)

In the course of our search for unconventional superconductors amidst the 1:2:2 phases, we have re-investigated the LuTE2Si2 compounds with TE= Fe, Co, Ni, Ru, Pd and Pt. In this paper, we present the results of our fully relativistic ab initio calculations of the band structures, performed using the full-potential local-orbital code. The theoretical data are supplemented by the results of low-temperature electrical transport and specific heat measurements performed down to 0.35K. All the materials studied but LuPt2Si2 crystallize with the body–centered tetragonal ThCr2Si2–type structure (space group I4/mmm). Their Fermi surfaces exhibit a three-dimensional multi–band character. In turn, the Pt–bearing compound adopts the primitive tetragonal CaBe2Ge2–type structure (space group P4/nmm), and its Fermi surface consists of predominantly quasi–two–dimensional sheets. Bulk superconductivity was found only in LuPd2Si2 and LuPt2Si2 (independent of the structure type and dimensionality of the Fermi surface). The key superconducting characteristics indicate a fully-gapped BCS type character. Though the electronic structure of LuFe2Si2 closely resembles that of the unconventional superconductor YFe2Ge2, this Lu–based silicide exhibits neither superconductivity nor spin fluctuations at least down to 0.35K.

Electronic structure of stacking faults in rhombohedral graphite

The electronic structure of stacking faults and surfaces without and with an additional displaced layer is calculated for the case of rhombohedral (ABC) graphite. The full-potential local-orbital code and the generalized gradient approximation to density functional theory are used. All considered surfaces and interfaces induce surface/interface bands. All discovered surface and interface bands are restricted to the vicinity of the symmetry line $K\ensuremath{-}M$ in the two-dimensional Brillouin zone. There are groups of localized band pairs around $\ifmmode\pm\else\textpm\fi{}0$, $\ifmmode\pm\else\textpm\fi{}0.2$, and $\ifmmode\pm\else\textpm\fi{}0.6$ eV for one of the two considered types of stacking faults; $\ifmmode\pm\else\textpm\fi{}0$ and $\ifmmode\pm\else\textpm\fi{}0.5$ eV for the other type and for a displaced surface layer. At the $K$ point in the Brillouin zone, there is a one-to-one correspondence between these localized bands and the eigenvalues of those linear atomic clusters, which are produced by the perturbation of periodicity due to the displaced surface layer or due to the stacking faults. Some of the localized bands produce strong van Hove singularities in the local density of states near the surface or interface at energies up to several 0.1 eV. It is suggested to check these findings experimentally by appropriate spectroscopic methods. Undisturbed bulk (ABC) graphite is virtually a zero-gap semiconductor with a minute density of states at the Fermi energy. Both the surface and any of the considered stacking faults produce sharp peaks in the local density of states near the perturbation at energies of about 10 meV around the Fermi energy. This should provide a considerable contribution to the conductivity and its temperature dependence for samples with stacking faults or large surface-to-volume fraction.