Physical properties of hexagonal BaPtAs with noncentrosymmetric SrPtSb-type and centrosymmetric YPtAs-type crystal structures: Effects of spin-orbit coupling

This is the final version. Available from the American Physical Society via the DOI in this recordRecently, superconductivity in BaPtAs with the noncentrosymmetric SrPtSb and the centrosymmetric YPtAs-structure has been discovered. Its noncentrosymmetric and centrosymmetric structures make BaPtAs a charming compound for searching the effect of spin-orbit coupling (SOC) onto superconductors with broken and preserved spatial inversion symmetry. We have investigated the effect of SOC on the physical and electron-phonon interaction properties of these phases of BaPtAs by using the generalized gradient approximation of the density functional theory and the plane-wave pseudopotential method. The inclusion of SOC has moderate effect on the elastic and electronic properties, and on phonon frequencies for both phases of BaPtAs. However, SOC makes an opposite impact on their Eliashberg spectral function. For the noncentrosymmetric phase, this coupling decreases the strength of dominant peaks of Eliashberg spectral function, reducing the values of average electron-phonon coupling and superconducting transition temperature. The scenario is exactly opposite for the centrosymmetric phase. For both phases, the hybridized Pt-As vibrations play a strongly significant role in determining their electron-phonon interaction properties since their electronic states have the dominant contribution near the Fermi level. The superconducting temperature is estimated to be 2.87 K for the SrPtSb phase and 2.38 K for the YPtAs phase. These values compare well with the reported measured values of 2.8 K and 2.1–3.0 K, respectively

Theoretical investigation of antisymmetric spin-orbit coupling effect on the physical properties of noncentrosymmetric BaPtSb superconductor

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record First principles pseudopotential calculations have been performed to explore the effect of spin-orbit coupling on the electronic, elastic, mechanical, vibrational and electron-phonon interaction properties of noncentrosymmetric BaPtSb crystallizing in the hexagonal SrPtSb-type. This coupling makes only moderate changes to the elastic and mechanical properties but significant changes to the phonon spectrum in the acoustic range. Analysis of the Eliashberg spectral function reveals that these low-frequency phonon modes originate from the vibrations of Pt and Sb atoms and couple strongly to their d and p electronic states at the Fermi level. The spin-orbit coupling has a significant effect on the electron-phonon interaction properties by decreasing the frequencies of some phonon modes and increasing the strength of the most dominant peak of the Eliashberg spectral function. The average electron-phonon coupling increases from 0.617 without spin-orbit coupling to 0.629 with spin-orbit coupling, resulting in the corresponding changes to the superconducting transition temperature from 1.46 to 1.54 K. The latter value of superconducting transition temperature compares very well with its experimental value of 1.64 K

Role of spin-orbit coupling in the physical properties of LaX3 (X=In, P, Bi) superconductors

This is the final version of the article. Available from American Physical Society via the DOI in this record.We report a comprehensive and complementary study on structural, elastic, mechanical, electronic, phonon, and electron-phonon interaction properties of LaX3 (X = In, Pb, and Bi) using first-principles density functional calculations within the local density approximation with and without the spin-orbit coupling (SOC). The calculated lattice parameters for these intermetallic compounds with and without SOC are found to differ by less than 2% from their experimental values. The effect of SOC on the elastic, mechanical, electronic, phonon, and electron-phonon interaction properties is more profound for LaPb3 and LaBi3 containing heavier X elements rather than LaIn3 containing lighter X element. The inclusion of SOC considerably removes the degeneracies of some bands near the Fermi level and makes some phonon branches in LaPb3 and LaBi3 softer and increases the strength of dominant peaks in their Eliashberg spectral functions. Thus the SOC related enhancement of their electron-phonon coupling parameter values can be related to both a softening of their phonon dispersion curves and an increase in their electron-phonon coupling matrix elements. The superconducting transition temperature with SOC is computed to be 0.69 K for LaIn3, 4.23 K for LaPb3, and 6.87 K for LaBi3, which agree very well with the respective measured values of 0.70, 4.18, and 7.30 K

Theoretical investigation of superconductivity mechanism in the filled skutterudites YRu4P12, YOs4P12, LaOs1P12 and LaOs4As12

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record We have searched the structural, electronic, phonon and electron-phonon interaction properties of the filled skutterudites YRu4P12, YOs4P12, LaOs4P12 and LaOs4As12 by utilizing the generalized gradient approximation of the density functional theory. A critical assessment of their electronic density of states (DOS) indicates that the partial DOS of transition metal and pnictogen are considerably present in the energy range below and above the Fermi level but the contribution of the rattling atom (Y or La) to the occupied bands is negligible. The calculated zone-center phonon frequencies of LaOs4As12 compare very well with previous theoretical results. Our electron-phonon calculations suggest that all the studied skutterudites are phonon-mediated conventional superconductors since phonon scattering of electrons plays main role in the transition from the normal state to the superconducting state. A detailed analysis of the Eliashberg spectral function reveals that the contribution of the rattling atom-related vibrations to the electron-phonon interaction properties is moderate. The superconducting critical temperature is found to be 7.73, 2.67, 2.03 and 3.2 for YRu4P12, YOs4P12, LaOs4P12 and LaOs4As12, respectively. These values show a good agreement with their experimentally reported values of 8.5, 2.8, 2.0 and 3.2 K

Theoretical investigation of superconductivity in SrPd2Ge2, SrPd2As2, and CaPd2As2

This is the final version of the article. Available from American Physical Society via the DOI in this record.© 2016 American Physical Society. Ab initio pseudopotential calculations have been performed to investigate the structural, electronic, and vibrational properties of SrPd2Ge2, SrPd2As2, and CaPd2As2 crystallizing in the ThCr2Si2-type body-centered tetragonal structure. Our electronic results show that the density of states at the Fermi level is mainly dominated by the strong hybridization of Pd d states and Ge (or As) p states. The linear response method and the Migdal-Eliashberg approach have been used to calculate the Eliashberg spectral function for all these compounds. By integrating the Eliashberg spectral function, the average electron-phonon coupling parameter (λ) is found to be 0.74 for SrPd2Ge2, 0.66 for SrPd2As2, and 0.72 for CaPd2As2. Using the calculated values of λ and the logarithmically averaged phonon frequency ωln the superconducting critical temperature (Tc) values for SrPd2Ge2, SrPd2As2, and CaPd2As2 are found to be 3.20, 2.05, and 2.48 K, respectively, which are in acceptable agreement with the corresponding experimental values. The relative differences in the Tc values between the Ge and As compounds have been explained in terms of some key physical parameters.This work was supported by the Scientific and Technical Research Council of Turkey (TUB¨ ˙ITAK) (Project No. MFAG- 114F192). Some of the calculations for this project were carried out using the computing facilities on the Intel Nehalem (i7) cluster (ceres) in the School of Physics, University of Exeter, United Kingdo

Ab initio investigation of electron-phonon interaction in LaSn3 and CaSn3

This is the author accepted manuscript. The final version is available from Taylor & Francis via the DOI in this recordWe present results for the structural, electronic, vibrational, and electron-phonon coupling properties of LaSn and CaSn adopting the simple cubic AuCu-type structure obtained using the the generalised gradient approximation of the density functional theory and plane wave ab initio pseudopotential method. Our electronic results show that both materials display metallic character with several bands, which have mainly Sn 5p character, crossing the Fermi level. The calculated phonon spectrum of LaSn accords very well with reported experimental measurements. The weights of the peaks in the Eliashberg spectral function of both compounds are enhanced with the use of experimental lattice constant in our electron-phonon calculation, increasing the value of average electron phonon coupling parameter from 0.876 to 0.937 for LaSn (by 7) and from 0.642 to 0.725 for CaSn (by 13). The use of experimental lattice constant also improves the agreement between theoretical and experimental values of the superconducting temperature for both compounds

The effect of spin orbit interaction for superconductivity in the noncentrosymmetric superconductor CaIrSi3

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.We have carried out an ab initio study of the electronic, vibrational and electron-phonon interaction properties of the body-centred tetragonal CaIrSi3 by employing the density functional theory, a linear-response formalism, and the plane-wave pseudopotential method. The electronic structure and phonon dispersion relations of this material have been analyzed with and without the inclusion of spin-orbit interaction (SOI). Our electron-phonon interaction results reveal that Si-related phonon modes are more involved in the process of scattering of electrons than the remaining phonon modes due to considerable existence of the Si 3p states near the Fermi level. By integrating the Eliashberg spectral function, the average electron-phonon coupling parameter is found to be 0.58 which compares very well with its experimental value of 0.56. Using the calculated value of λ, the superconducting critical temperature (Tc) for CaIrSi3 is found to be 3.20 K which is in good accordance with its experimental value of 3.55 K. Furthermore, we have shown that the effect of SOI on the values of λ and Tc is very small.This work was supported by the Scientific and Technical Research Council of Turkey (TÜBİTAK) (Project Number MFAG-115F135)

The effect of spin orbit interaction on the physical properties of LaTSi3 (T = Ir, Pd, and Rh): First-principles calculations

This is the final version of the article. Available from AIP Publishing via the DOI in this record.We have presented the structural, elastic, electronic, phononic, and electron-phonon interaction properties of the La-based noncentrosymmetric superconductors, such as LaIrSi3, LaRhSi3, and LaPdSi3, by using the generalized gradient approximation of the density functional theory. The calculated elastic constants reveal the mechanical stability of all the studied compounds in their noncentrosymmetric structure, while the lack of inversion symmetry gives rise to lift the degeneracy of their electronic bands, except in the Γ-Z and X-P directions. The calculated Eliashberg spectral function shows that all phonon branches of these materials couple considerably with electrons, and thus, all of them make contribution to the average electron-phonon coupling parameter λ. Using the calculated values of λ and the logarithmically averaged phonon frequency ωln, the superconducting critical temperature Tc values for LaIrSi3, LaRhSi3, and LaPdSi3 are estimated to be 0.89, 2.56, and 2.40 K, respectively, which accord very well with their corresponding experimental values of 0.77, 2.16, and 2.60 K.This work was supported by the Scientific and Technical Research Council of Turkey (TÜBİTAK) (Project No. MFAG-115F135)

Theoretical investigation of electron-phonon interaction in the orthorhombic phase of Mo2C

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record We have studied the structural, electronic, elastic, mechanical, vibrational and electron-phonon interaction properties of Mo 2 C crystallizing in the simple orthorhombic ζ-Fe 2 N-type crystal structure by using the generalized gradient approximation of the density functional theory and the plane wave ab initio pseudopotential method. A critical assessment of the calculated electronic structure and density of states reveals that the bonding in this material is a combination of covalent, ionic and metallic in nature. The calculated values of the second order elastic constants signal its mechanical stability. An examination of the calculated Eliashberg spectral function reveals that Mo-related phonon modes couple strongly to electrons due to the significant presence of Mo d electrons at the Fermi energy. From the integration of this spectral function, the value of average electron-phonon coupling parameter is determined to be of the intermediate strength 0.709. Finally, the value of the superconducting critical temperature is calculated to be 7.37 K, in excellent accordance with its measured value of 7.30 K

Ab initio investigation of spin orbit coupling effect on the physical properties of IrGe superconductor

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record We have aimed to explore the influence of spin orbit coupling (SOC) on the electronic, elastic, mechanical, lattice dynamical and electron-phonon interaction properties of the simple orthorhombic IrGe using first principles density functional calculations within the generalized gradient approximation. The effect of SOC on the above properties of IrGe is mainly associated with Ir atom which possesses a 5d orbital and much heavier mass than that of Ge atom. The calculated values of nine independent elastic constants satisfy all the stability criteria, indicating that IrGe is mechanically stable in its MnP-type crystal structure. Also, no imaginary phonon frequencies are found in the phonon dispersion curves, indicating the dynamical stability of IrGe in its orthorhombic structure. Inclusion of SOC leads to the hardening of some low-frequency phonon modes which influences the electron-phonon interaction. Furthermore, inclusion of SOC leads to a decrease in dominant peaks of the Eliashberg function, and thus decrease in the values of the electron-phonon scattering parameter λ as well as the superconducting transition temperature T c . Using the calculated value of λ with SOC, the value of T c is obtained to be 5.09 K which compares very well with the recent measured value of 5.17 K