Theoretical examination of superconductivity in the cubic antiperovskite Cr3GaN under pressure

This is the final version of the article. Available from AIP via the DOI in this record.We present results of a first-principles investigation of the lattice dynamics and electron-phonon coupling of Cr3GaN under pressure within a linear response approach based on density functional perturbation theory. It is found that stable phonon modes are maintained throughout the Brillouin zone in the pressure range 0-100 GPa. Our results at zero pressure indicate that the material is a conventional electron-phonon superconductor with intermediate level of coupling strength. It is further found that the decrease in the density of states at the Fermi level and the increase of phonon frequencies under pressure are the main causes for a monotonic decrease of the electron-phonon coupling parameter and the superconductor transition temperature. © 2013 AIP Publishing LLC

Ab initio calculations of surface phonons of the hydrogen-terminated Si(110)-(1 × 1) surface

A first-principles study, using a linear-response approach based on the pseudopotential method and the generalised gradient approximation, has been made to examine the phonon spectrum of the hydrogen-terminated Si(110)-(1 × 1) surface. The calculated results compare very well with the results determined from a recent high-resolution electron-energy-loss spectroscopy measurement. In particular, the energy locations and polarization characteristics of the H-Si bond bending and H-Si stretching surface phonon modes have been determined and discussed in detail. The zone-centre splitting of the two H-Si stretching surface phonon modes is found to be 2.4 meV, which compares very well with the experimental value of 1.9 meV

Theoretical investigation of superconductivity in ternary silicide NaAlSi with layered diamond-like structure

© 2016 Informa UK Limited, trading as Taylor & Francis Group.We have investigated the electronic structure, phonon modes and electron-phonon coupling to understand superconductivity in the ternary silicide NaAlSi with a layered diamond-like structure. Our electronic results, using the density functional theory within a generalized gradient approximation, indicate that the density of states at the Fermi level is mainly governed by Si p states. The largest contributions to the electron-phonon coupling parameter involve Si-related vibrations both in the x-y plane as well as along the z-axis in the x-z plane. Our results indicate that this material is an s-p electron superconductor with a medium level electron-phonon coupling parameter of 0.68. Using the Allen-Dynes modification of the McMillan formula we obtain the superconducting critical temperature of 6.98 K, in excellent agreement with experimentally determined value of 7 K

Electron–phonon interaction and superconductivity in the borocarbide superconductor

This is the author accepted manuscript. The final version is available from Taylor & Francis via the DOI in this record.We have made an ab initio investigation of electron–phonon interaction and superconductivity in the borocarbide super-conductor ScNi 2 B 2 C adopting the body-centred tetragonal LuNi 2 B 2 C-type of layered crystal structure. The calculated electronic structure and density of states suggest that the bonding is a combination of covalent, ionic and metallic in nature and that the Fermi level falls in one of the peaks in the electronic density of states. Our electron–phonon interaction calculations suggest that the mechanism for superconductivity is heavily governed by interactions of electrons with acoustic phonon modes and low-frequency optical phonon modes, which strongly modulate NiB 4 tetrahedral bond angles. By integrating the Eliashberg spectral function, the value of average electron–phonon coupling parameter is found to be 0.93 and the superconducting critical temperature is calculated to be 16.28 K, in excellent agreement with the experimentally reported value of 16.0 K

Ab initio investigation of superconductivity in orthorhombic MgPtSi

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Available online 3 March 2016We have performed an ab initio study of electronic, vibrational and superconducting properties of the orthorhombic MgPtSi by employing the density functional theory, a linear-response formalism, and the plane-wave pseudopotential method. Our electronic results suggest that the density of states at the Fermi level is primarily contributed by Pt 5d and Si 3p states with much smaller contribution from Mg electronic states. Phonon anomalies have been found for all three acoustic branches. Due to these phonon anomalies, the acoustic branches make large contributions to the average electron-phonon coupling parameter. From the Eliashberg spectral function, the value of average electron-phonon coupling parameter is found to 0.707. Using this value, the superconducting critical temperature is obtained to be 2.4 K, in excellent accordance with its experimental value of 2.5 K

Electron-phonon superconductivity in the filled skutterudites LaRu4P12, LaRu4As12, and LaPt4Ge12

This is the final version of the article. Available from American Physical Society via the DOI in this record.We have reported on the structural, elastic, electronic, lattice dynamical and electron-phonon interaction properties of LaT4X12 (T=Ru, Pt and X=P, As, Ge) by using the generalized gradient approximation of the density functional theory and the plane-wave pseudopotential method. These lanthanum-filled skutterudites are found to be characterized with a flat band, resulting in a sharp peak in the electronic density of states, near the Fermi level. The lattice dynamical properties of these materials change considerably when the P atom is replaced by larger As or Ge atoms. The Migdal-Eliashberg approach is used to determine the Eliashberg spectral function for all the considered compounds. Using the calculated Eliashberg spectral function, the value of average electron-phonon coupling parameter is found to be 0.74 for LaRu4P12, 1.03 for LaRu4As12, and 1.08 for LaPt4Ge12. The superconducting critical temperature (Tc) values for LaRu4P12, LaRu4As12, and LaPt4Ge12 are estimated to be 6.95, 11.56, and 8.32 K, respectively, which compare well enough with their experimentally measured values of 7.2, 10.45, and 8.23 K.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

Electron-phonon superconductivity in the ternary phosphides BaM2 P2 (M=Ni,Rh,and Ir)

This is the final version of the article. Available from American Physical Society via the DOI in this record.Ab initio plane-wave pseudopotential calculations of electronic and vibrational properties have been carried out for the ternary phosphides BaM2P2 (M=Ni,Rha and Ir) with a ThCr2Si2-type structure. The calculated electronic results show the metallic character of BaM2P2, and the plots of total and partial density of states of BaM2P2 exhibit strong hybridization between the d states of the M atom and the p states of the P atom below the Fermi energy. Differences in the phonon spectrum and density of states both in the acoustical and optical ranges for these compounds are presented and discussed. The Eliashberg spectral function for these compounds has been calculated by using a linear response approach based on the density functional theory. By integrating the Eliashberg spectral function, the average electron-phonon coupling parameter (λ) is determined to be 0.61 for BaNi2P2, 0.55 for BaIr2P2, and 0.43 for BaRh2P2. Using the calculated values of λ and the logarithmically averaged phonon frequency ωln the superconducting critical temperature (Tc) values for BaNi2P2,BaIr2P2, and BaRh2P2 are obtained to be 2.80, 1.97, and 0.70 K, respectively, which compare very well with their experimental values of 3.0, 2.1, and 1.0 K.This work was supported by the Scientific and Technical Research Council of Turkey (TÜBİTAK) (Project Number 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 Kingdom

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