Ertuǧrul Karaca

First-principles investigation of superconductivity in the body-centred tetragonal

We have investigated the ground state and electronic properties of in the structure using a generalised gradient approximation of the density functional theory and the ab initio pseudopotential method. We find that the calculated electronic properties of exhibit three-dimensional rather than two-dimensional characteristics in spite of the apparent two dimensionality in its atomic structure. An interesting feature of the phonon dispersion curves is the phonon anomaly in the lowest transverse acoustic branch as well as the longitudinal acoustic branch. We have shown that these phonon anomalies give rise to large electron-phonon interaction, as is evident from the calculated Eliashberg spectral function F(). By integrating this spectral function, the value of average electron-phonon coupling parameter is calculated to be 0.85, from which the superconducting critical temperature is estimated to be 3.74 K, in gratifying accord with its experimental value of 4.0 K.

Electron–phonon interaction and superconductivity in the

Abstract Based on first-principles pseudopotential plane-wave method within the generalised gradient approximation, we have studied the structural, electronic, vibrational and BCS superconducting properties of . The calculated electronic properties for depict three-dimensional rather than two-dimensional characteristics in spite of the apparent two-dimensionality in its atomic structure. At the zone centre only three (La–La optical) and the single (Ni–Ni optical) phonon modes couple strongly with electrons. However, a critical assessment of the Eliashberg spectral function throughout the Brillouin zone reveals that all phonon modes except the two highest frequency phonon modes couple considerably with the electrons at the Fermi energy. By integrating the Eliashberg spectral function, the values of the average electron–phonon coupling constant and the logarithmic average frequency are found to be 0.73 and 301.23 K, respectively. Inserting these values into the Allen–Dynes formula with using a reasonable value of = 0.10 for the effective Coulomb repulsion parameter, the value of superconducting transition temperature is found to be 11.61 K which compares well with its experimental values of 12–13 K and 11.7 K.

Electron–phonon interaction and superconductivity in the borocarbide superconductor

Abstract We have made an ab initio investigation of electron–phonon interaction and superconductivity in the borocarbide super-conductor adopting the body-centred tetragonal -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 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.

Physical properties of the body-centred tetragonal

Abstract We have investigated the structural, elastic, electronic, and lattice dynamical properties of in the body-centred tetragonal structure using a generalised gradient approximation of the density functional theory and the ab initio pseudopotential method. The calculated second-order elastic constants indicate that is mechanically stable and behaves in a ductile manner. Our electronic results show that the states close to the Fermi level are primarily contributed by Pd d and Ge p orbitals. A detailed analysis of electron–phonon interaction calculations reveals that the mechanism for superconductivity in is mainly governed by interactions of Pd d and Ge p electrons around the Fermi level with acoustic phonon modes and low-frequency optical phonon modes, which strongly change PdGe tetrahedral bond angles. The values of the average electron–phonon coupling constant and the logarithmic average frequency are calculated to be 0.66 and 77.3 K, respectively. Inserting these values into the Allen–Dynes formula with using an acceptable value of for the effective Coulomb repulsion parameter, the value of superconducting transition temperature is obtained to be 1.69 K, which is in excellent agreement with its experimental value.

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

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.