arXiv subjects

M. J. Winiarski

Publications and source records attributed to M. J. Winiarski.

26 records · Page 2Linked to original sources

arXiv2014

Electronic structure of non-centrosymmetric superconductors Re24(Nb;Ti)5 by ab initio calculations

Electronic structures of superconducting Re24Nb5 and Re24Ti5 have been calculated employing the full-potential local-orbital method within the density functional theory. The investigations were focused on the influence of the antisymmetric spin-orbit coupling on band structures and Fermi surfaces of these non-centrosymmetric systems. The predicted here density of states at the Fermi level for Re24Ti5 is abnormally low with respect to that deduced from previous heat capacity measurements. This discrepancy suggests an intermediate coupled superconducting state in Re24Ti5. The differences between electronic properties of both compounds could explain more robust superconductivity in the Nb-based material.

cond-mat.supr-con↗

arXiv2014

The electronic structure of CeNiGe3 and YNiGe3 superconductors by ab initio calculations

Band structures of pressure-induced CeNiGe3 and exotic BCS-like YNiGe3 superconductors have been calculated employing the full-potential local-orbital code. Both the local density approximation (LDA) and LDA+U treatment of the exchange-correlation energy were used. The investigations were focused on differences between electronic properties of both compounds. Our results indicate that the Ce-based system exhibits higher density of states at the Fermi level, dominated by the Ce 4f states, in contrast to its non f-electron counterpart. The Fermi surface (FS) of each compound originates from three bands and consists of both holelike and electronlike sheets. The specific FS nesting properties of only CeNiGe3 enable an occurrence of spin fluctuations of a helicoidal antiferromagnetic character that may lead to unconventional pairing mechanism in this superconductor. In turn, the topology of the FS in YNiGe3 reveals a possibility of multi-band superconductivity, which can explain the observed anomalous jump at Tc in its specific heat.

cond-mat.supr-con↗

arXiv2014

Strain effects on electronic structure and superconductivity in the iron telluride

The influence of tensile strain in the ab-plane on crystal and electronic structure of FeTe has been studied ab initio. In superconducting FeSe the Fermi surface nesting with a vector q~(0.5,0.5)(2π/a) is believed to be crucial for rising superconductivity mediated by spin-fluctuations. The results presented here indicate that tensile-strained FeTe also exhibits such conditions. Furthermore, the Fermi surface changes, related to the increase of the lattice parameter a of this telluride, are opposite to analogous effects reported for FeSe. Since a recently reported transition from the double-stripe to the single-stripe magnetic order in FeTe under tensile strain in the ab-plane is associated with an occurence of superconductivity in corresponding thin films, these findings allow for drawing a consistent picture of superconductivity in FeSe(1-x)Te(x) systems, in general.

cond-mat.supr-con↗

arXiv2013

Magnetic phase transitions and superconductivity in strained FeTe

The influence of hydrostatic pressure and ab-plane strain on the magnetic structure of FeTe is investigated from first principles. The results of calculations reveal a phase transition from antiferromagnetic double-stripe ordering at ambient pressure to ferromagnetic ordering at 2 GPa, or under compressive strain reducing the lattice parameter a by about 3%. In turn, a tensile strain of less than 2% induces the phase transition to antiferromagnetic single-stripe ordering. It corresponds to the superconducting FeTe thin films, thereby confirming that the superconducting state is positively linked to single-stripe antiferromagnetic fluctuations. Both types of transition indicate that the position of Te atoms in the crystal is crucial for the magnetic and superconducting properties of iron chalcogenides.

cond-mat.supr-con↗

arXiv2013

Strain effects on the electronic structure of the FeSe0.5Te0.5 superconductor

The electronic structure of the strained FeSe0.5Te0.5 superconductor has been investigated from first principles. Our calculation results indicate that the influence of hydrostatic, biaxial or uniaxial compressive stress on the density of states at the Fermi level is insignificant. The overall shape of the Fermi-surface (FS) nesting function for FeSe0.5Te0.5 at ambient pressure resembles that of its parent compound, FeSe, but under the ab-plane compressive strain. In these two systems, changes of their FSs under various stress conditions are qualitatively almost the same. However, in FeSe0.5Te0.5 the intensity of the perfect Q=(0.5,0.5)*(2π/a) nesting vector is more diminished. These findings are in good agreement with former experimental data and support the idea of spin-fluctuation mediated superconductivity in iron chalcogenides.

cond-mat.supr-con↗

arXiv2013

Strain effects on electronic structure of the iron selenide superconductor

The influence of various strains on crystal and electronic structures of superconducting FeSe has been studied ab initio. We consider changes in the Fermi surface nesting with a vector Q=(0.5,0.5)*(2π/a) as crucial for rising superconductivity (SC) mediated by spin-fluctuations (SF). Our results indicate that the c-axis strained FeSe exhibits the most imperfect nesting, which enhances SF and, hence, also SC. In turn, the ab-plane compressive strain slightly weakens this} nesting while the tensile strain destroys it completely. These findings are consistent with reported earlier experimental dependencies of superconducting transition temperatures on strain in FeSe thin films.

cond-mat.supr-con↗

arXiv2013

The substitution effects on electronic structure of iron selenide superconductors

The influence of a partial substitution with S, Te, Co, Ni and Cu atoms on the electronic structure of the FeSe superconductor has been investigated within the density functional theory. The results of the supercell calculations reveal distinct changes of electronic structures of the substituted FeSe systems, which can be responsible for their superconducting properties. The replacement of Se atoms by Te or S ones yields imperfect nesting between the holelike and electronlike Fermi surface (FS) sheets, which enhances magnetic fluctuations responsible for superconducting pairing, thus leading to higher values of the superconducting critical temperatures. Meanwhile, the substitutions with transition-metal atoms for iron sites make more substantial changes of the FSs topology, since the holelike cylinders shrink at the cost of an enlargement of the electronlike ones. Thus, the superconducting pairing, driven by the nesting between these sheets, weakens and superconductivity disappears for a small percentage of dopants. The results support the idea of spin-fluctuation mediated superconductivity in iron chalcogenides.

cond-mat.supr-con↗

arXiv2012

The Pressure Effects on Electronic Structure of Iron Chalcogenide Superconductors FeSe$_{1-x}$Te$_x$

We study the electronic structure of iron-based superconductors FeSe$_{1-x}$Te$_x$ within the density functional theory. We pay particular attention to the pressure effects on the Fermi surface (FS) topology, which seem to be correlated with a critical superconducting temperature TC of iron chalcogenides and pnictides. A reduction of the FS nesting between hole and electron cylinders with increasing pressure is observed, which can lead to higher values of TC . The tellurium substitution into selenium sites yields FS changes similar to the pressure effect.

cond-mat.supr-con↗