Theoretical Study of Coulomb Correlations and Spin-Orbit Coupling in SrIrO3

Given that energy scales associated with crystal field splitting, spin orbit coupling and coulomb correlations in iridates are comparable, hence leading to exotic properties, we investigate the physical properties of orthorhombic SrIrO3 using density functional theory. Our calculations, however, show that SrIrO 3 is a bad metal with no long range magnetic ordering, unlike its sister compounds Sr2IrO4 and Sr3Ir2O7. Moreover, despite having large band width, it appears conclusive that the larger resistivity in SrIrO 3 is due to spin orbit interactions. Besides, the effects of electron-electron correlations on its electronic structure and magnetic properties are also discussed

Cooperative effects of lattice and spin-orbit coupling on the electronic structure of orthorhombic SrIrO3

Orthorhombic SrIrO3 subjected to strain show tunable transport properties. With underlying symmetry remaining invariant, these properties are associated with IrO6 octahedral tilting. Adopting to first-principles methods, the effects of crystal field, spin-orbit coupling, and Coulomb correlations, on comparable interaction length scales, are discussed. While tilting induces a t2g-eg crystal-field splitting and band narrowing, spin-orbit coupling induces a partial splitting of the Jeff bands rendering SrIrO3 a semi-metallic ground state. The SOC enhanced hybridization of Ir-O orbitals, serve as a explanation to why the critical Hubbard correlation strength increases with increasing SOC strength in SrIrO3 to induce an insulating phase

Structure of Sn_1-xGe_x random alloys as obtained from the coherent potential approximation

The structure of the Sn1-xGex random alloys is studied using density functional theory and the coherent potential approximation. We report on the deviation of the Sn1-xGex alloys from Vegard's law, addressing their full compositional range. The findings are compared to the related Si1-xGex alloys and to experimental results. Interestingly, the deviation from Vegard's law is quantitatively and qualitatively different between the Sn1-xGex and Si1-xGex alloys. An almost linear dependence of the bulk modulus as a function of composition is found for Si1-xGex, whereas for Sn1-xGex the dependence is strongly nonlinear

Electronic structure of Zr-Ni-Sn systems: role of clustering and nanostructures in Half-Heusler and Heusler limits

Half-Heusler and Heusler compounds have been of great interest for several decades for thermoelectric, magnetic, half-metallic and many other interesting properties. Among these systems, Zr-Ni-Sn compounds are interesting thermoelectrics which can go from semiconducting half-Heusler (HH) limit, ZrNiSn, to metallic Heusler (FH) limit, ZrNi$_2$Sn. Recently Makogo et al. [J. Am. Chem. Soc. 133, 18843 (2011)] found that dramatic improvement in the thermoelectric power factor of HH can be achieved by putting excess Ni into the system. This was attributed to an energy filtering mechanism due to the formation of FH nanostructures in the HH matrix. Using density functional theory we have investigated clustering and nanostructure formation in HH$_{1-x}$FH$_x$ systems near the HH and FH ends and found that excess Ni atoms in HH tend to stay close to each other and form nanoclusters of FH. On the other hand, there is competing interaction between Ni-vacancies in FH which prevent them from forming HH nano clusters. Effects of nano inclusions on the electronic structure at both HH and FH ends will be discussed.Comment: Published in J. Phys.: Condens. Matte

Magnetic phase diagram of Fe1.1Te1-xSex: A comparative study with the stoichiometric superconducting FeTe1-xSex system

We report a comparative study of the series Fe1.1Te1-xSex and the stoichiometric FeTe1-xSex to bring out the difference in their magnetic, superconducting and electronic properties. The Fe1.1Te1-xSex series is found to be magnetic and its microscopic properties are elucidated through Moessbauer spectroscopy. The magnetic phase diagram of Fe1.1Te1-xSex is traced out and it shows the emergence of spin-glass state when the antiferromagnetic state is destabilized by the Se substitution. The isomer shift and quadrupolar splitting obtained from the Moessbauer spectroscopy clearly brings out the electronic differences in these two series.Comment: 6 pages, 9 figure

\delta-doped LaAlO3-SrTiO3 interface: Electrical transport and characterization of the interface potential

Here we investigate LaAlO_3-SrTiO_3 heterostructure with\delta-doping of the interface by LaMnO_3 at less than one monolayer. This doping strongly inhibits the formation of mobile electron layer at the interface. This results in giant increase of the resistance and the thermopower of the heterostructure. Several aspects of this phenomena are investigated. A model to calculate the carrier concentration is presented and effect of doping and detailed temperature dependence is analyzed in terms of model parameters and the weak-scattering theory. The large enhancement of thermopower is attributed to the increased spin and orbital entropy originating from the LaMnO_3 mono-layer

LaScO3/SrTiO3: A conducting polar heterointerface of two 3d band insulating perovskites

This work reports a quasi-two-dimensional electron gas (q-2DEG) system at the interface of two wideband-gap insulators, (TiO2-terminated) SrTiO3 and LaScO3, with a minimum thickness of 4-unit cell (uc). The highly crystalline and abrupt heterointerface is confirmed with high-resolution electron microscopy. The mixed Ti4+ and Ti3+ valence states (for 4 uc of LaScO3) obtained from the x-ray photoelectron spectroscopy study suggest an intrinsic electronic reconstruction at the interface, leading to a metallic nature. This origin is well supported by density functional theory calculations that reveal an emergence of 3.3 states/eV/spin at the Fermi level for 4 uc in accordance with the polar catastrophe model. The study offers one more perovskite heterostructure, like LaAlO3/SrTiO3, for unraveling the q-2DEG phenomena toward a clear mechanism and futuristic applications