Self-Doping Induced Orbital-Selective Mott Transition in Hg2Ru2O7

Pyrochlore oxides are fascinating systems where strong, multi-orbital correlations in concert with geometrical frustration give rise to unanticipated physical properties. The detailed mechanism of the insulator-metal transitions (IMT) underpinning these phenomena is, however, ill-understood in general. Motivated thereby, we study the IMT in the pyrochlore ${\rm Hg_{2}Ru_{2}O_{7}}$ using LDA+DMFT. In contrast to the well-known examples of Mott transitions in TMO, we show that, in the negative charge-transfer situation characteristic of \hg, self-doping plays a crucial role in the emergence of an orbital-selective IMT. We argue that this mechanism has broader relevance to other correlated pyrochlore oxides.Comment: 5 pages, 3 figure

Coulomb repulsion and correlation strength in LaFeAsO from Density Functional and Dynamical Mean-Field Theories

LDA+DMFT (Local Density Approximation combined with Dynamical Mean-Field Theory) computation scheme has been used to calculate spectral properties of LaFeAsO -- the parent compound for new high-T$_c$ iron oxypnictides. Coulomb repulsion $U$ and Hund's exchange $J$ parameters for iron 3d electrons were calculated using \textit {first principles} constrained density functional theory scheme in Wannier functions formalism. Resulting values strongly depend on the number of states taken into account in calculations: when full set of O-$2p$, As-$4p$, and Fe-3d orbitals with corresponding bands are included, computation results in $U=3\div$4 eV and J=0.8 eV. In contrast to that when the basis set is restricted to Fe-3d orbitals and bands only, computation gives much smaller parameter values $F^0$=0.8 eV, $J$=0.5 eV. However, DMFT calculations with both parameter sets and corresponding to them choice of basis functions result in weakly correlated electronic structure that is in agreement with experimental X-ray and photoemission spectra.Comment: 13 pages, 9 figure

Nuclear magnetic relaxation and superfluid density in Fe-pnictide superconductors: An anisotropic \pm s-wave scenario

We discuss the nuclear magnetic relaxation rate and the superfluid density with the use of the effective five-band model by Kuroki et al. [Phys. Rev. Lett. 101, 087004 (2008)] in Fe-based superconductors. We show that a fully-gapped anisotropic \pm s-wave superconductivity consistently explains experimental observations. In our phenomenological model, the gaps are assumed to be anisotropic on the electron-like \beta Fermi surfaces around the M point, where the maximum of the anisotropic gap is about four times larger than the minimum.Comment: 10 pages, 8 figures; Submitted versio

Normal-state correlated electronic structure of iron pnictides from first principles

We describe the correlated electronic structure of a prototype Fe-pnictide superconductor, $SmO_{1-x}F_{x}FeAs$, using LDA+DMFT. Strong, multi-orbital electronic correlations generate a low-energy pseudogap in the undistorted phase, giving a bad, incoherent metal in qualitative agreement with observations. Very good semi-quantitative agreement with the experimental spectral functions is seen, and interpreted, within a correlated, multi-orbital picture. Our results show that Fe-pnictides should be understood as low-carrier density, incoherent metals, in resemblance to the underdoped cuprate superconductors.Comment: 4 pages, 3 figure