The spectra of Pu chalcogenides and pnictides are computed with LDA+DMFT and interpreted with the aid of valence histograms and slave-boson calculations. We find the chalcogenides are mixed-valent (n f = 5.2) materials with a strongly T -dependent low-energy density of states and a triplet of quasiparticle peaks below the Fermi level. Furthermore, we predict a doublet of reflected peaks above the Fermi level. In the pnictides, the raising of f 6 states relative to f 5 suppresses valence fluctuations, resulting in integral-valent (n f = 5.0) local moment metals.

A family of topological semimetallic phases where two-fold degenerate gapless points form linked rings is introduced. We refer to this phase as Weyl-link semimetals. A concrete two-band model with two linked nodal lines is constructed. We demonstrate that the Chern-Simons 3-form depends on the linking number of rings in a generic two-band model. In addition, we show the emergence of zero-energy modes in the Landau level spectrum can reveal the location of nodal lines, providing a method of probing their linking number. INTRODUCTIONThe application of topology to condensed matter physics has produced rich insights into the behavior of an entire class of materials. The integer quantum Hall state, as well as topological insulators and superconductors [1][2][3][4][5][6], are characterized by the topology of their ground state wave function. These topological structures give rise to protected gapless boundary modes and quantized electromagnetic and gravitomagnetoelectric responses [7,8]. In addition to fully gapped topological phases, semimetals and nodal superconductors can also exhibit interesting topological properties. Of particular interest are Weyl semimetals [9][10][11], where the band touching points in the bulk behave as monopoles in momentum space. These monopoles are sources and drains of Berry flux, which leads to anomalous electromagnetic transport and the emergence of surface Fermi arcs. In addition to Weyl semimetals, the set of gapless points in the bandstructure can also form one-dimensional nodal lines and rings [12][13][14][15]. These nodal-ring semimetals and superconductors also exhibit robust drumhead surface states [13,16]. Many material candidates have been proposed and some have been experimentally confirmed [17][18][19][20][21][22][23][24][25][26][27].In general, the complexity of gapless phases is richer than gapped phases in the following sense: gapped phases are like a featureless vacuum while the point and line nodes in gapless phases behave as defects in momentum space carrying topological charge. As mentioned above, point nodes behave like monopoles of Berry flux, while line nodes are akin to flux tubes (or solenoids). The interplay between these momentum defects often leads to observable effects. For example, nodal points and lines can coexist in the momentum space [28]. Nodal lines can intersect to form states termed nodal-chains [29,30]. Finally, the line defects can share termination points which can be seen as the momentum space equivalent of the real space nexus previously discussed in helium-3 [31][32][33].We extend the family of gapless phases by constructing a minimal two-band model containing two linked nodal rings, with the linking number controlled by an integer n. We refer to this phase as a Weyl-link semimetal (WLSM). Similar to a nodal-ring semimetal, the non-vanishing Berry phase around the nodal rings in a WLSM leads to drumhead surface states. We show the Chern-Simons 3-form can serve as a topological invariant of the linking number of nodal rings in the two-band model...

An optical study of fully strained ultrathin LaNiO3 films is presented and compared with LDA+DMFT calculations. LaNiO3 films were grown by pulsed laser deposition on LaAlO3 and SrTiO3 substrates which provide compressive and tensile strain, respectively. Optical conductivity data show a Drude peak with a spectral weight that is significantly reduced compared to that obtained from LDA calculations. The extended Drude analysis reveals the presence of a pseudogap around 80 meV for the film on SrTiO3 and near 40 meV, at low temperature only, for the film on LAO. An unusual temperature dependence of the optical conductivity is observed, with the Drude plasma frequency increasing by up to 20% at low temperature due to spectral weight transfer from bands lying 2-4 eV below the Fermi energy. Such a strong temperature dependence of the Drude spectral weight has previously been reported for correlated electron systems in which a phase transition is present. In LNO however, no phase transition is observed.

Motivated by the commonplace observation of Mott insulators away from integer filling, we construct a simple thermodynamic argument for phase separation in first-order doping-driven Mott transitions. We show how to compute the critical dopings required to drive the Mott transition using electronic structure calculations for the titanate family of perovskites, finding good agreement with experiment. The theory predicts that the transition is percolative and should exhibit Coulomb frustration.