We here present how a self-consistent solution of the dynamical mean-field theory equations can be obtained using exact diagonalization of an Anderson impurity model with accuracies comparable to those found using renormalization group or quantum Monte Carlo methods. We show how one can solve a correlated quantum impurity coupled to several hundred uncorrelated bath sites, using a restricted active basis set. The number of bath sites determines the resolution of the obtained spectral function, which consists of peaks with an approximate spacing proportional to the bandwidth divided by the number of bath sites. The self-consistency cycle is performed on the real-frequency axis and expressed as numerical stable matrix operations. The same impurity solver has been used on ligand field and finite size cluster calculations and is capable of treating involved Hamiltonians including the full rotational invariant Coulomb interaction, spin-orbit coupling, and low-symmetry crystal fields. The proposed method allows for the calculation of a variety of correlation functions at little extra cost

Ultrafast spectroscopy reveals coherent oscillations of a phonon-coupled BEC of excitons in an excitonic insulator.

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We have used Raman scattering to investigate the magnetic excitations and lattice dynamics in the prototypical spin-orbit Mott insulators Sr2IrO4 and Sr3Ir2O7. Both compounds exhibit pronounced two-magnon Raman scattering features with different energies, lineshapes, and temperature dependencies, which in part reflect the different influence of long-range frustrating exchange interactions. Additionally, we find strong Fano asymmetries in the lineshapes of low-energy phonon modes in both compounds, which disappear upon cooling below the antiferromagnetic ordering temperatures. These unusual phonon anomalies indicate that the spin-orbit coupling in Mott-insulating iridates is not sufficiently strong to quench the orbital dynamics in the paramagnetic state.PACS numbers: 71.70. Ej, 75.25.Dk, 75.47.Lx, The recent discovery of Mott-insulating states driven by the confluence of intra-atomic spin-orbit coupling and electronic correlations ("spin-orbit Mott insulators") has triggered a wave of research on novel magnetic ground states and excitations. The most widely studied spinorbit Mott insulators are iridium oxides based on Ir 4+ions with electron configuration 5d 5 and total angular momentum j eff = 1 2 . Mott-insulating iridates with j effpseudospins arranged on geometrically frustrated lattices are promising candidates for spin-liquid states with unusual transport properties and fractionalized excitations. [1][2][3][4][5] Iridates with square-lattice geometries, on the other hand, have been extensively investigated as possible analogues of the cuprate high-temperature superconductors whose low-energy excitations are characterized by the pure spin quantum number S = 1 2 . Indeed, resonant inelastic x-ray scattering (RIXS) experiments [6] have shown that the magnon excitations of the prototypical square-lattice antiferromagnet Sr 2 IrO 4 are well described by the Heisenberg model, in close analogy to those of the isostructural Mott-insulator La 2 CuO 4 . Very recently, experiments on doped Sr 2 IrO 4 have uncovered tantalizing evidence of a Fermi surface split up into disjointed segments ("Fermi arcs") [7] and a lowtemperature gap with d-wave symmetry [8,9], which are hallmarks of the doped cuprates. [10] This rapidly advancing research frontier has raised fundamental questions about the microscopic electronic structure of spin-orbit Mott insulators. A particularly important question concerns the orbital degeneracy, which plays a central role in the phase behavior of 3d-electron materials, where the spin-orbit coupling is negligible. In the widely studied manganates, for instance, the orbital degeneracy of the manganese ions is only partially lifted by crystalline electric fields, and coupling of low-lying orbital excitations to lattice distortions leads to the formation of polarons which dominate the physical properties of the doped manganates. In Mottinsulating cuprates, on the other hand, the S = 1 2 moments of the orbitally non-degenerate Cu 2+ ions do not couple significantly to the crystal lattice, so that spin...