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We investigate the metal-to-insulator phase transition driven by the density-density electronic interaction in the quarter-filled model on a cubic lattice with two orbitals split by a crystal field. We show that a systematic consideration of the non-local collective electronic fluctuations strongly affects the picture of the phase transition provided by the dynamical mean field theory. Our calculations reveal the appearance of metallic and Mott insulating states characterised by the same density but different values of the chemical potential, which is missing in the local approximation to electronic correlations. We find that the region of concomitant metastability of these two solutions is remarkably broad in terms of the interaction strength. It starts at a critical value of the interaction slightly larger than the bandwidth and extends to more than twice the bandwidth, where the two solutions merge into a Mott insulating phase. Our results illustrate that non-local correlations can have crucial consequences on the electronic properties in the strongly correlated regime of the simplest multi-orbital systems.

We compute scattering rates for electrons in the two-dimensional Hubbard model for a one-orbital metal and a two-orbital band insulator by means of the Boltzmann scattering equation (BSE) and dynamical mean-field theory (DMFT). As an intermediate method between both, we also consider the BSE without momentum conservation. In the weak interaction regime and for the band insulator, the last two agree to very good accuracy. The BSE with momentum conservation, on the other hand, shows slightly larger scattering rates, and a momentum differentiation of these on the Fermi surface. For the Mott insulator at strong interaction, the DMFT electron scattering rates are much larger and defy a BSE description. Noteworthy, the scattering rates for the band insulator are exceedingly small because -- in contrast to the Mott insulator -- there is virtually no impact ionization., Comment: 15 pages, 12 figures

We present a dynamical mean-field study of dynamical susceptibilities in two-band Hubbard model. Varying the model parameters we analyze the two-particle excitations in the normal as well as in the ordered phase, an excitonic condensate. The two-particle DMFT spectra in the ordered phase reveal the gapless Goldstone modes arising from spontaneous breaking of continuous symmetries. We also observe gapped Higgs mode, characterized by vanishing of the gap at the phase boundary. Qualitative changes observed in the spin susceptibility can be used as an experimental probe to identify the excitonic condensation., Comment: published version

While key effects of the many-body problem---such as Kondo and Mott physics---can be understood in terms of on-site correlations, non-local fluctuations of charge, spin, and pairing amplitudes are at the heart of the most fascinating and unresolved phenomena in condensed matter physics. Here, we review recent progress in diagrammatic extensions to dynamical mean-field theory for ab initio materials calculations. We first recapitulate the quantum field theoretical background behind the two-particle vertex. Next we discuss latest algorithmic advances in quantum Monte Carlo simulations for calculating such two-particle quantities using worm sampling and vertex asymptotics, before giving an introduction to the ab initio dynamical vertex approximation (AbinitioD$\Gamma$A). Finally, we highlight the potential of AbinitioD$\Gamma$A by detailing results for the prototypical correlated metal SrVO$_3$., Comment: 8 pages, 8 figures; JPSJ Special Topics "New ab inito approaches to explore emergent phenomena in quantum matters"

Calculations show that battery can deliver up to 35 watt-hours per pound, conventional lead-acid batteries deliver 10 to 15 watt-hours per pound. Weight reduction is due to replacement of solid lead-peroxide electrodes with metal current-collector screen, catalyst, and Teflon membrane.

Housings development and circuit design and packaging technology for space related applications