Browsing by Author "Kokalj, Jure"

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    Charge transport in the Hubbard model at high temperatures: Triangular versus square lattice
    Vranić, Ana; Vučičević, Jakša; Kokalj, Jure; Skolimowski, Jan; Žitko, Rok; Mravlje, Jernej; Tanasković, Darko
    High-temperature bad-metal transport has been recently studied both theoretically and in experiments as one of the key signatures of strong electronic correlations. Here we use the dynamical mean field theory and its cluster extensions, as well as the finite-temperature Lanczos method to explore the influence of lattice frustration on the thermodynamic and transport properties of the Hubbard model at high temperatures. We consider the triangular and the square lattices at half-filling and at 15% hole doping. We find that for T greater than or similar to 1.5t the self-energy becomes practically local, while the finite-size effects become small at lattice size 4x4 for both lattice types and doping levels. The vertex corrections to optical conductivity, which are significant on the square lattice even at high temperatures, contribute less on the triangular lattice. We find approximately linear temperature dependence of dc resistivity in doped Mott insulator for both types of lattices.
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    Conductivity in the Square Lattice Hubbard Model at High Temperatures: Importance of Vertex Corrections
    Vučičević, Jakša; Kokalj, Jure; Žitko, Rok; Wentzell, Nils; Tanasković, Darko; Mravlje, Jernej
    Recent experiments on cold atoms in optical lattices allow for a quantitative comparison of the measurements to the conductivity calculations in the square lattice Hubbard model. However, the available calculations do not give consistent results, and the question of the exact solution for the conductivity in the Hubbard model remained open. In this Letter, we employ several complementary state-of-the-art numerical methods to disentangle various contributions to conductivity and identify the best available result to be compared to experiment. We find that, at relevant (high) temperatures, the self-energy is practically local, yet the vertex corrections remain rather important, contrary to expectations. The finite-size effects are small even at the lattice size 4×4, and the corresponding Lanczos diagonalization result is, therefore, close to the exact result in the thermodynamic limit.