An explicit matrix product ansatz is presented, in the first two orders in the (weak) coupling parameter, for the nonequilibrium steady state of the homogeneous, nearest neighbor Heisenberg XXZ spin 1/2 chain driven by Lindblad operators which act only at the edges of the chain. The first order of the density operator becomes in the thermodynamic limit an exact pseudolocal conservation law and yields via the Mazur inequality a rigorous lower bound on the high temperature spin Drude weight. Such a Mazur bound is found to be a nonvanishing fractal (nowhere smooth) function of the anisotropy parameter Delta for Delta(1.

COBISS.SI-ID: 2347108

We have developed a new, efficient numerical method for solving one and two holes in the antiferromagnetic background. We have explored the influence of two different polarizations of quantum oxygen vibrations on the spacial symmetry of the bound magnetic bipolaron in the context of the t−J model. Electron phonon coupling to transverse polarization stabilizes the bound bipolaron state with the d−wave symmetry. The existence of a magnetic background is essential for the formation of a d−wave bipolaron state.

COBISS.SI-ID: 2189924

Using a combination of numerical and analytical methods we have classified transport in the XXZ model for all values of the anisotropy. For large anisotropies the diffusion constant scales inversely with the anisotropy. At the isotropic point an anomalous transport is demnonstrated, being a first example of anomalous transport in a coherent quantum model.

COBISS.SI-ID: 2357860

Bad metals are materials with resistivity corresponding to the meanfreepath of charge carriers comparable to the nearest neighbour distance in the crystal lattice. Such behavior is found in some correlated materials, for instance in doped Mott insulators. Using the dynamical mean field theory we studied the doped Hubbard model and established the temperature dependence of the spectral properties. We discovered the existence of resilient quasiparticles that remain well defined above the Fermi temperature and dominate the transport in the intermediate regime up to the Mott-Ioffe-Regel regime.

COBISS.SI-ID: 26841383

We present a calculation of the recombination rate of the excited holon-doublon pairs based on the two-dimensional model relevant for undoped cuprates, which shows that fast processes, observed in pump-probe experiments on Mott-Hubbard insulators in the picosecond range, can be explained even quantitatively with the multimagnon emission. The precondition is the existence of the Mott-Hubbard bound exciton of the s-type. We find that its decay is exponentially dependent on the Mott-Hubbard gap and on the magnon energy, with a small prefactor, which can be traced back to strong correlations and consequently large exciton-magnon coupling.

COBISS.SI-ID: 2579044