Nonlinear response of a Mott insulator to external electric field, corresponding to dielectric breakdown phenomenon, is studied within a one-dimensional half-filled Hubbard model. Analytical and numerical results show that the threshold field dependence on the charge gap Delta is nontrivial, being proportional to Delta^{3/2}. Numerical results on small systems indicate on the persistence of a similar mechanism for the breakdown for decreasing magnetization.

COBISS.SI-ID: 2522468

We perform an accurate time-dependent numerical study of an out-of-equilibrium response of a bound state within t-J systems on a two-leg ladder and a square lattice. We show that the bound hole pair decays with the onset of finite steady current if both mechanisms for binding and the dissipation share matching degrees of freedom. Moreover, by investigating the mechanism of decay on the square lattice we find that the dynamics is governed by the decay in the direction perpendicular to the electric field, leading to much shorter decay times in comparison to the ladder where such dynamics is topologically restricted.

COBISS.SI-ID: 2492516

We discuss a combination of unitary and anti-unitary symmetry of quantum Liouvillian dynamics, in the context of open quantum systems, which implies a D2 symmetry of the complex Liouvillian spectrum. For sufficiently weak system-bath coupling it implies a uniform decay rate for all coherences, i.e., off-diagonal elements of the system's density matrix taken in the eigenbasis of the Hamiltonian. We then outline two general classes of examples of such PT-symmetric quantum Liouvillian dynamics of open many qubit systems, namely interacting hard-core bosons (or more general XYZ-type spin 1/2 systems) with, either (i) pure dephasing noise, or (ii) having solely single particle (or single spin) injection/absorption incoherent processes.

COBISS.SI-ID: 2458724

We have studied the transport properties of nanoscopic devices consisting of quantum dots with ferromagnetic leads. We have established the phase diagram of the system, in particular in the (p,t) plane, where p is the spin polarization in the leads, while t is the tunneling coupling (overlap integral) between the two dots. Out aim was to determine to what extent one can restore the broken symmetry due to induced local magnetic field in the dot using the exchange filed resulting from the superexchange inter-dot coupling. We determined that it is possible to vary the spin conductance using the electrostatic gates alone, and even to change the sign of the spin current.

COBISS.SI-ID: 25752871

We investigate the origin of the high Néel temperature recently found in Tc4+ perovskites. The electronic structure in the magnetic state of SrTcO3 and its 3d analogue SrMnO3 is calculated within a framework combining band-structure and many-body methods. In agreement with experiment, for SrTcO3 a smaller magnetic moment and 4 times larger Néel temperature are found. We show that this is because the Tc compound lies on the verge of the itinerant-to-localized transition, while the Mn compound lies deeper into the localized side. For SrTcO3 we predict that the Néel temperature depends weakly on applied pressure, in clear violation of Bloch’s rule, signaling the complete breakdown of the localized picture.

COBISS.SI-ID: 26399271