An analysis of Luttinger's theorem shows that – contrary to recent claims – it is not valid for a generic Mott insulator. For a two-orbital Hubbard model with two electrons per site the crossover from a non-magnetic correlated insulating phase (Mott or Kondo insulator) to a band insulator is...

A method for estimating, via the Monte-Carlo simulation, the most often realized diffusion mechanisms in 2D ordered structures is presented. Taking as an example the diffusion of oxygen ions in 123 — YBCO high temperature superconductor we propose several diffusion mechanisms and show to what...

Ab initio total energy calculations have been performed for superconducting GdBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subsc ript> and insulating PrBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subsc ript> using the full-potential linear augmented plane-wave method in the local density approximation (LDA) and generalized gradient approximation (GGA). The comparison of the calculated...<//subsc></subscript></subscript></subscript><//subsc></subscript></subscript></subscript>

We have studied experimentally the electrical magneto-conductivity near the superconducting transition of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7-δ</Subs cript>, YBa<Subscript>2</Subscript> (Cu<Subscript>2.95</Subscript>Zn<Subscript>0.05</Subscript>)O<Subscript>7- δ</Subscript> and Y(Ba<Subscript>1.75</Subscript>Sr<Subscript>0.25</Subscript>)Cu<Subscript> 3</Subscript>O<Subscript>7-δ</Subscript> polycrystalline samples. The measurements were performed in magnetic fields ranging from 0 to 400 Oe applied parallel to...</subscript></subscript></subscript></subscript></subscript></subscript></subscript></subscript><//subs></subscript></subscript></subscript>