A. V. Klaptsov

Nanoscale phase separation in manganites

We study the possibility of nanoscale phase separation in manganites in the framework of the double-exchange model. The homogeneous canted state of this model is proved to be unstable towards the formation of small ferromagnetic droplets inside an antiferromagnetic insulating matrix. For the ferromagnetic polaronic state we analyse the quantum effects related to the tails of electronic wave function and a possibility of electron hopping in the antiferromagnetic background. We find that these effects lead to the formation of the threshold for the polaronic state.

Characteristics of the phase-separated state in manganites: Relationship with transport and magnetic properties

The temperature and magnetic field dependence of the resistivity, magnetoresistance, and magnetic susceptibility of phase-separated manganites in the temperature range corresponding to nonmetallic behavior are considered within the framework of a model of inhomogeneous state with allowance for the existence of ferromagnetically correlated regions even in the absence of long-range magnetic order. The main attention is given to the interval of high temperatures and weak fields. The main characteristics of the phase-separated state of manganites are evaluated from a comparison of the theoretical results with available experimental data.

Composite Fermions and Quartets in Optical Traps and in High-Tc Superconductors

We consider a possibility of the creation of composite fermions in optical traps and in high‐Tc superconductors. For optical traps we study a model of Fermi‐Bose mixture with resonant attraction between particles of different sorts. In this case a pairing between fermion and boson of the type bf is possible. This pairing corresponds to creation of composite fermions. At low temperatures and equal densities of fermions and bosons composite fermions are further paired in quartets. In the 2D case we exactly solve Skorniakov‐Ter‐Martirosian type of integral equations and find the binding energies of two bosons plus one fermion fbb and two bosons plus two fermions fbfb. For high‐Tc superconductors we consider a quartet — a bound state of two composite holes Δ =〈 hh 〉, where each composite hole h = fb consists of a spinon and a holon bound by the stringlike potential. Our investigations are important for recent experiments on the observation of weakly bound composite fermions and bosons in optical traps in the ...

SPIN-DEPENDENT TRANSPORT IN PHASE-SEPARATED MANGANITES

Starting from the assumption that ferromagnetically correlated regions exist in manganites even in the absence of long-range magnetic order, we construct a model of charge transfer due to the spin-dependent tunnelling of charge carriers between such regions. This model allows us to analyze the temperature and magnetic field dependence of resistivity, magnetoresistance, and magnetic susceptibility of phase-separated manganites in the temperature range corresponding to non-metallic behavior. The comparison of theoretical and experimental results reveals the main characteristics of the phase-separated state.