Sergei A. Sergeenkov

A sharp decrease of resistivity in La0.7Ca0.3Mn0.96Cu0.04O3: Evidence for Cu-assisted coherent tunneling of spin polarons

Nearly a 50% decrease of resistivity \rho (T,x) due to just 4% Cu doping on the Mn site of La(2/3)Ca(1/3)Mn(1-x)Cu(x)O(3) is observed. Attributing the observed phenomenon to the substitution induced decrease of the spin polaron energy E_s(x) below the Curie point T_C(x)=T_C(0)(1-x), all data are found to be well fitted by the nonthermal coherent tunneling expression \rho (T,x) = \rho_0*exp(-\gamma M^2(T,x)) assuming M(T,x)=M_R(x)+M_0(x)*tanh{\sqrt{[T_C(x)/T]^2-1}} for the magnetization in the ferromagnetic state. The best fits through all the data points yield M_0(x)= \sqrt(1-x)M_0(0), M_R(x)=\sqrt(x)M_0(0), and E_s(x)=E_s(0)(1-x)^4 for the Cu induced modifications of the Mn spins dominated zero-temperature spontaneous magnetization, the residual paramagnetic contribution, and spin-polaron energy, respectively, with E_s(0)=0.12 eV.AbstractNearly a 50% decrease of the resistivity ρ(T, x) is observed upon just 4% Cu doping at the Mn site of La2/3Ca1/3Mn1−xCuxO3. When the observed phenomenon is attributed to a decrease of the spin-polaron energy Eσ(x) below TC(x), all of the data are found to be well fitted by the nonthermal coherent tunneling expression

Nonequilibrium behaviour and nonergodicity of high-Tc superconductive glass model

\rho (T,x) = \rho _0 e^{ - \gamma M^2 (T,x)}

Anomalous temperature behavior of the resistivity in lightly doped manganites around a metal-insulator phase transition

, assuming that the magnetization in the ferromagnetic state is given by the expression

Diamagnetic correlations of the superconductive glass model

M(T,x) = M_R (x) + M_0 (x)\tanh \left\{ {\sqrt {\left[ {T_C (x)/T} \right]^2 - 1} } \right\}

Irreversibility line and low-field grain-boundary pinning in electron-doped superconducting thin films

. The best fits through all the data points suggest