arXiv subjects

X. J. Chen

Publications and source records attributed to X. J. Chen.

40 records · Page 3Linked to original sources

arXiv2003

Small-polaron hopping conductivity in bilayer manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$

We report anisotropic resistivity measurements on a La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ single crystal over a temperature $T$ range from 2 to 400 K and in magnetic fields $H$ up to 14 T. For $T\geq 218$ K, the temperature dependence of the zero-field in-plane $ρ_{ab}(T)$ resistivity obeys the adiabatic small polaron hopping mechanism, while the out-of-plane $ρ_{c}(T)$ resistivity can be ascribed by an Arrhenius law with the same activation energy. Considering the magnetic character of the polarons and the close correlation between the resistivity and magnetization, we developed a model which allows the determination of $ρ_{ab,c}(H,T)$. The excellent agreement of the calculations with the measurements indicates that small polarons play an essential role in the electrical transport properties in the paramagnetic phase of bilayer manganites.

cond-mat.str-el↗

arXiv2002

Low-temperature electrical transport in bilayer manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$

The temperature $T$ and magnetic field $H$ dependence of anisotropic in-plane $ρ_{ab}$ and out-of-plane $ρ_{c}$ resistivities have been investigated in single crystals of the bilayer manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$. Below the Curie transition temperature $T_c=$ 125 K, $ρ_{ab}$ and $ρ_{c}$ display almost the same temperature dependence with an up-turn around 50 K. In the metallic regime (50 K $\leq T \leq$ 110 K), both $ρ_{ab}(T)$ and $ρ_{c}(T)$ follow a $T^{9/2}$ dependence, consistent with the two-magnon scattering. We found that the value of the proportionality coefficient $B_{ab}^{fit}$ and the ratio of the exchange interaction $J_{ab}/J_c$ obtained by fitting the data are in excellent agreement with the calculated $B_{ab}$ based on the two-magnon model and $J_{ab}/J_c$ deduced from neutron scattering, respectively. This provides further support for this scattering mechanism. At even lower $T$, in the non-metallic regime ($T<$ 50 K), {\it both} the in-plane $σ_{ab}$ and out-of-plane $σ_{c}$ conductivities obey a $T^{1/2}$ dependence, consistent with weak localization effects. Hence, this demonstrates the three-dimensional metallic nature of the bilayer manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ at $T<T_c$.

cond-mat.mtrl-sci↗

arXiv2002

Effects of pressure on the superconducting properties of magnesium diboride

We discuss the effects of hydrostatic pressure on the superconducting properties of MgB$_{2}$ within the framework of Eliashberg theory. By considering the pressure dependences of all parameters appearing in the McMillan formula, we show that the calculated pressure derivative of $T_{c}$ as well as the variation of $T_{c}$ with pressure are in good agreement with recent measurements. The pressure dependences of the energy gap $Δ_{0}$, the effective interaction strength $N(E_{F})v$, the critical magnetic field $H_{c}(0)$, and the electronic specific heat coefficient $γ$ are also predicted for this system. A comparison of pressure effect in non-transition elements clearly suggests that MgB$_{2}$ is an electron-phonon mediated superconductor.

cond-mat.supr-con↗

arXiv2002

Strain effect on electronic transport and ferromagnetic transition temperature in La$_{0.9}$Sr$_{0.1}$MnO$_{3}$ thin films

We report on a systematic study of strain effects on the transport properties and the ferromagnetic transition temperature $T_{c}$ of high-quality La$_{0.9}$Sr$_{0.1}$MnO$_{3}$ thin films epitaxially grown on (100) SrTiO$_{3}$ substrates. Both the magnetization and the resistivity are critically dependent on the film thickness. $T_{c}$ is enhanced with decreasing the film thickness due to the compressive stain produced by lattice mismatch. The resistivity above 165 K of the films with various thicknesses is consistent with small polaronic hopping conductivity. The polaronic formation energy $E_{P}$ is reduced with the decrease of film thickness. We found that the strain dependence of $T_{c}$ mainly results from the strain-induced electron-phonon coupling. The strain effect on $E_{P}$ is in good agreement with the theoretical predictions.

cond-mat.mtrl-sci↗