Measurements of the temperature dependence of the electrical resistivity and the Hall effect in epitaxial films of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ are reported. The resistivity is close to linear in T and the cotangent of the Hall angle proportional to ${\mathit{T}}^2$ at temperatures sufficiently above ${\mathit{T}}_{\mathit{c}}$. Deviations from this behavior near ${\mathit{T}}_{\mathit{c}}$ are attributed to thermodynamic fluctuations and are analyzed in terms of theories for direct (Aslamazov-Larkin) and indirect (Maki-Thompson) fluctuation contributions in a layered superconductor. We obtain an unequivocal fit to both paraconductivity and excess-Hall-effect data with a consistent set of three parameters, i.e., the c-axis coherence length ${\xi }_{\mathit{c}}$(0)=1.5 Å, the phase-relaxation time ${\mathrm{\tau }}_{\mathrm{\phi }}$=8.6×${10}^{\mathrm{-}14}$ s at 100 K, and the electron-hole asymmetry parameter β=-0.17. We observe a sign change of the excess Hall effect close to ${\mathit{T}}_{\mathit{c}}$, when the Aslamazov-Larkin process becomes dominant.

We present a study of Nernst effect in underdoped ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ in magnetic fields as high as 28 T. At high fields, a sizable Nernst signal was found to persist in the presence of a field-induced nonmetallic resistivity. By simultaneously measuring resistivity and the Nernst coefficient, we extract the entropy of vortex cores in the vicinity of this field-induced superconductor-insulator transition. Moreover, the temperature dependence of the thermoelectric Hall angle provides strong constraints on the possible origins of the finite Nernst signal above $T_c$, as recently discovered by Xu et al. [Nature (London) 406, 486 (2000)].

Coordination polymerization leads to various metal–organic frameworks (MOFs) with unique physical properties and chemical functionalities. One of the challenges towards their applications as porous materials is to make MOFs optimally conductive to be used as electronic components. Here, it is demonstrated that Co-MOF-74, a honeycomb nano–framework with one–dimensionally arranged cobalt atoms, advances its physical properties by accommodating tetracyanochinodimethan (TCNQ), an acceptor molecule. Strong intermolecular charge transfer reduces the optical band gap down to 1.5 eV of divalent TCNQ and enhances the electrical conduction, which allows the MOF to be utilized for resistive gas- and photo-sensing. The results provide insight into the electronic interactions in doped MOFs and pave the way for their electronic applications.

${\mathrm{La}}_{\text{1−x}}{\mathrm{Li}}_x{\mathrm{MnO}}_{\mathrm{3}}$ ($\text{x=0,}$ 0.1, 0.2, and 0.3) were synthesized by using conventional solid state reaction and partial melting technique. The compounds were determined to be of rhombohedral structure by x-ray powder diffraction. For the $\text{x=0.2}$ and $\text{x=0.3}$ samples, room temperature neutron powder diffraction patterns were collected and analyzed with the Rietveld method. The analysis showed that the Li substitutes onto the La site in the rhombohedral perovskite lattice. Resistivities were measured between 4.2 K and room temperature in the magnetic fields of 0, 1, 2, 4, 8, and 13 T. A wide semiconductor-metal transition at temperatures between 160 and 210 K or between 200–230 K were observed for both samples with $\text{x=0.2}$ and 0.3, respectively. Large magnetoresistances above 20%–80% were achieved at fields from null to 13 T over a wide temperature range from the ferromagnetic transitions down to 4.2 K. However, the $\text{x=0}$ and 0.1 samples show a semiconducting behavior in resistivity measured between 77 and 300 K.

A detailed study of normal-state magnetotransport properties in (Bi,Pb${)}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{x}}$ thin films with a zero-resistance critical temperature ${\mathit{T}}_{\mathit{c}0}$=105 K prepared by dc-magnetron sputtering on MgO substrates is reported. Measurements of the electrical resistivity, the magnetoresistance, and the Hall effect are analyzed with regard to contributions of the superconducting order-parameter thermodynamic fluctuations, using theories for two-dimensional, layered superconductors. We have obtained a consistent set of parameters, i.e., the in-plane coherence length ${\xi }_{\mathit{a}\mathit{b}}$(0)=1.6 nm, the out-of-plane coherence length ${\xi }_{\mathit{c}}$(0)=0.14 nm, and the electron-hole asymmetry parameter β=-0.38. At temperatures below 118 K, we observe a remarkable enhancement (above theoretical predictions) of both the excess Hall effect and magnetoconductivity, whereas no such effect is detected for the zero-field paraconductivity. The above anomalies are attributed to a nonuniform critical temperature distribution inside our samples and can be well explained assuming a Gaussian distribution of ${\mathit{T}}_{\mathit{c}}$’s with a standard deviation δ${\mathit{T}}_{\mathit{c}}$=2.3 K. The excess Hall effect caused by superconducting fluctuations is negative in the entire accessible temperature range, which indicates, together with the paraconductivity and magnetoconductivity results that the indirect (Maki-Thompson) fluctuation process for (Bi,Pb${)}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{x}}$ is vanishingly small at temperatures from ${\mathit{T}}_{\mathit{c}}$ to 130 K.