Thermal transport in granular metals

We study the electron thermal transport in granular metals at large tunnel conductance between the grains, $g_T \gg 1$ and not too low a temperature $T > g_T\delta$, where $\delta$ is the mean energy level spacing for a single grain. Taking into account the electron-electron interaction effects we calculate the thermal conductivity and show that the Wiedemann-Franz law is violated for granular metals. We find that interaction effects suppress the thermal conductivity less than the electrical conductivity.Comment: Replaced with published versio

ITO free OLEDs utilizing inkjet printed and low temperature plasma sintered Ag electrodes

We report an inkjet printed indium tin oxide ITO free electrode made from a particle free silver ink. After printing, an argon plasma is used to reduce the silver ions in the ink to metallic silver. This process does not require high temperatures and is therefore suitable for use with temperature sensitive substrates. Printed silver layers show good optical transmittance and electrical conductivity. To demonstrate the capabilities of the electrodes, inverted ITO free organic light emitting diodes OLEDs were produced via solution processing. In terms of luminance and efficacy, the devices containing the printed electrodes show improved luminance and current efficacy compared to ITO based reference devices. When fabricated with flexible substrates, the printed OLEDs show high bending stability, enabling flexible application

Effects of proximity to an electronic topological transition on normal state transport properties of the high-Tc superconductors

Within the time dependent Ginzburg-Landau theory, the effects of the superconducting fluctuations on the transport properties above the critical temperature are characterized by a non-zero imaginary part of the relaxation rate gamma of the order parameter. Here, we evaluate Im gamma for an anisotropic dispersion relation typical of the high-Tc cuprate superconductors (HTS), characterized by a proximity to an electronic topological transition (ETT). We find that Im gamma abruptly changes sign at the ETT as a function of doping, in agreement with the universal behavior of the HTS. We also find that an increase of the in-plane anisotropy, as is given by a non-zero value of the next-nearest to nearest hopping ratio r=t'/t, increases the value of | Im gamma | close to the ETT, as well as its singular behavior at low temperature, therefore enhancing the effect of superconducting fluctuations. Such a result is in qualitative agreement with the available data for the excess Hall conductivity for several cuprates and cuprate superlattices.Comment: to appear in Phys. Rev.

Magnetothermopower and Nernst effect in unconventional charge density waves

Recently we have shown that the striking angular dependent magnetoresistance in the low temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4 is consistently described in terms of unconventional charge density wave (UCDW). Here we investigate theoretically the thermoelectric power and the Nernst effect in UDW. The present results account consistently for the recent data of magnetothermopower in alpha-(BEDT-TTF)_2KHg(SCN)_4 obtained by Choi et al. (Phys. Rev. B, 65, 205119 (2002)). This confirms further our identification of LTP in this salt as UCDW. We propose also that the Nernst effect provides a clear signature of UDW.Comment: 4 pages, 4 figure