Multiband Scenario Research Articles

Angular-dependent torque measurements onCeCoIn5single crystals

Angular dependent torque measurements were performed on single crystals of CeCoIn$_5$, a heavy fermion superconductor ($T_{c0}$ = 2.3 K), in the temperature, $T$, range 1.9 K $\leq T \leq $ 20 K and magnetic fields $H$ up to 14 T. A large paramagnetic effect is found in the normal state. Torque measurements in the mixed state were also performed. The torque curves show sharp hysteresis peaks at $\theta = 90^{o}$ ($\theta$ is the angle between $H$ and the $c-$axis of the crystal), a result of intrinsic pinning of vortices. The anisotropy $\gamma \equiv \sqrt{m_{c}/m_{a}}$ in the mixed state was determined from the reversible part of the vortex contribution to the torque signal using Kogan's model [Phys. Rev. B \textbf{38}, 7049 (1988)]. The anisotropy $\gamma$ decreases with increasing magnetic field and temperature. The fact that $\gamma$ is not a constant points towards a multiband scenario in this heavy fermion material.

Polarization diversity for multiband UWB systems

Ultra-wideband (UWB) transmission provides a fast local range wireless connection using the same frequency spectrum assigned to other narrowband communication standards. A precise knowledge of the indoor transmission channel is necessary to obtain high performance. Several channel models have been presented in the literature, but normally without considering the distortion effect caused by a real UWB antenna. A detailed antenna model shows that the radiation pattern varies with frequency, i.e., different receiver positions and antenna orientations result in different antenna frequency responses. In order to obtain a more uniform coverage over the indoor area, two transmitting antennas with orthogonal polarization can be used. The receiver can use a single antenna whose orientation and position is arbitrary within the coverage area, resulting in a special case of a 2:1 MISO system in which a space-time encoding is used at the transmitter. The target is to employ the polarization diversity to obtain a constant quality of symbol detection while the receiver moves around in the coverage area. The proposed polarization diversity scheme is applied in an UWB multiband scenario and it is compared to both a single antenna scheme and a classical space diversity scheme employing a single polarized antenna array.

Unpaired Electrons in the Heavy-Fermion SuperconductorCeCoIn5

Thermal conductivity and specific heat were measured in the superconducting state of the heavy-fermion material Ce(1-x)La(x)CoIn5. With increasing impurity concentration x, the suppression of T(c) is accompanied by the increase in residual electronic specific heat expected of a d-wave superconductor, but it occurs in parallel with a decrease in residual electronic thermal conductivity. This contrasting behavior reveals the presence of uncondensed electrons coexisting with nodal quasiparticles. An extreme multiband scenario is proposed, with a d-wave superconducting gap on the heavy-electron sheets of the Fermi surface and a negligible gap on the light, three-dimensional pockets.