Gap Symmetry an Thermal Conductivity in Nodal Superconductors

There are now many nodal superconductors in heavy fermion (HF) systems, charge conjugated organic metals, high Tc cuprates and ruthenates. On the other hand only few of them have a well established gap function. We present here a study of the angular dependent thermal conductivity in the vortex state of some of the nodal superconductors. We hope it will help to identify the nodal directions in the gap function of UPd_2Al_3, UNi_2Al_3, UBe_13 and URu_2Si_2.Comment: 4 pages, 5 figure

Nonlinear response and scaling law in the vortex state of d-wave superconductors

We study the field dependence of the quasi-particle density of states, the thermodynamics and the transport properties in the vortex state of d-wave superconductors when a magnetic field is applied perpendicular to the conducting plane, specially for the low field and the low temperature compared to the upper critical field and transition temperature, respectively, $H/H_{c2} \ll 1$ and $T/T_c \ll 1$. Both the superfluid density and the spin susceptibility exhibit the characteristic $\sqrt{H}$-field dependence, while the nuclear spin lattice relaxation rate T$_1^{-1}$ and the thermal conductivity are linear in field $H$. With increasing temperature, these quantities exhibit the scaling behavior in $T/\sqrt{H}$. The present theory applies to 2D $f$-wave superconductor as well; a possible candidate of the superconductivity in Sr$_2$RuO$_4$.Comment: 11 pages, 4 figure

Gap Symmetry and Thermal Conductivity in Nodal Superconductors

Here we consider the universal heat conduction and the angular dependent thermal conductivity in the vortex state for a few nodal superconductors. We present the thermal conductivity as a function of impurity concentration and the angular dependent thermal conductivity in a few nodal superconductors. This provides further insight in the gap symmetry of superconductivity in Sr$_2$RuO$_4$ and UPd$_2$Al$_3$.Comment: 2 pages, proceedings of SCES '0

Fulde-Ferrell-Larkin-Ovchinnikov state in d-wave superconductors

The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state can be found in layered d-wave superconductors such as high $T_c$ cuprates and $\kappa$-(ET)$_2$ salts in a planar magnetic field. We show the superconducting order parameter forms two dimensional crystalline lattice in the FFLO state for d-wave superconductors. Also the quasiparticle density of states and the thermodynamics of FFLO state are constructed. Therefore STM or NMR will provide a definitive test for the existence of the FFLO state.Comment: 5 pages including 2 figure

Thermal Conductivity in Vortex State of Nodal Superconductors

How to determine the symmetry of the superconducting order parameter is one of the important issues in novel superconductors, which include charge conjugated organic superconductors. We have proposed that the angular dependence of the thermal conductivity in a planar magnetic field provides a new window to look at the symmetry of the order parameter. After a brief summary of the quasiclassical approach we describe how the symmetry of the superconducting order parameter in Sr$_2$RuO$_4$, CeCoIn$_5$ and $\kappa$-(ET)$_2$Cu(NCS)$_2$ is determined. Also in some of experiments the phononic thermal conductivity plays the crucial role.Comment: 5 pages, 3 figures. to be published in Synthetic Metal

Paramagnetic state in d-wave Superconductors

We study theoretically the paramagnetic state in d-wave superconductors. We present the specific heat, the magnetization, superfluid density obtained within the weak-coupling model. At low temperatures and for small magnetic fields they exhibit simple power law behaviors, which should be accessible experimentally in hole-doped high-T_c cuprates and \kappa-(ET)_2 salts in a magnetic field within the conducting plane.Comment: 5 pages(EuroTeX), 13 figures, submitted to Europhysics Letter

Initial and Post-Initial Acquisition in the Serial Search Based Noncoherent Multiple Transmit/Receive Antenna Aided DS-CDMA Downlink

In this paper we investigate the issues of both initial and post-initial acquisition schemes in the multiple transmit/receive antenna aided DS-CDMA downlink, when communicating over uncorrelated Rayleigh channels. The associated Mean Acquisition Time (MAT) performance trends are characterised as a function of the number of transmit/receive antennas. Furthermore, we characterise both the initial and post-initial acquisition performance as a function of the relevant system parameters. It is demonstrated that in contrast to our expectations, the achievable MAT degrades at low Ec/Io values, except for the case of P = 2 transmit antennas operating in conjunction with R=1 receive antenna over the specific Signal-to-Interference plus Noise Ratio (SINR) per chip (Ec/Io) range considered, as the number of transmit antennas is increased. Ironically, our findings suggest that increasing the number of transmit antennas in a MIMO-aided CDMA system results in combining the low-energy, noise-contaminated signals of the transmit antennas, which ultimately increases the MAT by an order of magnitude, when the SINR is relatively low. This phenomenon has a detrimental effect on the performance of Rake receiver based synchronisation schemes, when the perfectly synchronised system is capable of attaining its target bit error rate performance at reduced SINR values, as a benefit of employing multiple transmit antennas. Therefore our future research will be focused on specifically designing acquisition schemes for MIMO systems

Differential Coherent Code Acquisition in the Multiple Transmit/Receive Antenna Aided DS-CDMA Downlink

In this contribution we investigate both differentially coherent and noncoherent code acquisition schemes in the multiple transmit/receive antenna aided DS-CDMA downlink, when communicating over uncorrelated Rayleigh channels. It is demonstrated that in contrast to our expectations, the achievable Mean Acquisition Time (MAT) degrades at low Ec/Io values, as the number of transmit antennas is increased in both differentially coherent and noncoherent code acquisition system scenarios, even though the degree of performance degradation depends upon the specific scheme considered. Ironically, our findings suggest that increasing the number of transmit antennas in a MIMO-aided CDMA system results in combining the low-energy, noise-contaminated signals of the transmit antennas, which ultimately increases the MAT by an order of magnitude, when the SINR is relatively low. Therefore our future research will be aimed at specifically designing acquisition schemes for MIMO systems

Analysis of Serial Search Based Code Acquisition in Multiple Transmit Antenna Aided DS-CDMA Downlink

In this contribution we investigate the serial search based initial code acquisition performance of DSCDMA employing multiple transmit antennas both with and without Post-Detection Integration (PDI), when communicating over uncorrelated Rayleigh channels. We characterise the associated performance trends as a function of the number of transmit antennas. It is demonstrated that in contrast to our expectation, the achievable correct detection probability PD degrades at low c o E /I values, as the number of transmit antennas is increased. It is extremely undesirable to degrade the achievable acquisition performance, when the system is capable of attaining its target bit error rate performance at reduced SINR values, as a benefit of employing multiple transmit antennas. Our future research will focus on the study of designing iterative turbo-like acquisition schemes designed for MIMO systems