Evolution of crystalline electric field effects, superconductivity, and heavy fermion behavior in the specific heat of Pr(Os1−x_{1-x}Rux_x)4_4Sb12_{12}

Specific heat $C(T)$ measurements were made on single crystals of the superconducting filled skutterudite series Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$ down to 0.6 K. Crystalline electric field fits in the normal state produced parameters which were in agreement with previous measurements. Bulk superconductivity was observed for all values of the Ru concentration $x$ with transition temperatures consistent with previous experiments, confirming a minimum in $T_{c}$ at $x=0.6$. The $C(T)$ data below $T_{c}$ appear to be more consistent with power law behavior for $x=0$ (PrOs$_4$Sb$_{12}$), and with exponential behavior for $0.05 \leq x \leq 0.2$. An enhanced electronic specific heat coefficient $\gamma$ was observed for $x \leq 0.4$, further supporting $x \simeq 0.6$ as a critical concentration where the physical properties abruptly change. Significant enhancement of $\Delta C/T_{c}$ above the weak coupling value was only observed for $x=0$ and $x=0.05$.Comment: 16 pages, 5 figures, submitted to Physical Review B. v2: text added and figures modifie

Impurity induced density of states and residual transport in nonunitary superconductors

We obtain general expressions for the residual density of states, electrical conductivity and thermal conductivity for non-unitary superconductors due to impurity scattering. We apply the results to the so-called `B phase' of PrOs4Sb12, which we describe using a non-unitary gap function derived from symmetry considerations. The conductivity tensor has inequivalent diagonal components due to off-axis nodal positions which may be detectable in experiments.Comment: 8 pages, 1 figur

Anomalous Paramagnetic Magnetization in Mixed State of CeCoIn5_5 single crystals

Magnetization and torque measurements were performed on CeCoIn$_5$ single crystals to study the mixed-state thermodynamics. These measurements allow the determination of both paramagnetic and vortex responses in the mixed-state magnetization. The paramagnetic magnetization is suppressed in the mixed state with the spin susceptibility increasing with increasing magnetic field. The dependence of spin susceptibility on magnetic field is due to the fact that heavy electrons contribute both to superconductivity and paramagnetism and a large Zeeman effect exists in this system. No anomaly in the vortex response was found within the investigated temperature and field range

Pairing Symmetry of CeCoIn5_5 Detected by In-plane Torque Measurements

In-plane torque measurements were performed on heavy fermion CeCoIn$_5$ single crystals in the temperature $T$ range 1.8 K $\leq T \leq 10$ K and applied magnetic field $H$ up to 14 T. The normal-state torque is given by $\tau_n \propto H^4(1+T/T_K)^{-1}\sin 4\phi$. The reversible part of the mixed-state torque, obtained after subtracting the corresponding normal state torque, shows also a four-fold symmetry. In addition, sharp peaks are present in the irreversible torque at angles of $\pi/$4, 3$\pi$/4, 5$\pi$/4, 7$\pi$/4, etc. Both the four-fold symmetry in the reversible torque and the sharp peaks in the irreversible torque of the mixed state imply $d_{xy}$ symmetry of the superconducting order parameter. The field and temperature dependences of the reversible mixed-state torque provide further evidence for $d_{xy}$ wave symmetry. The four-fold symmetry in the normal state has a different origin since it has different field and temperature dependences than the one in the mixed state. The possible reasons of the normal state four-fold symmetry are discussed

Crystalline electric field effects in the electrical resistivity of PrOs4_4Sb12_{12}

The temperature $T$ and magnetic field $H$ dependencies of the electrical resistivity $\rho$ of the recently discovered heavy fermion superconductor \PrOsSb{} have features that are associated with the splitting of the Pr$^{3+}$ Hund's rule multiplet by the crystalline electric field (CEF). These features are apparently due to magnetic exchange and aspherical Coulomb scattering from the thermally populated CEF-split Pr$^{3+}$ energy levels. The $\rho(T)$ data in zero magnetic field can be described well by calculations based on CEF theory for various ratios of magnetic exchange and aspherical Coulomb scattering, and yield CEF parameters that are qualitatively consistent with those previously derived from magnetic susceptibility, specific heat, and inelastic neutron scattering measurements. Calculated $\rho(H)$ isotherms for a $\Gamma_{3}$ ground state qualitatively account for the `dome-shaped' feature in the measured $\rho(H)$ isotherms.Comment: 8 pages, 2 figures, submitted to Journal of Physics: Condensed Matte