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

High-pressure study of non-Fermi liquid and spin-glass-like behavior in CeRhSn

We present measurements of the temperature dependence of electrical resistivity of CeRhSn up to ~ 27 kbar. At low temperatures, the electrical resistivity varies linearly with temperature for all pressures, indicating non-Fermi liquid behavior. Below a temperature Tf ~ 6 K, the electrical resistivity deviates from a linear dependence. We found that the low-temperature feature centered at T = Tf shows a pressure dependence dTf/dP ~ 30 mK/kbar which is typical of canonical spin glasses. This interplay between spin-glass-like and non-Fermi liquid behavior was observed in both CeRhSn and a Ce0.9La0.1RhSn alloy.Comment: 5 pages, 3 figures, accepted for publication to Journal of Physics: Condensed Matte

Pressure-induced enhancement of superconductivity and suppression of semiconducting behavior in Ln(O0.5F0.5)BiS2 (Ln = La, Ce) compounds

Electrical resistivity measurements as a function of temperature between 1 K and 300 K were performed at various pressures up to 3 GPa on the superconducting layered compounds Ln(O0.5F0.5)BiS2 (Ln = La, Ce). At atmospheric pressure, La(O0.5F0.5)BiS2 and Ce(O0.5F0.5)BiS2 have superconducting critical temperatures, Tc, of 3.3 K and 2.3 K, respectively. For both compounds, the superconducting critical temperature Tc initially increases, reaches a maximum value of 10.1 K for La(O0.5F0.5)BiS2 and 6.7 K for CeO(0.5F0.5)BiS2, and then gradually decreases with increasing pressure. Both samples also exhibit transient behavior in the region between the lower Tc phase near atmospheric pressure and the higher Tc phase. This region is characterized by a broadening of the superconducting transition, in which Tc and the transition width, delta Tc, are reversible with increasing and decreasing pressure. There is also an appreciable pressure-induced and hysteretic suppression of semiconducting behavior up to the pressure at which the maximum value of Tc is found. At pressures above the value at which the maximum in Tc occurs, there is a gradual decrease of Tc and further suppression of the semiconducting behavior with pressure, both of which are reversible.Comment: 9 pages, 6 figures. Phys. Rev. B accepte

Superconductivity, magnetic order, and quadrupolar order in the filled skutterudite system Pr1−x_{1-x}Ndx_{x}Os4_4Sb12_{12}

Superconductivity, magnetic order, and quadrupolar order have been investigated in the filled skutterudite system Pr$_{1-x}$Nd$_{x}$Os$_4$Sb$_{12}$ as a function of composition $x$ in magnetic fields up to 9 tesla and at temperatures between 50 mK and 10 K. Electrical resistivity measurements indicate that the high field ordered phase (HFOP), which has been identified with antiferroquadruoplar order, persists to $x$ $\sim$ 0.5. The superconducting critical temperature $T_c$ of PrOs$_4$Sb$_{12}$ is depressed linearly with Nd concentration to $x$ $\sim$ 0.55, whereas the Curie temperature $T_{FM}$ of NdOs$_4$Sb$_{12}$ is depressed linearly with Pr composition to ($1-x$) $\sim$ 0.45. In the superconducting region, the upper critical field $H_{c2}(x,0)$ is depressed quadratically with $x$ in the range 0 $<$ $x$ $\lesssim$ 0.3, exhibits a kink at $x$ $\approx$ 0.3, and then decreases linearly with $x$ in the range 0.3 $\lesssim$ $x$ $\lesssim$ 0.6. The behavior of $H_{c2}(x,0)$ appears to be due to pair breaking caused by the applied magnetic field and the exhange field associated with the polarization of the Nd magnetic moments, in the superconducting state. From magnetic susceptibility measurements, the correlations between the Nd moments in the superconducting state appear to change from ferromagnetic in the range 0.3 $\lesssim$ $x$ $\lesssim$ 0.6 to antiferromagnetic in the range 0 $<$ $x$ $\lesssim$ 0.3. Specific heat measurements on a sample with $x$ $=$ 0.45 indicate that magnetic order occurs in the superconducting state, as is also inferred from the depression of $H_{c2}(x,0)$ with $x$.Comment: 7 pages, 7 figures, currently submitted to Phys. Rev.