Studies of superconductivity in multiband correlated electronic systems has become one of the central topics in condensed matter/materials physics. In this paper, we present the results of thermodynamic measurements on the superconducting filled skutterudite system Pr1−xCexPt4Ge12 (0 ≤ x ≤ 0.2) to investigate how substitution of Ce at Pr sites affects superconductivity. We find that an increase in Ce concentration leads to a suppression of the superconducting transition temperature from Tc ∼ 7.9 K for x = 0 to Tc ∼ 0.6 K for x = 0.14. Our analysis of the specific heat data for x ≤ 0.07 reveals that superconductivity must develop in at least two bands: the superconducting order parameter has nodes on one Fermi pocket and remains fully gapped on the other. Both the nodal and nodeless gap values decrease, with the nodal gap being suppressed more strongly, with Ce substitution. Ultimately, the higher Ce concentration samples (x > 0.07) display a nodeless gap only.

The superconducting and normal-state properties of the filled-skutterudite system Pr1−xEuxPt4Ge12 were studied. Polycrystalline samples were investigated via x-ray diffraction, electrical resistivity, magnetic susceptibility, and specific heat measurements. Upon Eu substitution, we observed a crossover from superconducting to antiferromagnetic states with a region where both states coexist. In the superconducting region, the specific heat data exhibit a change of temperature dependence, suggesting an evolution from a nodal to a nodeless superconducting energy gap or a suppression of multiband superconductivity. This change is relatively slower than those reported for different substituent ions, suggesting paramagnetic impurities have a weaker pair breaking effect on unconventional superconductivity in PrPt4Ge12. In the normal state, an evolution from Fermi-liquid to non-Fermi-liquid behavior was observed, accompanied by the coexistence of superconductivity and antiferromagnetism, suggesting the underlying electronic structure is primarily responsible for the complex physical phenomena found in this system.

By performing a series of thermodynamic measurements in an applied magnetic field Hext, we investigated the effects of Eu substitution on the Pr sites in filled skutterudite compound Pr1−xEuxPt4Ge12 (0 ≤ x ≤ 1). A heat capacity Schottky anomaly is present over the whole doping range. For the samples with x > 0.5, the temperature of the maximum Tmax shifts to lower temperature with increasing Hext. We argue that this behavior reflects the antiferromagnetic (AFM) ordering of the Eu moments, as the AFM transition is suppressed by Hext. The Schottky anomaly in the samples with x ≤ 0.5 shift to higher temperatures with increasing magnetic field, signaling the presence of an internal magnetic field due to short-range AFM correlations induced by magnetic moments of neighboring Eu sites. In low Hext, the Schottky gaps show a non-linear relationship with Hext as the magnetic moments become weakly magnetized. In high Hext, the magnetic moments of Eu sites become completely aligned with Hext. Thus, increasing Hext does not further increase the magnetization, hence the Schottky gaps increase linearly with Hext.

Motivated by current research efforts towards exploring the interplay between magnetism and superconductivity in multiband electronic systems, we have investigated the effects of Eu substitution through thermodynamic measurements on the superconducting filled skutterudite alloys Pr1−xEuxPt4Ge12. An increase in Eu concentration leads to a suppression of the superconducting transition temperature consistent with an increase of magnetic entropy due to Eu local moments. While the low-temperature heat capacity anomaly is present over the whole doping range, we find that in alloys with x ≤ 0.5 the Schottky peaks in the heat capacity in the superconducting state appear to be due to Zeeman splitting by an internal magnetic field. Our theoretical modeling suggests that this field is a result of the short-range antiferromagnetic correlations between the europium ions. For the samples with x > 0.5, the peaks in the heat capacity signal the onset of antiferromagnetic (AFM) ordering of the Eu moments.

We report electrical resistivity, magnetization, and specific heat measurements on the correlated electron system Ce1−xSmxCoIn5 (0 ≤ x ≤ 1). Superconductivity (SC) in the heavy fermion compound CeCoIn5, which is suppressed with increasing Sm concentration x, and antiferromagnetic (AFM) order of SmCoIn5, which is suppressed with decreasing x, converge near a quantum critical point at xQCP ≈ 0.15, with no indication of coexistence of SC and AFM in the vicinity of the QCP. Non-Fermi liquid (NFL) behavior is observed in the normal state electrical resistivity, ρ(T), and specific heat, C(T), in the vicinity of the QCP; e.g., the coefficient and the exponent of the powerlaw T-dependence of ρ(T) exhibit pronounced maxima and minima, respectively, at xQCP, while C(T)/T exhibits a logarithmic divergence in T at xQCP. A low-temperature upturn in ρ(T) develops in the range 0.70 ≤ x ≤ 0.85 which is reminiscent of a single impurity Kondo effect, suggesting that Sm substitution tunes the relative strength of competing Kondo and Ruderman-Kittel-Kasuya-Yosida (RKKY) energy scales. The suppression of SC with increasing x is probably associated with the exchange interaction between the Ce quasiparticles involved in the superconductivity and the magnetic moments of the Sm ions.