We report a strategy to induce superconductivity in the BiS\(_2\)-based compound LaOBiS\(_2\). Instead of substituting F for O, we increase the charge-carrier density (electron dope) via substitution ...of tetravalent Th\(^{+4}\), Hf\(^{+4}\), Zr\(^{+4}\), and Ti\(^{+4}\) for trivalent La\(^{+3}\). It is found that both the LaOBiS\(_2\) and ThOBiS\(_2\) parent compounds are bad metals and that superconductivity is induced by electron doping with \emph{T\(_c\)} values of up to 2.85 K. The superconducting and normal states were characterized by electrical resistivity, magnetic susceptibility, and heat capacity measurements. We also demonstrate that reducing the charge-carrier density (hole doping) via substitution of divalent Sr\(^{+2}\) for La\(^{+3}\) does not induce superconductivity.
We report measurements of electrical resistivity, magnetic susceptibility, specific heat, and thermoelectric power on the system Pr1-xCexPt4Ge12. Superconductivity is suppressed with increasing Ce ...concentration up to x = 0.5, above which there is no evidence for superconductivity down to 1.1 K. The Sommerfeld coefficient {\gamma} increases with increasing x from 48 mJ/mol K^2 up to 120 mJ/mol K^2 at x = 0.5, indicating an increase in strength of electronic correlations. The temperature dependence of the specific heat at low temperatures evolves from roughly T^3 for x = 0 to e^(-\Delta /T) behavior for x = 0.05 and above, suggesting a crossover from a nodal to a nodeless superconducting energy gap or a transition from multiband to single-band superconductivity. Fermi-liquid behavior is observed throughout the series in low-temperature magnetization, specific heat, and electrical resistivity measurements.
We report results of zero-field muon spin relaxation experiments on the filled-skutterudite superconductors Pr sub(1-x) Ce sub(x) Pt sub(4) Ge sub(12), x = 0, 0.07, 0.1, and 0.2, to investigate the ...effect of Ce doping on broken time-reversal symmetry (TRS) in the superconducting state. In these alloys broken TRS is signaled by the onset of a spontaneous static local magnetic field B sub(s) below the superconducting transition temperature. We find that B sub(s) decreases linearly with x and arrow right 0 at x asymptotically = 0.4, close to the concentration above which superconductivity is no longer observed. The (Pr,Ce)Pt sub(4) Ge sub(12) and isostructural (Pr,La)Os sub(4) Sb sub(12) alloy series both exhibit superconductivity with broken TRS, and in both the decrease of B sub(s) is proportional to the decrease of Pr concentration. This suggests that Pr-Pr intersite interactions are responsible for the broken TRS. The two alloy series differ in that the La-doped alloys are superconducting for all La concentrations, suggesting that in (Pr,Ce)Pt sub(4) Ge sub(12) pair-breaking by Ce doping suppresses superconductivity. For all x the dynamic muon spin relaxation rate decreases somewhat in the superconducting state. This may be due to Korringa relaxation by conduction electrons, which is reduced by the opening of the superconducting energy gap.
CeOs$_4$Sb$_{12}$, a member of the skutterudite family, has an unusual
semimetallic low-temperature $\cal{L}$-phase that inhabits a wedge-like area of
the field $H$ - temperature $T$ phase diagram. ...We have conducted measurements
of electrical transport and megahertz conductivity on CeOs$_4$Sb$_{12}$ single
crystals under pressures of up to 3 GPa and in high magnetic fields of up to 41
T to investigate the influence of pressure on the different $H$-$T$ phase
boundaries. While the high-temperature valence transition between the metallic
$\cal{H}$-phase and the $\cal{L}$-phase is shifted to higher $T$ by pressures
of the order of 1 GPa, we observed only a marginal suppression of the
$\cal{S}$-phase that is found below 1 K for pressures of up to 1.91 GPa.
High-field quantum oscillations have been observed for pressures up to 3.0 GPa
and the Fermi surface of the high-field side of the $\cal{H}$-phase is found to
show a surprising decrease in size with increasing pressure, implying a change
in electronic structure rather than a mere contraction of lattice parameters.
We evaluate the field-dependence of the effective masses for different
pressures and also reflect on the sample dependence of some of the properties
of CeOs$_4$Sb$_{12}$ which appears to be limited to the low-field region.
We report results of a muon spin rotation and relaxation (\(\mu\)SR) study of dilute Pd\(_{1-x}\)Ni\(_x\) alloys, with emphasis on Ni concentrations \(x =\) 0.0243 and 0.025. These are close to the ...critical value \(x_\mathrm{cr}\) for the onset of ferromagnetic long-range order (LRO), which is a candidate for a quantum critical point. The 2.43 and 2.5 at.% Ni alloys exhibit similar \(\mu\)SR properties. Both samples are fully magnetic, with average muon local fields \(\langle B^\mathrm{loc}\rangle =\) 2.0 and 3.8 mT and Curie temperatures \(T_C =\) 1.0 and 2.03 K for 2.43 and 2.5 at.% Ni, respectively, at \(T = 0\). The temperature dependence of \(\langle B^\mathrm{loc}\rangle\) suggests ordering of Ni spin clusters rather than isolated spins. Just above \(T_C\) a two-phase region is found with separate volume fractions of quasistatic short-range order (SRO) and paramagnetism. The SRO fraction decreases to zero with increasing temperature a few kelvin above \(T_C\). This mixture of SRO and paramagnetism is consistent with the notion of an inhomogeneous alloy with Ni clustering. The measured values of \(T_C\) extrapolate to \(x_\mathrm{cr}\) = 0.0236 \(\pm\) 0.0027. The dynamic muon spin relaxation in the vicinity of \(T_C\) differs for the two samples: a relaxation-rate maximum at \(T_C\) is observed for \(x\) = 0.0243, reminiscent of critical slowing down, whereas for \(x =\) 0.025 no dynamic relaxation is observed within the \(\mu\)SR time window. The data suggest a mean-field-like transition in this alloy.
We investigated the onset of the many-body coherence in the f-orbital single crystalline alloys Ce(1-x)Yb(x)CoIn5 through thermodynamic and magneto-transport measurements. Our study shows the ...evolution of the many-body electronic state as the Kondo lattice of Ce moments is transformed into an array of Ce impurities. Specifically, we observe a smooth crossover from the predominantly localized Ce moment regime to the predominantly itinerant Yb f-electronic states regime for about 50% of Yb doping. Our analysis of the residual resistivity data unveils the presence of correlations between Yb ions, while from our analysis of specific heat data we conclude that for 0.65<x<0.775, ytterbium f-electrons strongly interact with the conduction electrons while the Ce moments remain completely decoupled. The sub-linear temperature dependence of resistivity across the whole range of Yb concentrations suggest the presence of a nontrivial scattering mechanism for the conduction electrons.
PDF
