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Register a new userMicroscopic investigation of the weakly correlated noncentrosymmetric superconductor SrAuSi$_3$
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SrAuSi$_3$ is a noncentrosymmetric superconductor (NCS) with $T_c$ = 1.54 K, which to date has been studied only via macroscopic techniques. By combining nuclear magnetic resonance (NMR) and muon-spin rotation ($mu$SR) measurements we investigate both the normal and the superconducting phase of SrAuSi$_3$ at a local level. In the normal phase, our data indicate a standard metallic behavior with weak electron correlations and a Korringa constant $S_mathrm{exp} = 1.31 times 10^{-5}$ sK. The latter, twice the theoretical value, can be justified by the Moriya theory of exchange enhancement. In the superconducting phase, the material exhibits conventional BCS-type superconductivity with a weak-coupling s-wave pairing, a gap value $Delta(0)$ = 0.213(2) meV, and a magnetic penetration depth $lambda(0)$ = 398(2) nm. The experimental proof of weak correlations in SrAuSi$_{3}$ implies that correlation effects can be decoupled from those of antisymmetric spin-orbit coupling (ASOC), thus enabling accurate band-structure calculations in the weakly-correlated NCSs.
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The noncentrosymmetric superconductor Mo$_3$Rh$_2$N, with $T_c = 4.6$ K, adopts a $beta$-Mn-type structure (space group $P$4$_1$32), similar to that of Mo$_3$Al$_2$C. Its bulk superconductivity was characterized by magnetization and heat-capacity measurements, while its microscopic electronic properties were investigated by means of muon-spin rotation and relaxation ($mu$SR). The low-temperature superfluid density, measured via transverse-field (TF)-$mu$SR, evidences a fully-gapped superconducting state with $Delta_0 = 1.73 k_mathrm{B}T_c$, very close to 1.76 $k_mathrm{B}T_c$ - the BCS gap value for the weak coupling case, and a magnetic penetration depth $lambda_0 = 586$ nm. The absence of spontaneous magnetic fields below the onset of superconductivity, as determined by zero-field (ZF)-$mu$SR measurements, hints at a preserved time-reversal symmetry in the superconducting state. Both TF-and ZF-$mu$SR results evidence a spin-singlet pairing in Mo$_3$Rh$_2$N.
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The solid-solution SrRu$_{1-x}$Rh$_x$O$_3$ ($0le x le1$) is a variable-electron-configuration system forming in the nearly-cubic-perovskite basis, ranging from the ferromagnetic 4$d^4$ to the enhanced paramagnetic 4$d^5$. Polycrystalline single-phase samples were obtained over the whole composition range by a high-pressure-heating technique, followed by measurements of magnetic susceptibility, magnetization, specific heat, thermopower, and electrical resistivity. The ferromagnetic order in long range is gradually suppressed by the Rh substitution and vanishes at $x sim 0.6$. The electronic term of specific-heat shows unusual behavior near the critical Rh concentration; the feature does not match even qualitatively with what was reported for the related perovskites (Sr,Ca)RuO$_3$. Furthermore, another anomaly in the specific heat was observed at $x sim 0.9$.
The superconducting gap structure of a topological crystalline insulator (TCI) candidate ZrRuAs ($T^{rm on}_{rm c}$ = 7.9(1) K) with a noncentrosymmetric crystal structure has been investigated using muon spin rotation/relaxation ($mu$SR) measurements in transverse-field (TF) and zero-field (ZF) geometries. We also present the results of magnetization, electrical resistivity and heat capacity measurements on ZrRuAs, which reveal bulk superconductivity below 7.9~K. The temperature dependence of the effective penetration depth obtained from the analysis of the TF-$mu$SR spectra below $T_{rm c}$ is well described by an isotropic $s$-wave gap model as also inferred from an analysis of the heat capacity in the superconducting state. ZF $mu$SR data do not show any significant change in the muon spin relaxation rate above and below the superconducting transition temperature indicating that time-reversal symmetry is preserved in the superconducting state of this material.
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