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Register a new userSuperconducting gap symmetry of the noncentrosymmetric superconductor W3Al2C
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A detailed zero-field and transverse-field muon spin relaxation/rotation ($mu$SR) experiemnts have been carried out on the recently discovered non-centrosymmetric superconductor W$_3$Al$_2$C to speculate about its superconducting ground state. Bulk nature of superconductivity below 7.6 K is confirmed through magnetization measurements. No change in the $mu$SR spectra collected above and below $T_c$ is visible, ruling out the possibility of spontaneous magnetic field below $T_c$. This confirms that time-reversal symmetry is preserved for W$_3$Al$_2$C upon entering in the superconducting ground state. Temperature dependent superfluid density [$rho_s(T)$], which directly reflects the superconducting gap symmetry is obtained by the analysis of spectra obtained from the transverse-field $mu$SR experiments. Despite a non-centrosymmetric structure, W$_3$Al$_2$C adopts a fully gaped spin-singlet superconducting ground state with a zero temperature value of gap $Delta_0$ = 1.158(8) meV with gap-to-$T_c$ ratio 2$Delta_0/k_BT_capprox$3.54, classifying this material as a weakly-coupled superconductors.
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The superconducting gap structure of a topological crystalline insulator (TCI) candidate ZrRuAs ($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.
The superconducting gap structure of recently discovered heavy fermion CePt_3Si without spatial inversion symmetry was investigated by thermal transport measurements down to 40 mK. In zero field a residual T-linear term was clearly resolved as T-> 0, with a magnitude in good agreement with the value expected for a residual normal fluid with a nodal gap structure, together with a T^2-dependence at high temperatures. With an applied magnetic fields, the thermal conductivity grows rapidly, in dramatic contrast to fully gapped superconductors, and exhibits one-parameter scaling with T/sqrt{H}. These results place an important constraint on the order parameter symmetry, that is CePt_3Si is most likely to have line nodes.
We report on the Andreev spectroscopy and specific heat of high-quality single crystals BaFe$_{1.9}$Ni$_{0.1}$As$_{2}$. The intrinsic multiple Andreev reflection spectroscopy reveals two anisotropic superconducting gaps $Delta_L approx 3.2 textendash 4.5$,meV, $Delta_S approx 1.2 textendash 1.6$,meV (the ranges correspond to the minimum and maximum value of the coupling energy in the $k_xk_y$-plane). The $25 textendash 30 %$ anisotropy shows the absence of nodes in the superconducting gaps. Using a two-band model with s-wave-like gaps $Delta_L approx 3.2$,meV and $Delta_S approx 1.6$,meV, the temperature dependence of the electronic specific heat can be well described. A linear magnetic field dependence of the low-temperature specific heat offers a further support of s-wave type of the order parameter. We find that a d-wave or single-gap BCS theory under the weak-coupling approach cannot describe our experiments.
We report on measurements of the temperature dependence of the magnetic penetration depth of a very high quality single crystal of nonmagnetic superconductor LaPt3Si without inversion symmetry. The results are compared with those previously reported for the isostructural antiferromagnetic superconductor CePt3Si. At low temperatures, the penetration depth follows a BCS exponential behavior that implies an isotropic energy gap in LaPt3Si, in contrast to a linear response that indicates line nodes in CePt3Si. These line nodes have been argued to be protected by symmetry or accidentally generated by parity mixing. The present results provide support for the viewpoint that parity mixing alone does not seem to lead to unconventionality in CePt3Si and that it requires the antiferromagnetic order to be included.
We report a comprehensive study of the noncentrosymmetric superconductor Mo$_3$P. Its bulk superconductivity, with $T_c = 5.5$ K, was characterized via electrical resistivity, magnetization, and heat-capacity measurements, while its microscopic electronic properties were investigated by means of muon-spin rotation/relaxation ($mu$SR) and nuclear magnetic resonance (NMR) techniques. In the normal state, NMR relaxation data indicate an almost ideal metallic behavior, confirmed by band-structure calculations, which suggest a relatively high electron density of states, dominated by the Mo $4d$-orbitals. The low-temperature superfluid density, determined via transverse-field $mu$SR and electronic specific heat, suggest a fully-gapped superconducting state in Mo$_3$P, with $Delta_0= 0.83$ meV, the same as the BCS gap value in the weak-coupling case, and a zero-temperature magnetic penetration depth $lambda_0 = 126$ nm. The absence of spontaneous magnetic fields below the onset of superconductivity, as determined from zero-field $mu$SR measurements, indicates a preserved time-reversal symmetry in the superconducting state of Mo$_3$P and, hence, spin-singlet pairing.
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