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Register a new userMagnetic response of noncentrosymmetric superconductor La2C3: Effect of double-gap and spin-orbit interaction
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The presence of spin-orbit (SO) interaction in a noncentrosymmetric superconductor, La2C3 (T_c~11 K) is demonstrated by muon spin rotation (muSR) in its normal state, where muSR spectra exhibit field-induced weak depolarization due to van Vleck-like local susceptibility. In the mixed state, muon spin relaxation due to inhomogeneity of internal field (sigma_v) exhibits a field dependence that is characterized by a kink, where sigma_v (and hence the superfluid density) is more strongly reduced at lower fields. This is perfectly in line with the presence of a secondary energy gap previously inferred from the temperature dependence of sigma_v, and also consistent with the possible influence of asymmetric deformation of the Fermi surface due to the SO interaction.
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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.
We report measurements of the temperature dependence of the magnetic penetration depth in different quality polycrystalline samples of noncentrosymmetric LaNiC2 down to 0.05 K. This compound has no magnetic phases and breaks time-reversal symmetry. In our highest quality sample we observe a T^2 dependence below 0.4Tc indicative of nodes in the energy gap. We argue that previous results suggesting conventional s-wave behavior may have been affected by magnetic impurities.
We calculate the Josephson current between two one-dimensional (1D) nanowires oriented along $x$ with proximity induced $s$-wave superconducting pairing and separated by a narrow dielectric barrier in the presence of both Rashba spin-orbit interaction (SOI) characterized by strength $alpha$ and Zeeman fields ($h$ along $hat z$ and ${bf B}$ in the $x-y$ plane). We formulate a general method for computing the Andreev bound states energy which allows us to obtain analytical expressions for the energy of these states in several asymptotic cases. We find that in the absence of the magnetic fields the energy gap between the Andreev bound states decreases with increasing Rashba SOI constant leading eventually to touching of the levels. In the absence of Rashba SOI, the Andreev bound states depend on the magnetic fields and display oscillatory behavior with orientational angle of B leading to magneto-Josephson effect. We also present analytic expressions for the dc Josephson current charting out their dependence on ${bf B}$, $h$, and $alpha$. We demonstrate the existence of finite spin-Josephson current in these junctions in the presence of external magnetic fields and provide analytic expressions for its dependence on $alpha$, $bf B$ and $h$. Finally, we study the AC Josephson effect in the presence of the SOI (for $|{bf B}|=h=0$) and an external radiation and show that the width of the resulting Shapiro steps in such a system can be tuned by varying $alpha$. We discuss experiments which can test our theoretical results.
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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