Multigap superconductivity in ThAsFeN investigated using muSR measurements

Abstract

We have investigated the superconducting ground state of the newly discovered superconductor ThFeAsN with a tetragonal layered crystal structure using resistivity, magnetization, heat capacity and transverse-field (TF) muon-spin rotation ($\mu$SR) measurements. Our resistivity and magnetization measurements reveal an onset of bulk superconductivity with $T_{\mathbf{c}}\sim$ 30 K. The heat capacity results show a very small anomaly, $\Delta$C${}_{ele}$$\sim$0.214 (J/mol-K) at $T_{\mathbf{c}}\sim$ 30 K and exhibits exponential behavior below $T_{\mathbf{c}}$, which fits better to two superconducting gaps rather than a single gap. Further a nonlinear magnetic field dependence of the electronic specific heat coefficient $\gamma$(H) has been found in the low temperature limit, which indicates that the smaller energy gap is nodal. Our analysis of the TF-$\mu$SR results shows that the temperature dependence of the superfluid density is better described by a two-gap model either isotropic $s$+$s$-wave or $s$+$d$-wave than a single gap isotropic $s$-wave model for the superconducting gap, consistent with other Fe-based superconductors. The combine $\gamma$(H) and TF-$\mu$SR results confirm $s$+$d$-wave model for the gap structure of ThFeAsN. The observation of two gaps in ThFeAsN suggests multiband nature of the superconductivity possibly arising from the d-bands of Fe ions. Furthermore, from our TF-$\mu$SR study we have estimated the magnetic penetration depth, in the polycrystalline sample, of ${\lambda }_{\mathrm{L}}$$(0)$ = 375 nm, superconducting carrier density $n_s=4.6\times 10^{27}$m${}^{-3}$, and carrier's effective-mass $m^{\ast }$ = 2.205\textit{m}${}_e$. We will compare the results of our present study with those reported for the Fe-pnictide family of superconductors.

8 pages, 5 figures. arXiv admin note: text overlap with arXiv:1602.06976

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• Unconventional superconductivity in the cage type compound Sc${}_5$Rh${}_6$Sn${}_{18}$
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