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Register a new userStudies of the superconducting properties of Sn1-xInxTe (x=0.38 to 0.45) using muon-spin spectroscopy
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The superconducting properties of Sn1-xInxTe (x = 0.38 to 0.45) have been studied using magnetization and muon-spin rotation or relaxation (muSR) measurements. These measurements show that the superconducting critical temperature Tc of Sn1-xInxTe increases with increasing x, reaching a maximum at around 4.8 K for x = 0.45. Zero-field muSR results indicate that time-reversal symmetry is preserved in this material. Transverse-field muon-spin rotation has been used to study the temperature dependence of the magnetic penetration depth lambda(T) in the mixed state. For all the compositions studied, lambda(T) can be well described using a single-gap s-wave BCS model. The magnetic penetration depth at zero temperature lambda(0) ranges from 500 to 580 nm. Both the superconducting gap Delta(0) at 0 K and the gap ratio Delta(0)/kBTc indicate that Sn1-xInxTe (x = 0.38 to 0.45) should be considered as a superconductor with intermediate to strong coupling.
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We have performed angle-resolved photoemission spectroscopy of the strongly spin-orbit coupled low-carrier density superconductor Sn1-xInxTe (x = 0.045) to elucidate the electronic states relevant to the possible occurrence of topological superconductivity recently reported for this compound from point-contact spectroscopy. The obtained energy-band structure reveals a small holelike Fermi surface centered at the L point of the bulk Brillouin zone, together with a signature of a topological surface state which indicates that this superconductor is essentially a doped topological crystalline insulator characterized by band inversion and mirror symmetry. A comparison of the electronic states with a band-non-inverted superconductor possessing a similar Fermi surface structure, Pb1-xTlxTe, suggests that the anomalous behavior in the superconducting state of Sn1-xInxTe is likely to be related to the peculiar orbital characteristics of the bulk valence band and/or the presence of a topological surface state.
In a recent article Tran et al. [Phys. Rev.B 78, 172505 (2008)] report on the result of the muon-spin rotation (muSR) measurements of Mo_3Sb_7 superconductor. Based on the analysis of the temperature and the magnetic field dependence of the Gaussian relaxation rate sigma_{sc} they suggest that Mo_3Sb_7 is the superconductor with two isotropic s-wave like gaps. An additional confirmation was obtained from the specific heat data published earlier by partly the same group of authors in [Acta Mater. 56, 5694 (2008)]. The purpose of this Comment is to point out that from the analysis made by Tran et al. the presence of two superconducting energy gaps in Mo_3Sb_7 can not be justified. The analysis of muSR data does not account for the reduction of sigma_{sc} with increasing temperature, and, hence, yields inaccurate information on the magnetic penetration depth. The specific heat data can be satisfactory described within the framework of the one-gap model with the small residual specific heat component. The experimental data of Tran et al., as well as our earlier published muSR data [Phys. Rev. B 78, 014502 (2008)] all seem to be consistent with is the presence of single isotropic superconducting energy gap in Mo_3Sb_7.
Preliminary evidence for the occurrence of high-Tc superconductivity in alkali-doped organic materials, such as potassium-doped p-terphenyl (KPT), were recently obtained by magnetic susceptibility measurements and by the opening of a large superconducting gap as measured by ARPES and STM techniques. In this work, KPT samples have been synthesized by a chemical method and characterized by low-temperature Raman scattering and resistivity measurements. Here, we report the occurrence of a resistivity drop of more than 4 orders of magnitude at low temperatures in KPT samples in the form of compressed powder. This fact was interpreted as a possible sign of a broad superconducting transition taking place below 90 K in granular KPT. The granular nature of the KPT system appears to be also related to the 20 K broadening of the resistivity drop around the critical temperature.
In this work we investigate superconducting properties of niobium samples via application of the muon spin rotation/relaxation (muSR) technique. We employ for the first time the muSR technique to study samples that are cutout from large and small grain 1.5 GHz radio frequency (RF) single cell niobium cavities. The RF test of these cavities was accompanied by full temperature mapping to characterize the RF losses in each of the samples. Results of the muSR measurements show that standard cavity surface treatments like mild baking and buffered chemical polishing (BCP) performed on the studied samples affect their surface pinning strength. We find an interesting correlation between high field RF losses and field dependence of the sample magnetic volume fraction measured via muSR. The muSR line width observed in ZF-muSR measurements matches the behavior of Nb samples doped with minute amounts of Ta or N impurities. An upper bound for the upper critical field Hc2 of these cutouts is found.
The thermal conductivity of electron-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals is investigated below 200K, with an emphasis on the behavior near the magnetic and superconducting (T_c) transition temperatures. An enhancement of the in-plane thermal conductivity $kappa_{ab}$ is observed below T_c for all samples, with the greatest enhancement observed near optimal doping. The observed trends are consistent with the scattering of heat carriers by low-energy magnetic excitations. Upon entering the superconducting state, the formation of a spin-gap leads to reduced scattering and an enhancement in $kappa(T)$. Similarly, an enhancement of $kappa$ is observed for polycrystalline BaFe2As2 below the magnetic transition, and qualitative differences in $kappa(T)$ between single crystalline and polycrystalline BaFe2As2 are utilized to discuss anisotropic scattering. This study highlights how measuring $kappa$ near $T_c$ in novel superconductors can be useful as a means to probe the potential role of spin fluctuations.
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