High-pressure synthesis techniques have allowed for the growth of Sn1-xInxTe samples beyond the ambient In-saturation limit of x = 0.5 (T-c similar to 4.5 K). In this study we present measurements of the temperature dependence of the London penetration depth Delta lambda(T) in this superconducting doped topological insulator for x = 0.7, where T-c(,onset) approximate to 5 K. The results indicate fully gapped BCS-like behavior, ruling out odd-parity A(2u), pairing; however, odd-parity A(1u) in pairing is still possible. Critical field values measured below 1 K and other superconducting parameters are also presented.

High-pressure synthesis techniques have allowed for the growth of Sn_1-xIn_xTe samples beyond the ambient In-saturation limit of x = 0.5 (T_c ∼ 4.5 K). In this study, we present measurements of the temperature dependence of the London penetration depth Δλ(T) in this superconducting doped topological insulator for x = 0.7, where T_c,onset≈ 5 K. The results indicate fully gapped BCS-like behavior, ruling out odd-parity A_2u pairing; however, odd-parity A_1u pairing is still possible. Critical field values measured below 1 K and other superconducting parameters are also presented.

A new critical-current-by-design paradigm is presented. It aims at predicting the optimal defect landscape in superconductors for targeted applications by elucidating the vortex dynamics responsible for the bulk critical current. To this end, critical current measurements on commercial high-temperature superconductors are combined with large-scale time-dependent Ginzburg-Landau simulations of vortex dynamics.

Iron-based superconductors could be useful for electricity distribution and superconducting magnet applications because of their relatively high critical current densities and upper critical fields. SmFeAsO0.8F0.15 is of particular interest as it has the highest transition temperature among these materials. Here we show that by introducing a low density of correlated nano-scale defects into this material by heavy-ion irradiation, we can increase its critical current density to up to 2 × 107 A cm−2 at 5 K—the highest ever reported for an iron-based superconductor—without reducing its critical temperature of 50 K. We also observe a notable reduction in the thermodynamic superconducting anisotropy, from 8 to 4 upon irradiation. We develop a model based on anisotropic electron scattering that predicts that the superconducting anisotropy can be tailored via correlated defects in semimetallic, fully gapped type II superconductors. Iron-based superconductors could be useful in the development of superconducting magnets and related applications. Fang et al. show that a low density of columnar defects in SmFeAsO0.8F0.15can increase its critical current to record-high values and reduce its superconducting anisotropy.

We present specific heat measurements on a series of BaFe2(As1-xPx)2 single crystals with phosphorous doping ranging from x = 0.3 to 0.55. Our results reveal that BaFe2(As1-xPx)2 follows the scaling Delta_C/Tc ~ Tc^2 remarkably well. The clean-limit nature of this material imposes new restraints on theories aimed at explaining the scaling. Furthermore, we find that the Ginzburg-Landau parameter decreases significantly with doping whereas the superconducting anisotropy is gamma~2.6, independent of doping.

Each discovery of a new high temperature superconductor drives the expectation that advanced engineering of materials defect structures will enable effective vortex pinning and high values of the electrical current density. Here, we demonstrate that single crystals of the iron-based superconductor Ba0.6K0.4Fe2As2 with T-c = 37.5K can accommodate an unprecedented large concentration of strong-pinning defects in the form of discontinuous nm-sized nanorods with no degradation of the superconducting transition temperature. At a temperature of 5K, we find a critical current density of 5 MA/cm(2) that is magnetic field independent in fields up to 7 T. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731204]

We report on the specific-heat determination of the anisotropic phase diagram of single crystals of optimally doped SmFeAsO1-xFx. In zero field, we find a clear cusplike anomaly in C/T with Delta C/T-c = 24 mJ/mol K-2 at T-c = 49.5 K. In magnetic fields along the c axis, pronounced superconducting fluctuations induce broadening and suppression of the specific-heat anomaly which can be described using three-dimensional lowest-Landau-level scaling with an upper critical field slope of -3.5 T/K and an anisotropy of Gamma = 8. The small value of Delta C/T-c yields a Sommerfeld coefficient gamma similar to 8 mJ/mol K-2, indicating that SmFeAsO1-xFx is characterized by a modest density of states and strong coupling.

— A steady-state ac-temperature micro-calorimeter for heat capacity measurement of sub-microgram superconducting samples is presented. It utilizes thermocouple thermometers nano-patterned onto 150 nm thick Si 3 N 4 membranes. Theoretical models, mathematical relations describing the operation of the calorimeter and cal-ibration procedures are discussed. The system achieves a resolution of 10 − 4 ; and allows for measurements from 5 K to room temperature. The calorimeter can be continuously rotated in a split-coil magnet generating up to 8 T. To demonstrate the performance of our device we present measurements of the specific heat of single crystals of SmFeAsO 0 . 85 F 0 . 15 (120 µ m wide and 10 µ m thick, crystal w1) and of BaFe 2 (As 1 − x P x ) 2 (150 µ m wide and 30 µ m thick).

Here we report normal-state conductance measurements of three different types of superconducting tunnel junctions that are being used or proposed for quantum computing applications: p-Al/a-AlO/p-Al, e-Re/e-AlO/p-Al, and e-V/e-MgO/p-V, where p stands for polycrystalline, e for epitaxial, and a for amorphous. All three junctions exhibited significant deviations from the parabolic behavior predicted by the WKB approximation models. In the p-Al/a-AlO/p-Al junction, we observed enhancement of tunneling conductances at voltages matching harmonics of Al-O stretching modes. On the other hand, such Al-O vibration modes were missing in the epitaxial e-Re/e-AlO/p-Al junction. This suggests that absence or existence of the Al-O stretching mode might be related to the crystallinity of the AlO tunnel barrier and the interface between the electrode and the barrier. In the e-V/e-MgO/p-V junction, which is one of the candidate systems for future superconducting qubits, we observed suppression of the density of states at zero bias. This implies that the interface is electronically disordered, presumably due to oxidation of the vanadium surface underneath the MgO barrier, even if the interface was structurally well ordered, suggesting that the e-V/e-MgO/p-V junction will not be suitable for qubit applications in its present form. This also demonstrates that the normal-state conductance measurement can be effectively used to screen out low quality samples in the search for better superconducting tunnel junctions.