Point contact Andreev reflection spectra have been taken as a function of temperature and magnetic field on the polycrystalline form of the newly discovered iron-based superconductor Sr 2 ScFePO 3 . A zero bias conductance peak which disappears at the superconducting transition temperature, dominates all of the spectra. Data taken in high magnetic fields show that this feature survives until 7T at 2K and a flattening of the feature is observed in some contacts. Here we inspect whether these observations can be interpreted within a d-wave, or nodal order parameter framework which would be consistent with the recent theoretical model where the height of the P in the Fe-P-Fe plane is key to the symmetry of the superconductivity. However, in polycrystalline samples care must be taken when examining Andreev spectra to eliminate or take into account artefacts associated with the possible effects of Josephson junctions and random alignment of grains.

We wish to correct two errors in the paper. The removal of these errors does not affect the results and conclusions of this paper.(1) Page 3, 2nd paragraph in Results section should read as follows: "In order to fit the data, the spectra for the single crystal were normalized to the conductance spectra obtained either using a nonsuperconducting Pt tip, as shown in Fig. 2(b), or from a Nb tip, where the spectra were taken at temperatures above and close to the superconducting critical temperature (11.7 K).(2) To withdraw one set of data [triangles shown in Figs. 3(a), 4(a), and 4(b)], because the P and Z trends as a function of contact resistance were found to be dependent on normalization procedure and therefore are not robust.

In a number of recent experiments, holmium has been shown to promote spin triplet pairing when in proximity to a spin singlet superconductor. The condition for the support of spin triplet pairing is that the ferromagnet should have an inhomogeneous magnetic state at the interface with the superconductor. Here we use Andreev reflection spectroscopy to study the properties of single ferromagnet/superconductor interfaces formed of holmium and niobium, as a function of the contact resistance of the junction between them. We find that both single crystal and c-axis oriented thin film holmium show unusual behavior for low junction contact resistance, characteristic of spin mixing type properties, which are thought necessary to underpin spin triplet formation. We also explore whether this signature is observed when the junction is formed of Ni 19 Pd 81 and niobium.

No abstract