Evidence for nodal superconductivity in Sr₂ScFePO₃

Abstract

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.

Spin fluctuations in iron pnictides and chalcogenides: From antiferromagnetism to superconductivity

“…Moreover, the much broader variety of crystal structures and chemical compositions among different families of ferropnictides makes it generally unlikely that conclusions drawn for a single material can be straightforwardly generalized for the whole class of compounds. For instance, while the nodeless s ± symmetry of the superconducting order parameter has been suggested for some of the most actively studied families with the highest values of T c [63][64][65][66], a few other iron-arsenide compounds display nodes in the gap structure, most notably LaFePO [67][68][69][70], LiFeP [71], Sr 2 ScFePO 3 [72], BaFe 2 (As 1−x P x ) 2 [73][74][75], KFe 2 As 2 [76][77][78][79] and RbFe 2 As 2 [80], evidencing a qualitatively different type of order-parameter symmetry, possibly a nodal s ± [81] or d-wave [82]. Since KFe 2 As 2 represents the end member of the Ba 1−x K x Fe 2 As 2 series of superconductors, the presence of nodes in its gap structure implies that the superconducting gap undergoes a qualitative change of symmetry as a function of a continuously tunable parameter, such as doping [83] or hydrostatic pressure [79].…”

Emergent phases of nodeless and nodal superconductivity separated by antiferromagnetic order in iron-based superconductor (Ca4Al2O6Kinouchi1, Mukuda2, Kitaoka3 et al. 2013Phys. Rev. B223221View full textAdd to dashboardCite

“…On the other hand, when h P n < 1.32Å, the nodal SC takes place for Ae122(As,P) (Ae = Ba,Sr), [16][17][18][19]22 LiFeP, 15 LaFePO, 31,32 and (Sr 4 Sc 2 O 6 )Fe 2 P 2 . 33 In this context, the quite unique and important ingredient found in Al-42622(As,P) is that the nodeless SC and the nodal SC are separated by the onset of AFM order. According to this empirical rule, it is reasonably understood that in the parent (111) compounds without any chemical doping, LiFeAs, and LiFeP 14,15 exhibit the nodeless and nodal SC, respectively, whereas NaFeAs exhibits the AFM order.…”

Absence of strong magnetic fluctuations in FeP-based systems LaFePO and Sr2ScO3FeP

“…They generally have lower T c values, and the stoichiometric compounds do not undergo magnetic or structural phase transitions [8][9][10][11][12]. Evidence has been found for a nodal superconducting order parameter in LaFePO [13][14][15], Sr 2 ScO 3 FeP [16] and LiFeP [17], in contrast to many of the iron arsenide and selenide superconductors. The difference in gap structure has been explained by the absence of a Fermi surface hole pocket centred on the M point in the Brillouin zone in the phosphides [18].…”