Controllable 0 − π transition in iron pnictide superconductor junctions with a spacer of strong ferromagnet

Abstract

We investigate the control of 0−π transition in Josephson junctions consisting of a highly spin-polarized ferromagnet coupled to two iron pnictide superconductors (SCs). It is shown that, a 0−π transition as a function of interband coupling strength is always exhibited, which can be experimentally used to discriminate the s±-wave pairing symmetry in the iron pnictide SCs from the s++-wave one in MgB2. By tuning the doping level in the s±-wave SCs, one can vary the interband coupling strength so as to obtain the controllable 0−π transition. This device may be realized with current technologies and has practical use in Cooper pair spintronics and quantum information.

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

“…The statistical data obtained so far on the flux quantization in polycrystalline NdFeAsO 0.88 F 0.12 [65] provide indirect evidence for the existence of Josephson loops with a π phase shift in support of the sign-changing s ± gap symmetry. More "pure" experiments on individual Josephson junctions with controlled orientation and on a broader range of compounds are in principle possible [100,105], but still await practical realization. While there appears to be no single smoking-gun experiment so far that could unequivocally demonstrate the sign change of the order parameter in iron-based super-conductors or single out the pairing boson, proponents of spin-fluctuation theories find multiple supporting evidence in spectral signatures of collective magnetic excitations in the electronic structure or, vice versa, of the superconducting gap opening in the spin-fluctuation spectra.…”

Interplay between interband coupling and ferromagnetism in iron pnictide superconductor/ferromagnet/iron pnictide superconductor junctions

“…Accordingly, the net Josephson current the spin-up channels carry is in the direction opposite to that for spindown channels, which is also just the case of s-wave SC/FM/ s-wave SC junctions. 14 Similarly, in Figs. 5(a) and 5(b), the twofold ARs a 1 1ð2Þr and a 1 0 1ð2Þr in s þþ -wave SC/FM/s þþ -wave SC structures are also, respectively, shown as a function of a for the incident ELQs and HLQs.…”

“…It has two s-wave energy gaps with the same phase in r and p bands, known as s þþ pairing symmetry. 14 While for the iron-based SCs, owing to the vastness of the iron-based SC family, discrepancies from different measurements and controversies remain unsolved. 3,4 A wide variety of possible pairing states, such as p-wave, 5 d-wave, 6 extended s-wave, or s 6 -wave, have been predicted.…”

Shot noise as a probe for the pairing symmetry of iron pnictide superconductors

“…Further, doping Ip superconductors can tune the inter-band coupling strength (α) as mentioned in ref. [24]. Experimentally, doping cobalt atoms in the Ip superconductor Ba(Fe 1−x Co x ) 2 As 2 can tune the interband coupling to strong coupling at optimal doping, see ref.…”