Interplay between Ferromagnetism and Superconductivity in Tunneling Currents

Gronsleth, M. S.; Linder, Jacob; Børven, J.-M.; Sudbø, Asle

doi:10.1103/physrevlett.97.147002

Cited by 38 publications

(33 citation statements)

References 46 publications

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“…This has been noted by several authors in the context of superconductors coexisting with helimagnetic or spiral magnetic order 56,57 as well as ferromagnetic superconductors 54,55 . However, the spin-polarization of the Josephson current has not been studied in the arguably simplest case of a single ferromagnetic layer with inhomogeneous magnetization contacted by two conventional s-wave superconductors.…”

Section: Introductionmentioning

confidence: 54%

Spin-polarized Josephson current in superconductor/ferromagnet/superconductor junctions with inhomogeneous magnetization

et al. 2010

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We study numerically the properties of spin-and charge-transport in a current-biased nanoscale diffusive superconductor|ferromagnet|superconductor junction when the magnetization texture is non-uniform. Specifically, we incorporate the presence of a Bloch/Neel domain walls and conical ferromagnetism, including the role of spin-active interfaces. The superconducting leads are assumed to be of the conventional s-wave type. In particular, we investigate how the 0-π transition is influenced by the inhomogeneous magnetization texture and focus on the particular case where the charge-current vanishes while the spin-current is non-zero. In the case of a Bloch/Neel domain-wall, the spin-current can be seen only for one component of the spin polarization, whereas in the case of conical ferromagnetism the spin-current has the three components. This is in contrast to a scenario with a homogeneous exchange field, where the spin-current vanishes completely. We explain all of these results in terms of the interplay between the triplet anomalous Green's function induced in the ferromagnetic region and the local direction of the magnetization vector in the ferromagnet. Interestingly, we find that the spin-current exhibits discontinuous jumps at the 0-π transition points of the critical charge-current. This is seen both in the presence of a domain wall and for conical ferromagnetism. We explain this result in terms of the different symmetry obeyed by the current-phase relation when comparing the charge-and spin-current. Specifically, we find that whereas the charge-current obeys the well-known relation Ic(φ) = −Ic(2π − φ), the spin-current satisfies Is(φ) = Is(2π − φ), where φ is the superconducting phase difference.

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Section: Introductionmentioning

confidence: 54%

Spin-polarized Josephson current in superconductor/ferromagnet/superconductor junctions with inhomogeneous magnetization

et al. 2010

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“…14,15,16. In this paper, we follow up Ref. 17 with a more comprehensive study of the tunneling currents between two p-wave FMSC separated by an insulating junction; RuSr 2 GdCu 2 O 8 , UGe 2 , and URhGe have been proposed as candidates for such unconventional superconductors 4,5,6 . In our model, we assume uniform coexistence of the FM and SC order parameters and that superconductivity arises from the same electrons that are responsible for the magnetism.…”

Section: Introductionmentioning

confidence: 99%

Tunneling currents in ferromagnetic systems with multiple broken symmetries

2007

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A system exhibiting multiple simultaneously broken symmetries offers the opportunity to influence physical phenomena such as tunneling currents by means of external control parameters. In this paper, we consider the broken SU (2) (internal spin) symmetry of ferromagnetic systems coexisting with i) the broken U (1) symmetry of superconductors and ii) the broken spatial inversion symmetry induced by a Rashba term in a spin-orbit coupling Hamiltonian. In order to study the effect of these broken symmetries, we consider tunneling currents that arise in two different systems; tunneling junctions consisting of non-unitary spin-triplet ferromagnetic superconductors and junctions consisting of ferromagnets with spin-orbit coupling. In the former case, we consider different pairing symmetries in a model where ferromagnetism and superconductivity coexist uniformly. An interplay between the relative magnetization orientation on each side of the junction and the superconducting phase difference is found, similarly to that found in earlier studies on spin-singlet superconductivity coexisting with spiral magnetism. This interplay gives rise to persistent spin-and charge-currents in the absence of an electrostatic voltage that can be controlled by adjusting the relative magnetization orientation on each side of the junction. In the second system, we study transport of spin in a system consisting of two ferromagnets with spin-orbit coupling separated by an insulating tunneling junction. A persistent spin-current across the junction is found, which can be controlled in a well-defined manner by external magnetic and electric fields. The behavior of this spin-current for important geometries and limits is studied.

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“…Therefore nonequilibrium quantities are more desirable to compare with experimental data. Although some predictions are made on the properties of junctions with equal spin pairing(ESP) FS, 16,17,18,19 the study of tunneling spectra for possible candidate pairings of FS is insufficient.Tunneling spectroscopy provides an important information on the superconducting gap and its pairing symmetry. In normal metal / supercunductor junctions, Andreev reflection (AR) 20 is a key concept for low energy transport.…”

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confidence: 99%

Theory of the tunneling spectroscopy of ferromagnetic superconductors

2007

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We study tunneling conductance in normal metal / insulator / ferromagnetic superconductor junctions. The tunneling spectra show a clear difference between spin-singlet s-wave pairing, spintriplet opposite spin pairing and spin-triplet equal spin pairing: These pairings exhibit, respectively, gap struture, double peak structure and zero bias peak in the spectra. The obtained result may serve as a tool for determining the pairing symmetry of ferromagnetic superconductors.Magnetism and superconductivity have been under intensive pursuit in the field of low temperature physics. Recently the interplay of them has also attracted much attention because nontrivial phenomena are predicted or found experimentally. Such phenomena are expected to occur in ferromanget/superconductor junctions 1,2,3 and also in ferromangnetic superconductors (FS). Up to now, several bulk materials, e.g., UGe 2 4 , ZrZn 2 5 and URhGe 6 , are identified as FS. How Cooper pairs are formed in FS or under the coexistence of ferromagnetism and superconductivity is an interesting problem. However the pairing symmetries of FS are still controversial.Ferromagnetic superconductors seem to be triplet superconductors because singlet pairing and ferromagnetism are antagonist while triplet pairing have a uniform magnetic moment. However the possibility of swave pairing cannot be excluded. 7,8,9,10,11,12,13,14 For example it is predicted that UGe 2 can have s-wave superconductivity mediated by local ferromagnetic spins. 10,11The study of the nuclear relaxation rate cannot rule out the possibility of s-wave pairing in UGe 2 .12,13 A weak ferromagnetic Fermi liquid theory also suggests the possibility of s-wave superconductivity.14 Therefore detailed comparison between theoretical predictions and experimantal data is required to settle this problem. Then the properties of thermodynamic quantities should be noted: For example equilibrium thermodynamic quantities for Balian-Werthamer state of p-wave pairing, which is realized in B phase of 3 He, are expected to show swave property because its gap is constant.15 In this way, equilibrium thermodynamic quantities for p-wave pairing could not be clearly distinguished from those of s-wave pairing. Therefore nonequilibrium quantities are more desirable to compare with experimental data. Although some predictions are made on the properties of junctions with equal spin pairing(ESP) FS, 16,17,18,19 the study of tunneling spectra for possible candidate pairings of FS is insufficient.Tunneling spectroscopy provides an important information on the superconducting gap and its pairing symmetry. In normal metal / supercunductor junctions, Andreev reflection (AR) 20 is a key concept for low energy transport. Blonder, Tinkham and Klapwijk (BTK) formulated the tunneling conductance where the AR is taken into account 21 . This enables us to study the energy gap of superconductors. The generalization of the BTK formula for normal metal / unconventional superconductor junctions are also useful to study the properties of unconvent...

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Interplay between Ferromagnetism and Superconductivity in Tunneling Currents

Cited by 38 publications

References 46 publications

Spin-polarized Josephson current in superconductor/ferromagnet/superconductor junctions with inhomogeneous magnetization

Spin-polarized Josephson current in superconductor/ferromagnet/superconductor junctions with inhomogeneous magnetization

Tunneling currents in ferromagnetic systems with multiple broken symmetries

Theory of the tunneling spectroscopy of ferromagnetic superconductors

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