Tunneling currents in ferromagnetic systems with multiple broken symmetries

Linder, Jacob; Gronsleth, M. S.; Sudbø, Asle

doi:10.1103/physrevb.75.024508

Cited by 64 publications

(70 citation statements)

References 62 publications

(92 reference statements)

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“…25 the transport properties of a S/F junction were calculated by using the Blonder-Tinkham-Klapwijk formalism. 26 This analysis was extended in several other works [27][28][29][30][31][32][33] for S/F and S/F /S junctions in the ballistic and diffusive limit by taking into account spin-active interfaces between the F and S layers. 34,35 In particular, the results for the diffusive limit presented in those works have been obtained by using the boundary conditions for the quasiclassical Green's functions derived in Ref.…”

Section: Introductionmentioning

confidence: 99%

Electronic transport through ferromagnetic and superconducting junctions with spin-filter tunneling barriers

2012

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We present a theoretical study of the quasiparticle and subgap conductance of generic X/I sf /S M junctions with a spin-filter barrier I sf , where X is either a normal N or a ferromagnetic metal F and S M is a superconductor with a built-in exchange field. Our study is based on the tunneling Hamiltonian and the Green's-function technique. First, we focus on the quasiparticle transport, both above and below the superconducting critical temperature. We obtain a general expression for the tunneling conductance which is valid for arbitrary values of the exchange field and arbitrary magnetization directions in the electrodes and in the spin-filter barrier. In the second part, we consider the subgap conductance of a N/I sf /S junction, where S is a conventional superconductor. In order to account for the spin-filter effect at interfaces, we heuristically derive boundary conditions for the quasiclassical Green's functions. With the help of these boundary conditions, we show that the proximity effect and the subgap conductance are suppressed by spin filtering in a N/I sf /S junction. Our work provides useful tools for the study of spin-polarized transport in hybrid structures both in the normal and in the superconducting state.

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Section: Introductionmentioning

confidence: 99%

Electronic transport through ferromagnetic and superconducting junctions with spin-filter tunneling barriers

2012

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“…a Blonder-Tinkham-Klapwijk (BTK) 72 framework. Explicitly spin-active barriers were considered in ballistic S|F bilayers using the BTK-approach for both s-wave 73 and d-wave 74 superconductors. In the absence of spin-DIPS (G φ,j → 0), Eq.…”

Section: Discussionmentioning

confidence: 99%

Theory of superconducting and magnetic proximity effect in S/F structures with inhomogeneous magnetization textures and spin-active interfaces

2009

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We present a study of the proximity effect and the inverse proximity effect in a superconductor|ferromagnet bilayer, taking into account several important factors which mostly have been ignored in the literature so far. These include spin-dependent interfacial phase shifts (spin-DIPS) and inhomogeneous textures of the magnetization in the ferromagnetic layer, both of which are expected to be present in real experimental samples. Our approach is numerical, allowing us to access the full proximity effect regime. In Part I of this work, we study the superconducting proximity effect and the resulting local density of states in an inhomogeneous ferromagnet with a non-trivial magnetic texture. Our two main results in Part I are a study of how Bloch and Néel domain walls affect the proximity-induced superconducting correlations and a study of the superconducting proximity effect in a conical ferromagnet. The latter topic should be relevant for the ferromagnet Ho, which was recently used in an experiment to demonstrate the possibility to generate and sustain long-range triplet superconducting correlations. In Part II of this work, we investigate the inverse proximity effect with emphasis on the induced magnetization in the superconducting region as a result of the "leakage" from the ferromagnetic region. It is shown that the presence of spin-DIPS modify conclusions obtained previously in the literature with regard to the induced magnetization in the superconducting region. In particular, we find that the spin-DIPS can trigger an anti-screening effect of the magnetization, leading to an induced magnetization in the superconducting region with the same sign as in the proximity ferromagnet.

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Section: Pacs Numbersmentioning

confidence: 99%

“…However, the nonsuperconducting material does not necessarily have to be a simple normal metal. Instead, it may feature intrinsic properties, such as magnetism, which then provide an arena for studying the interplay between superconductivity and different types of electronic ordering [12].A natural question arises: could such an interplay be useful in order to extract information about the superconducting state? In this Letter, we demonstrate that a ferromagnet|triplet superconductor bilayer provides an appealingly simple and powerful method of clearly distinguishing between different types of triplet pairing states, thus providing information about the nature of the superconducting condensate.…”

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confidence: 99%

Spin-sensitive long-range proximity effect in ferromagnet/spin-triplet-superconductor bilayers

et al. 2011

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The discovery of noncentrosymmetric superconductors, such as CePt 3 Si, and chiral superconductors, such as Sr 2 RuO 4 , calls for experimental methods to identify the presence of spin-triplet pairing. We here demonstrate a method which accomplishes this in an appealingly simple manner: a spin-sensitive proximity effect in a ferromagnet|triplet superconductor bilayer. It is shown how the orientation of the field can be used to unambiguously distinguish between different spin-triplet states. Moreover, the proximity effect becomes long-ranged in spite of the presence of an exchange field and even without any magnetic inhomogeneities, in contrast to conventional S|F junctions. Our results can be verified by STM-spectroscopy and could be useful as a tool to characterize the pairing state in unconventional superconducting materials. PACS numbers:Superconductivity may be defined as conventional or unconventional depending on the properties of the pairing state and whether or not multiple broken symmetries are present in the system. In conventional superconductors, the pairing state belongs to the trivial representation of the point-group and the system ground state breaks the U(1) gauge symmetry. On the other hand, unconventional superconductors display pairing symmetries belonging to higher-dimensional representations of the point group and may also exhibit multiple broken symmetries in the ground state. Examples of the latter are ferromagnetic superconductors [1] with simultaneously broken U(1) and SU(2) symmetries due to the presence of an intrinsic magnetization, and noncentrosymmetric superconductors [2], where the absence of a definite parity of the lattice leads to the mixing of even-and odd-parity superconducting order parameters.In order to characterize the properties of a superconducting system, much relies on determining the orbital-and spinsymmetry of the order parameter (OP), a topic currently under intense investigation [3][4][5][6][7]. To acquire information about the order parameter, it is often useful to study how the superconducting correlations behave when placed in proximity to a non-superconducting material such as a normal metal. This idea has been employed previously in several works studying e.g. normal metal|non-centrosymmetric superconductor (N|NCS) junctions [8][9][10][11] in order to look for unique signatures of the superconducting OP. However, the nonsuperconducting material does not necessarily have to be a simple normal metal. Instead, it may feature intrinsic properties, such as magnetism, which then provide an arena for studying the interplay between superconductivity and different types of electronic ordering [12].A natural question arises: could such an interplay be useful in order to extract information about the superconducting state? In this Letter, we demonstrate that a ferromagnet|triplet superconductor bilayer provides an appealingly simple and powerful method of clearly distinguishing between different types of triplet pairing states, thus providing information about the natu...

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Tunneling currents in ferromagnetic systems with multiple broken symmetries

Cited by 64 publications

References 62 publications

Electronic transport through ferromagnetic and superconducting junctions with spin-filter tunneling barriers

Electronic transport through ferromagnetic and superconducting junctions with spin-filter tunneling barriers

Theory of superconducting and magnetic proximity effect in S/F structures with inhomogeneous magnetization textures and spin-active interfaces

Spin-sensitive long-range proximity effect in ferromagnet/spin-triplet-superconductor bilayers

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