Surface effects in magnetic superconductors with a spiral magnetic structure

Volkov, A. N.

doi:10.1103/physrevb.77.064521

Cited by 5 publications

(4 citation statements)

References 33 publications

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“…Only near the surface of the sample, the triplet component with a nonzero projection of S on h(r) appears; it decays exponentially away from the surface [41].…”

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confidence: 99%

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Nematic versus ferromagnetic spin filtering of triplet Cooper pairs in superconducting spintronics

2015

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We consider two types of magnetic Josephson junctions (JJ). They are formed by two singlet superconductors S and magnetic layers between them so that the JJ is a heterostructure of the S m /n/S m type, where S m includes two magnetic layers with non-collinear magnetization vectors. One layer is represented by a weak ferromagnet and another one-the spin filter-is either conducting strong ferromagnet (nematic or N-type JJ) or magnetic tunnel barrier with spin-dependent transparency (magnetic or M-type JJ). Due to spin filtering only fully polarized triplet component penetrates the normal n wire and provides the Josephson coupling between the superconductors S. Although both filters let to pass triplet Cooper pairs with total spin S parallel to the filter axes, the behavior of nematic and magnetic JJs is completely different. Whereas in the nematic case the charge and spin currents, I Q and I sp , do not depend on mutual orientation of the filter axes, both currents vanish in magnetic JJ in case of antiparallel filter axes, and change sign under reversing the filter direction. The obtained expressions for I Q and I sp show clearly a duality between the superconducting phase ϕ and the angle α between the exchange fields in the weak magnetic layers. PACS numbers: 74.78.Fk, 85.25.Cp, 74.45.+c Triplet Cooper pairing is known to exist in superfluid 3 He [1, 2]. As concerns superconductors, the situation is less clear. Although some indication for the triplet superconductors has been found in a number of completely different classes of materials [3][4][5], a general consensus about the existence of the triplet superconductivity in the organic metals, heavy fermions and other interesting materials investigated from this point of view has not been achieved [6,7]. In principle, the fact that the spins of the fermions of the Cooper pairs are equal to each other does not contradict the Pauli principle because the condensate wave function f (p) and the order parameter ∆ tr (p) in these triplet superconductors are odd functions of the momentum p. In contrast to the conventional BCS superconductivity, the triplet superconductivity with such a symmetry of the order parameter is sensitive to impurity scattering [8] and, therefore, it is usually strongly suppressed by disorder.However, the triplet Cooper pairs can appear already in conventional singlet superconductors provided an external magnetic (H) or an internal exchange (h) field acts on the spins of electrons. [8][9][10][11] A triplet component inevitably arises also in magnetic superconductors [12].The triplet condensate function arising from the singlet superconductivity in the presence of the magnetic or exchange field acting on spins is odd in frequency and therefore may still have an s-wave space symmetry without violating the Pauli principle. It has a component with the 0-spin projection f tr,0 ∝ 〈ĉ ↑ĉ↓ (t ) +ĉ ↓ĉ↑ (t )〉 on the direction of the field h or H but also the components with spin projection ±1. The zero projection component f tr,0 of the condensate functio...

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“…Only near the surface of the sample, the triplet component with a nonzero projection of S on h(r) appears; it decays exponentially away from the surface [41].…”

mentioning

confidence: 99%

“…Note that the triplet component that arises in magnetic superconductors with a spiral h(r) [12,40] has zero projection of the total spin of triplet Cooper pairs S on h(r). Only near the surface of the sample, the triplet component with a nonzero projection of S on h(r) appears; it decays exponentially away from the surface [41].…”

mentioning

confidence: 99%

Nematic versus ferromagnetic spin filtering of triplet Cooper pairs in superconducting spintronics

2015

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“…A second possibility is a magnetically disordered or "spin-active" interface [12,13]. Finally, the triplet proximity effect can be caused by variations of the magnetization direction m associated with a domain wall, either perpendicular [14] or parallel to the superconductor interface [15]. Although domain walls occur generically in half metals and ferromagnets, at first sight they are an unlikely source of the triplet proximity effect, because (1) only domain walls that happen to be immediately at the superconductor interface can contribute to the triplet proximity effect and (2) the spin-flip scattering amplitude in a domain wall is small as 1/(k F l d ), where k F is the Fermi wavelength and l d the width of the domain wall [5].…”

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confidence: 99%

Enhanced triplet Andreev reflection off a domain wall in a lateral geometry

Kupferschmidt

Brouwer

2009

Phys. Rev. B

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We find that the triplet Andreev reflection amplitude at the interface between a half-metal and an s-wave superconductor in the presence of a domain wall is significantly enhanced if the half-metal is coupled laterally to the superconductor. Whereas triplet Andreev reflection is absent at the Fermi energy in the case of serial coupling, it is nonzero in a lateral contact geometry. We also find that in the lateral case domain walls cause ͑Andreev͒ backscattering even in the adiabatic limit of long domain walls, contrary to adiabatic domain walls in ordinary magnetic systems. For a lateral contact, domain walls can thus be an effective source of the triplet proximity effect.

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“…(2) and (3) after substituting the values of the GFs at the interface. 52 For simplicity we assume that the thickness of the S and F layers (t S ,t F ) is smaller than the characteristic length over which the GFs vary. In such a case one can average the quasiclassical equations over the thickness of the F-S bilayer that is now described by an effective exchange field (h) and superconducting order parameter ( ) defined by 51 …”

Section: Modelmentioning

confidence: 99%

Phase-dependent heat transport through magnetic Josephson tunnel junctions

Bergeret

Giazotto²

2013

Phys. Rev. B

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We present an exhaustive study of the coherent heat transport through superconductor-ferromagnet (SF) Josephson junctions including a spin-filter (I sf ) tunneling barrier. By using the quasiclassical Keldysh Green's function technique we derive a general expression for the heat current flowing through a SF-I sf -FS junction and analyze the dependence of the thermal conductance on the spin-filter efficiency, the phase difference between the superconductors and the magnetization direction of the ferromagnetic layers. In the case of noncollinear magnetizations we show explicitly the contributions to the heat current stemming from the singlet and triplet components of the superconducting condensate. We also demonstrate that the magnetothermal resistance ratio of a SF-I sf -FS heat valve can be increased by the spin-filter effect under suitable conditions.

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Surface effects in magnetic superconductors with a spiral magnetic structure

Cited by 5 publications

References 33 publications

Nematic versus ferromagnetic spin filtering of triplet Cooper pairs in superconducting spintronics

Nematic versus ferromagnetic spin filtering of triplet Cooper pairs in superconducting spintronics

Enhanced triplet Andreev reflection off a domain wall in a lateral geometry

Phase-dependent heat transport through magnetic Josephson tunnel junctions

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