Proximity effect and interface transparency in Nb/Cu multilayers

Kushnir, V. N.; Prischepa, S. L.; Cirillo, C.; Attanasio, C.

doi:10.1063/1.3267868

Cited by 18 publications

(16 citation statements)

References 22 publications

(26 reference statements)

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“…7 and 11) have been reported. On the other hand, using the same experimental method described in this paper, we have recently obtained for a superconducting/normal metal system, namely Nb/Cu, a much smaller value for the specific boundary resistance, R B ¼ 0:33 fX m 2 24. It is also interesting to compare the values estimated in this work with those reported in the literature for similar S/F systems and obtained, again, using the CPP technique.…”

supporting

confidence: 76%

“…The parameter which has been added to the theory of the proximity effect to describe the strength of the interactions between two metals is the interface transparency coefficient, T , whose role has been extensively studied in the S/F, [7][8][9][10][11][12][13][14][15][16][17] as well as in the S/N case. [18][19][20][21][22][23][24] The role of the interface transparency in the theory is explicitly taken into account introducing the parameter c b R B =ðq F n F Þ. 25 c b describes the quality of the interface barrier, through the relation c b ¼ 2' F =ð3t F n F Þ.…”

Section: Introductionmentioning

confidence: 99%

“…A new experimental method has been recently developed to evaluate the parameter c b for S/N hybrids. 24 By simply measuring the dependence of T c on the Nb layer thickness, d S , in Cu/Nb/Cu trilayers and on the number of bilayers, N bil , in Cu/[Nb/Cu] N bil multilayers a value of 0.33 fX m 2 has been obtained for the specific resistance of the Nb/Cu interface, number which is in very good agreement with the value obtained using a more sophisticated technique based on current perpendicular-to-plane (CPP) measurements. 27 In this paper we extend the previous method to the more complex case of S/F hybrids.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Evaluation of the specific boundary resistance of superconducting/weakly ferromagnetic hybrids by critical temperature measurements

Mancusi

Ilyina

Kushnir

et al. 2011

Journal of Applied Physics

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Anomalous low temperature stair like coercivity decrease due to magnetostatic coupling between superconducting and ferromagnetic particles in mixed powders Dimensional crossover and flux pinning of decoupled Cu 50 Ni 50 ∕ Nb multilayers J. Appl. Phys. 103, 07C704 (2008); 10.1063/1.2829607Magnetization-orientation dependence of the superconducting transition temperature and magnetoresistance in the ferromagnet-superconductor-ferromagnet trilayer system

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supporting

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Evaluation of the specific boundary resistance of superconducting/weakly ferromagnetic hybrids by critical temperature measurements

Mancusi

Ilyina

Kushnir

et al. 2011

Journal of Applied Physics

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“…The Z parameter is related to the transmission coefficient τ = 1/ √ 1 + Z 2 of an interface. Transmission through interfaces has been investigated using the superconducting proximity effect (PE) [15,16,17,18] and the current perpendicular to plane magnetoresistance (CPP-MR) [19,20,21,22]. In these experiments oxide barriers can be excluded because of the preparation method, and the transmission coefficient should therefore represent the contribution from Fermi surface mismatch only.…”

Section: Discussionmentioning

confidence: 99%

Spin polarization versus lifetime effects at point contacts between superconducting niobium and normal metals

Tuuli

Gloos

2012

J. Phys.: Conf. Ser.

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Abstract. Point-contact Andreev reflection spectroscopy is used to measure the spin polarization of metals but analysis of the spectra has encountered a number of serious challenges, one of which is the difficulty to distinguish the effects of spin polarization from those of the finite lifetime of Cooper pairs. We have recently confirmed the polarization-lifetime ambiguity for NbCo and Nb-Cu contacts and suggested to use Fermi surface mismatch, the normal reflection due to the difference of Fermi wave vectors of the two electrodes, to solve this dilemma. Here we present further experiments on contacts between superconducting Nb and the ferromagnets Fe and Ni as well as the noble metals Ag and Pt that support our previous results. Our data indicate that the Nb -normal metal interfaces have a transparency of up to about 80% and a small, if not negligible, spin polarization. IntroductionWith the growing interest in spintronics, measuring the spin polarization P of a metal has become an important task [1]. Andreev reflection spectroscopy of point contacts has been suggested as an effective and versatile technique for measuring the polarization of metals in contact with a superconductor [2,3]. To extract the polarization, one analyses the measured differential resistance spectra with the help of a modified BTK model [4,5,6]. This method has been applied to a wide range of materials, delivering converging values for the spin polarization. The extracted P has a linear or parabolic dependence on the relative strength of the interface barrier Z, and the true value of the polarization P is measured in the Z = 0 limit. Unfortunately, this procedure has also encountered problems, including inadequately understood additional spectral features [7] and, most of all, the degeneracy of the results of the various BTK type models [8,9]. This applies especially when the polarization is low.We have recently demonstrated how difficult it is to distinguish the effects of polarization and finite lifetime of Cooper pairs in the spectra of Nb-Co and Nb-Cu contacts [10]. The finite lifetime of the Cooper pairs has been used to describe the spectra of non-magnetic contacts [11], but with few exceptions [8,9,12] it has not generally been applied to contacts with magnetic metals even though one should expect strong pair breaking in that case. Since spectra of both magnets and non-magnets can often be fitted rather well with the two models, we have suggested

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“…It informs how large a fraction of the incident electrical current is not transported through an interface. Reflection or transmission at metal interfaces has mainly been investigated with the help of superconducting proximity effect measurements [1,2,3,4] and the current perpendicular to the plane magnetoresistance (CPP-MR) studies [5,6,7,8] using thin films. Point-contact Andreev reflection spectroscopy offers a different approach to this problem and does not require thin-film samples.…”

mentioning

confidence: 99%

Normal reflection at superconductor - normal metal interfaces due to Fermi surface mismatch

Tuuli¹,

Gloos²

2012

J. Phys.: Conf. Ser.

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Abstract. Electrons can be reflected at an interface between two metals because of a dielectric barrier or different properties of the Fermi surface. Andreev reflection allows to directly measure normal reflection when one of the metals is a superconductor. We have investigated normal reflection at interfaces between non-magnetic normal metals and superconducting Nb (Tc = 9.2 K) and Al (Tc = 1.2 K). The distribution of the values of the relative strength of the interface barrier, Z, for a number of contacts of a specific metal combination shows a welldefined peak which can be attributed to Fermi surface mismatch. Our reflection coefficients are generally smaller than those predicted theoretically or those derived from proximity-effect studies of normal-superconductor bi-layers. IntroductionFor practical nanoscale applications, including spintronics, the quality of an interface matters. To develop new devices it is important to understand their properties. The normal reflection coefficient R, or the complementary transmission coefficient τ = 1 − R, is one of the parameters that characterizes an interface. It informs how large a fraction of the incident electrical current is not transported through an interface. Reflection or transmission at metal interfaces has mainly been investigated with the help of superconducting proximity effect measurements [1,2,3,4] and the current perpendicular to the plane magnetoresistance (CPP-MR) studies [5,6,7,8] using thin films. Point-contact Andreev reflection spectroscopy offers a different approach to this problem and does not require thin-film samples. It is a differential method as it compares the normal reflection of the two-particle electron -hole process to that of a single-particle one. Andreev reflection at a superconductor -normal metal interface is described by the BTK-model [9] with only three adjustable parameters: the energy gap of the superconductor 2∆, the temperature T which is measured independently, and the relative strength Z of a δ-function interface barrier. This simple model has been extended to take into account the effects of spin polarization [10,11] and the finite Cooper pair lifetime [12].It has been suggested [13] that the BTK Z parameter consists of two parts, Z b describing the strength of a real tunneling barrier at the contact and Z 0 the reflection caused by the mismatch of the different electronic structures on each side of the interface. The Z parameter is related to the transmission coefficient τ = 1/(1 + Z 2 ). Without tunneling barrier only Fermi surface mismatch contributes, providing a lower limit for the reflection coefficient of a specific metal -

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Proximity effect and interface transparency in Nb/Cu multilayers

Cited by 18 publications

References 22 publications

Evaluation of the specific boundary resistance of superconducting/weakly ferromagnetic hybrids by critical temperature measurements

Evaluation of the specific boundary resistance of superconducting/weakly ferromagnetic hybrids by critical temperature measurements

Spin polarization versus lifetime effects at point contacts between superconducting niobium and normal metals

Normal reflection at superconductor - normal metal interfaces due to Fermi surface mismatch

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