A Boost for Superconducting Logic

Robinson, Jason W. A.

doi:10.1103/physics.8.49

Cited by 7 publications

(4 citation statements)

References 24 publications

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“…Indirect evidence for the generation of odd frequency triplet states has emerged from measurements of S/F/S Josephson junctions, which demonstrate a coherence length in F that is much longer than predicted for BCS (singlet) proximity effects 5 6 7 8 9 10 11 or in junctions with ferromagnetic insulators with high spin-polarizations 12 . Odd frequency triplet pairing has also been inferred from critical temperature measurements of S/F/F spin valves 13 14 15 16 17 18 19 . The superconducting excitation spectrum for the odd frequency triplet state should be gapless, meaning the net subgap DOS should be enhanced rather than suppressed 20 21 at certain energies (voltages).…”

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confidence: 99%

Signature of magnetic-dependent gapless odd frequency states at superconductor/ferromagnet interfaces

et al. 2015

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The theory of superconductivity developed by Bardeen, Cooper and Schrieffer (BCS) explains the stabilization of electron pairs into a spin-singlet, even frequency, state by the formation of an energy gap within which the density of states is zero. At a superconductor interface with an inhomogeneous ferromagnet, a gapless odd frequency superconducting state is predicted, in which the Cooper pairs are in a spin-triplet state. Although indirect evidence for such a state has been obtained, the gap structure and pairing symmetry have not so far been determined. Here we report scanning tunnelling spectroscopy of Nb superconducting films proximity coupled to epitaxial Ho. These measurements reveal pronounced changes to the Nb subgap superconducting density of states on driving the Ho through a metamagnetic transition from a helical antiferromagnetic to a homogeneous ferromagnetic state for which a BCS-like gap is recovered. The results prove odd frequency spin-triplet superconductivity at superconductor/inhomogeneous magnet interfaces.

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confidence: 99%

Signature of magnetic-dependent gapless odd frequency states at superconductor/ferromagnet interfaces

et al. 2015

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“…31 and demonstrated experimentally in Refs. 18,19,[32][33][34][35] . In this work we show that even for a single F layer, the tunneling spectra on the S side of an S-F bilayer show enhanced superconducting features along with an increase of Tc upon application of a magnetic field.…”

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Inverse proximity effect at superconductor-ferromagnet interfaces: Evidence for induced triplet pairing in the superconductor

et al. 2015

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Considerable evidence for proximity induced triplet superconductivity on the ferromagnetic side of a superconductor-ferromagnet (S-F) interface now exists; however, the corresponding effect on the superconductor side has hardly been addressed. We have performed scanning tunneling spectroscopy measurements on NbN superconducting thin films proximity coupled to the half-metallic ferromagnet La2/3Ca1/3MnO3 (LCMO) as a function of magnetic field. We have found that at zero and low applied magnetic fields the tunneling spectra on NbN typically show an anomalous gap structure with suppressed coherence peaks and, in some cases, a zerobias conductance peak. As the field increases to the magnetic saturation of LCMO where the magnetization is homogeneuous, the spectra become more BCS-like and the critical temperature of the NbN increases, implying a reduced proximity effect. Our results therefore suggest that triplet-pairing correlations are also induced in the S side of an S-F bilayer.(a)

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“…Recently, a triplet SSV was employed to induce magnetism into a normal conducting metal [ 60 ]. Triplet SSVs are expected to perform logical functions like the normal conducting giant magnetoresistance (GMR) devices, however, with a much better energy efficiency [ 61 ].…”

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confidence: 99%

Thickness dependence of the triplet spin-valve effect in superconductor–ferromagnet–ferromagnet heterostructures

Lenk¹,

Zdravkov²,

Kehrle³

et al. 2016

Beilstein J. Nanotechnol.

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Summary Background: In nanoscale layered S/F1/N/F2/AF heterostructures, the generation of a long-range, odd-in-frequency spin-projection one triplet component of superconductivity, arising at non-collinear alignment of the magnetizations of F1 and F2, exhausts the singlet state. This yields the possibility of a global minimum of the superconducting transition temperature T c, i.e., a superconducting triplet spin-valve effect, around mutually perpendicular alignment. Results: The superconducting triplet spin valve is realized with S = Nb a singlet superconductor, F1 = Cu41Ni59 and F2 = Co ferromagnetic metals, AF = CoOx an antiferromagnetic oxide, and N = nc-Nb a normal conducting (nc) non-magnetic metal, which serves to decouple F1 and F2. The non-collinear alignment of the magnetizations is obtained by applying an external magnetic field parallel to the layers of the heterostructure and exploiting the intrinsic perpendicular easy-axis of the magnetization of the Cu41Ni59 thin film in conjunction with the exchange bias between CoOx and Co. The magnetic configurations are confirmed by superconducting quantum interference device (SQUID) magnetic moment measurements. The triplet spin-valve effect has been investigated for different layer thicknesses, d F1, of F1 and was found to decay with increasing d F1. The data is described by an empirical model and, moreover, by calculations using the microscopic theory. Conclusion: The long-range triplet component of superconducting pairing is generated from the singlet component mainly at the N/F2 interface, where the amplitude of the singlet component is suppressed exponentially with increasing distance d F1. The decay length of the empirical model is found to be comparable to twice the electron mean free path of F1 and, thus, to the decay length of the singlet component in F1. Moreover, the obtained data is in qualitative agreement with the microscopic theory, which, however, predicts a (not investigated) breakdown of the triplet spin-valve effect for d F1 smaller than 0.3 to 0.4 times the magnetic coherence length, ξF1.

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A Boost for Superconducting Logic

Cited by 7 publications

References 24 publications

Signature of magnetic-dependent gapless odd frequency states at superconductor/ferromagnet interfaces

Signature of magnetic-dependent gapless odd frequency states at superconductor/ferromagnet interfaces

Inverse proximity effect at superconductor-ferromagnet interfaces: Evidence for induced triplet pairing in the superconductor

Thickness dependence of the triplet spin-valve effect in superconductor–ferromagnet–ferromagnet heterostructures

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