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

Abstract

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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• Angular dependence of superconductivity in superconductor / spin valve heterostructures
• Spin Triplet Supercurrent in Co/Ni Multilayer Josephson Junctions with Perpendicular Anisotropy
• Anomalous double peak structure in Nb/Ni superconductor/ferromagnet tunneling DOS
• Spectroscopy and critical temperature of diffusive superconducting/ferromagnetic hybrid structures with spin-active interfaces
• Proximity-induced density-of-states oscillations in a superconductor/strong-ferromagnet system

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• In-gap features in superconducting LaAlO${}_3$-SrTiO${}_3$ interfaces observed by tunneling spectroscopy
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• Proximity-Induced Mixed Odd and Even Frequency Pairings in Monolayer NbSe${}_2$
• Exciting odd frequency equal-spin-triplet correlations at metal-superconductor interfaces
• Electromagnetic Proximity Effect: Superconducting Magnonics and Beyond
• Symmetry analysis of odd- and even-frequency superconducting gap symmetries for time-reversal symmetric interactions
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• Long-range triplet proximity effect in multiply connected ferromagnet-superconductor hybrids
• Induced odd-frequency superconducting state in vertex-corrected Eliashberg theory
• Effects of Rashba-spin-orbit coupling on superconducting boron-doped nanocrystalline diamond films: evidence of interfacial triplet superconductivity
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• Influence of electron-phonon coupling strength on signatures of even and odd-frequency superconductivity
• Signatures of superconducting triplet pairing in Ni--Ga-bilayer junctions
• Quasiparticle interference as a direct experimental probe of bulk odd-frequency superconducting pairing
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