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

Bernardo, Angelo Di; Diesch, Simon; Gu, Yuanzhou; Linder, Jacob; Divitini, Giorgio; Ducati, Caterina; Scheer, Elke; Blamire, M. G.; Robinson, J. W. A.

doi:10.1038/ncomms9053

Cited by 150 publications

(151 citation statements)

References 41 publications

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“…This behaviour is quite different to its neighbour in the periodic table holmium, which in thin films saturates in-plane at fields of typically only 300 mT, after which the squareness of its hysteresis loop suggest a long-ranged ferromagnetic ordering takes over and spiral magnetism does not reform [18,20]. This difference is most likely due to the c-axis crystalline anisotropy in the hcp structure being more important, or certainly being retained to a greater extent, in thin film Er.…”

Section: Magnetic Characterisationcontrasting

confidence: 65%

Probing the spiral magnetic phase in 6 nm textured erbium using polarised neutron reflectometry

Satchell

Witt

Burnell

et al. 2016

J. Phys.: Condens. Matter

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We characterise the magnetic state of highly-textured, sputter deposited erbium for a film of thickness 6 nm. Using polarised neutron reflectometry it is found the film has a high degree of magnetic disorder, and we present some evidence that the films' local magnetic state is consistent with bulk-like spiral magnetism. This, combined with complementary characterisation techniques, show that thin film erbium is a strong candidate material for incorporation into device structures.

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Section: Magnetic Characterisationcontrasting

confidence: 65%

Probing the spiral magnetic phase in 6 nm textured erbium using polarised neutron reflectometry

Satchell

Witt

Burnell

et al. 2016

J. Phys.: Condens. Matter

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“…In addition to theoretical studies, there are experimental indications of the realization of odd-ω pairing at the interface of Nb thin films and epitaxial Ho 25 . Furthermore, the concept of odd-ω order parameters can be generalized to charge and spin density waves 26,27 and Majorana fermion pairs 28 , demonstrating the pervasiveness of the odd-ω class of ordered states.…”

Section: Introductionmentioning

confidence: 99%

Pair symmetry conversion in driven multiband superconductors

Triola

Balatsky

2017

Phys. Rev. B

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It was recently shown that odd-frequency superconducting pair amplitudes can be induced in conventional superconductors subjected to a spatially nonuniform time-dependent drive. It has also been shown that, in the presence of interband scattering, multiband superconductors will possess bulk odd-frequency superconducting pair amplitudes. In this work we build on these previous results to demonstrate that by subjecting a multiband superconductor with interband scattering to a timedependent drive even-frequency pair amplitudes can be converted to odd-frequency pair amplitudes and vice versa. We will discuss the physical conditions under which these pair symmetry conversions can be achieved and possible experimental signatures of their presence.

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“…[34]. Even though signals for the experimental verification of odd-frequency states are often discussed in connection to systems which explicitly break time-reversal symmetry [31][32][33], our paper reveals that odd-frequency solutions do not require a time-reversal breaking potential. Oddfrequency solutions can arise naturally for a time-reversal symmetric interaction as a symmetry-breaking ground state of a many-particle system with time-reversal invariant interactions.…”

Section: Resultsmentioning

confidence: 95%

“…Also, odd-frequency states were discussed in connection to time-reversal topological superconductivity in double Rashba wires, where it was found that odd-frequency pairing is strongly enhanced in the topological state [30]. For some of the above mentioned systems, the respective signatures of odd-frequency correlations could also be verified experimentally [31][32][33][34]. An extensive discussion of edge-states and topology in superconductors including odd-frequency gap functions was communicated by Tanaka, Sato and Nagaosa [35].…”

mentioning

confidence: 94%

Symmetry analysis of odd- and even-frequency superconducting gap symmetries for time-reversal symmetric interactions

Geilhufe

Balatsky

2018

Phys. Rev. B

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Odd-frequency superconductivity describes a class of superconducting states where the superconducting gap is an odd function in relative time and Matsubara frequency. We present a group theoretical analysis based on the linearized gap equation in terms of Shubnikov groups of the second kind. By discussing systems with spin-orbit coupling and an interaction kernel which is symmetric under the reversal of relative time, we show that both even-and odd-frequency gaps are allowed to occur. Specific examples are discussed for the square lattice, the octahedral lattice, and the tetragonal lattice. For irreducible representations that are even under reversal of relative time the common combinations of s-and d-wave spin singlet and p-wave spin triplet gaps are revealed, irreducible representations that are odd under reversal of relative time give rise to s-and d-wave spin triplet and p-wave spin singlet gaps. Furthermore, we discuss the construction of a generalized GinzburgLandau theory in terms of the associated irreducible representations. The result complements the established classification of superconducting states of matter. [7]; and the organic superconductors like the BEDT-TTF-based charge transfer salts [8][9][10][11][12] exhibit symmetries of the superconducting gap beyond the conventional BCS s-wave [13]. In this connection, a group theory analysis based on the underlying symmetry of the pairing potential is crucial in establishing an unified classification of the arising superconducting states of matter [14][15][16][17][18][19]. In general, the pairing wave function of two electrons has to be anti-symmetric under particle interchange leading to the Pauli-principle. At equal times, and by neglecting orbital degrees of freedom two cases can occur: first, a gap odd in spin and even in parity, such as spin singlet s-and d-wave gaps, and, second, a gap even in spin and odd in parity, such as spin triplet p-and f -wave gaps.However, as pointed out by Berezinskii [20] and Balatsky and Abrahams [21] a pairing of particles beyond the conventional ones is possible, if the particle-particle correlator is zero at equal times but non-zero otherwise. This is achieved when the superconducting gap is an odd function in relative time, leading to the notion of odd-time or odd-frequency superconductivity, respectively (odd-frequency also refers to gap functions odd in Matsubara frequency). Among others, odd-frequency contributions were reported to occur in connection to diffusive ferromagnet/superconductor junctions [22,23] [28,29]. Also, odd-frequency states were discussed in connection to time-reversal topological superconductivity in double Rashba wires, where it was found that odd-frequency pairing is strongly enhanced in the topological state [30]. For some of the above mentioned systems, the respective signatures of odd-frequency correlations could also be verified experimentally [31][32][33][34]. An extensive discussion of edge-states and topology in superconductors including odd-frequency gap functions was communicat...

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

Cited by 150 publications

References 41 publications

Probing the spiral magnetic phase in 6 nm textured erbium using polarised neutron reflectometry

Probing the spiral magnetic phase in 6 nm textured erbium using polarised neutron reflectometry

Pair symmetry conversion in driven multiband superconductors

Symmetry analysis of odd- and even-frequency superconducting gap symmetries for time-reversal symmetric interactions

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