Nonlinear thermoelectric effects in high-field superconductor-ferromagnet tunnel junctions

Kolenda, S.; Machon, Peter; Beckmann, D.; Belzig, Wolfgang

doi:10.3762/bjnano.7.152

Cited by 35 publications

(35 citation statements)

References 32 publications

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“…Its interface with a ferromagnetic metal results in a spin-polarized conductance leading to a large Seebeck effect. Following this principle, large spin-dependent TE effects have been theoretically proposed [2][3][4][5][6][7][8][9] and experimentally demonstrated [10][11][12] in spin-split and -polarized superconducting tunnel contacts [13]. Furthermore, TE properties in a variety of systems have been investigated [14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Spin-flip enhanced thermoelectricity in superconductor-ferromagnet bilayers

et al. 2018

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We study the effects of spin-splitting and spin-flip scattering in a superconductor (S) on the thermoelectric (TE) properties of a tunneling contact to a metallic ferromagnet (F) using the Green's function method. A giant thermopower has been theoretically predicted and experimentally observed in such structures. This is attributed to the spin-dependent particle-hole asymmetry in the tunneling density of states (DOS) in the S/F heterostructure. Here, we evaluate the S DOS and thermopower for a range of temperatures, Zeeman-splitting, and spin-flip scattering. In contrast to the naive expectation based on the negative effect of spin-flip scattering on Cooper pairing, we find that the spin-flip scattering strongly enhances the TE performance of the system in the low-field and lowtemperature regime. This is attributed to a complex interplay between the charge and spin conductances caused by the softening of the spin-dependent superconducting gaps. The maximal value of the thermopower exceeds k B /e by a factor of ≈5 and has a non-monotonic dependence on spin-splitting and spin-flip rate.

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Section: Introductionmentioning

confidence: 99%

Spin-flip enhanced thermoelectricity in superconductor-ferromagnet bilayers

et al. 2018

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“…Unfortunately, particle-hole symmetry is generally preserved in a superconductor and this leads to a perfect cancellation of the thermoelectric current due to counterpropagating electron and hole flows. The symmetry can be broken with external magnetic fields or spin-polarized bands [18], leading to sizable values of S as demonstrated both theoretically [19,20,21,22,23,24,25,26,27,28] and experimentally [29,30]. Another possibility is to drive the junction out of equilibrium beyond the linear response regime.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear electric and thermoelectric Andreev transport through a hybrid quantum dot coupled to ferromagnetic and superconducting leads

2017

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Abstract. We discuss the nonlinear Andreev current of an interacting quantum dot coupled to spinpolarized and superconducting reservoirs when voltage and temperature biases are applied across the nanostructure. Due to the particle-hole symmetry introduced by the superconducting (S) lead, the subgap spin current vanishes identically. Nevertheless, the Andreev charge current depends on the degree of polarization in the ferromagnetic (F) contact since the shift of electrostatic internal potential of the conductor depends on spin orientation of the charge carrier. This spin-dependent potential shift characterizes nonlinear responses in our device. We show how the subgap current versus the bias voltage or temperature difference depends on the lead polarization in two cases, namely (i) S-dominant case, when the dot-superconductor tunneling rate (ΓR) is much higher than the ferromagnet-dot tunnel coupling (ΓL), and (ii) F-dominant case, when ΓL ≫ ΓR. For the ferromagnetic dominant case the spin-dependent potential shows a nonmonotonic behavior as the dot level is detuned. Thus the subgap current can also exhibit interesting behaviors such as current rectification and the maximization of thermocurrents with smaller thermal biases when the lead polarization and the quantum dot level are adjusted.

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“…If we consider a locally spatially inhomogeneous magnetic texture like a domain wall (see figure 1(b)) the Riccati amplitudes ĝ and ĝ can be found from equation (17) numerically with the following asymptotic condition: Equation (17) is the normal Green's function, that is the upper left element in the particle-hole space of equation (16).…”

Section: Model and Methodsmentioning

confidence: 99%

Signatures of spin-triplet Cooper pairing in the density of states of spin-textured superconductor-ferromagnet bilayers

2019

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The existence of spin-triplet superconductivity in non-collinear magnetic heterostructures with superconductors is by now well established. This observation lays the foundation of superconducting spintronics with the aim to create a low-power consuming devices in order to replace the conventional electronics limited by heating. From a fundamental point of view the investigation of the structure and properties of spin-triplet Cooper pairs continues. Recently, spectroscopic evidence has shown to offer more detailed insights in the structure of triplet Cooper pairs than the supercurrent. Hence, we study here the structure of spin-triplet Cooper pairs through the density of states (DOS) in bilayers of a textured magnetic insulator in proximity to a superconductor. Using quasiclassical Green function methods, we study the local DOS, both spin-resolved and spin-independent. We show that the equalspin and mixed-spin triplet Cooper pairs leads to different spectroscopic signatures, which can be further enhanced by spin-polarized spectroscopy. Our results show the huge potential spin-polarized tunneling methods offer in characterizing unconventional superconductivity in heterostructures.

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Nonlinear thermoelectric effects in high-field superconductor-ferromagnet tunnel junctions

Cited by 35 publications

References 32 publications

Spin-flip enhanced thermoelectricity in superconductor-ferromagnet bilayers

Spin-flip enhanced thermoelectricity in superconductor-ferromagnet bilayers

Nonlinear electric and thermoelectric Andreev transport through a hybrid quantum dot coupled to ferromagnetic and superconducting leads

Signatures of spin-triplet Cooper pairing in the density of states of spin-textured superconductor-ferromagnet bilayers

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