Quasiclassical free energy of superconductors: Disorder-driven first-order phase transition in superconductor/ferromagnetic-insulator bilayers

Virtanen, Pauli; Vargunin, Artjom; Силаев, М. А.

doi:10.1103/physrevb.101.094507

Cited by 12 publications

(4 citation statements)

References 70 publications

(137 reference statements)

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“…Although the splitting h in the ballistic model depends on the momentum direction, it is expected to be averaged by disorder of the bulk and the interface, and by Fermi liquid interactions [24,26,31,42]. For thin films, in this case one expects [26] h…”

Section: Non-reciprocal Transport In Hybrid Superconductor/ Ferromagn...mentioning

confidence: 99%

Superconductor-ferromagnet hybrids for non-reciprocal electronics and detectors

Geng,

Hijano,

Ilić

et al. 2023

Supercond. Sci. Technol.

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We review the use of hybrid thin films composed of superconductors and ferromagnets for creating non-reciprocal electronic components and self-biased detectors of electromagnetic radiation. We begin by introducing the theory behind these effects, as well as discussing various potential materials that can be used in the fabrication of these components. We then proceed with a detailed discussion on the fabrication and characterization of Al/EuS/Cu and EuS/Al/Co-based detectors, along with their noise analysis. Additionally, we suggest some approaches for multiplexing such self-biased detectors.

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Section: Non-reciprocal Transport In Hybrid Superconductor/ Ferromagn...mentioning

confidence: 99%

Superconductor-ferromagnet hybrids for non-reciprocal electronics and detectors

Geng,

Hijano,

Ilić

et al. 2023

Supercond. Sci. Technol.

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“…Namely, Tokuyasu et al [26] have shown that in the clean limit, this phase transition is always of the second order. However, a recent work established that even a small amount of impurity scattering restores the possibility of a first-order phase transition [43]. We assume here the diffusive limit, which is well justified for Al films due to their intrinsic disorder.…”

Section: Critical Temperature Of a Fi/s Bilayermentioning

confidence: 99%

Coexistence of superconductivity and spin-splitting fields in superconductor/ferromagnetic insulator bilayers of arbitrary thickness

Hijano,

Ilić,

Rouco

et al. 2020

Preprint

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Ferromagnetic insulators (FI) can induce a strong exchange field in an adjacent superconductor (S) via the magnetic proximity effect. This manifests as spin-splitting of the BCS density of states of the superconductor, an important ingredient for numerous superconducting spintronics applications and the realization of Majorana fermions. A crucial parameter that determines the magnitude of the induced spin-splitting in FI/S bilayers is the thickness of the S layer d: In very thin samples, the superconductivity is suppressed by the strong magnetism. By contrast, in very thick samples, the spin splitting is absent at distances away from the interface. In this work, we calculate the density of states and critical field of FI/S bilayers of arbitrary thickness. From here, we determine the range of parameters of interest for applications, where the exchange field and superconductivity coexist. We show that for d > 3.0ξs, the paramagnetic phase transition is always of the second order, in contrast to the first-order transition in thinner samples at low temperatures. Here ξs is the superconducting coherence length. Finally, we compare our theory with the tunneling spectroscopy measurements in several EuS/Al/AlOx/Al samples. If the Al film in contact with the EuS is thinner than a certain critical value, we do not observe superconductivity, whereas, in thicker samples, we find evidence of a first-order phase transition induced by an external field. The complete transition is preceded by a regime in which normal and superconducting regions coexist. We attribute this mixed phase to inhomogeneities of the Al film thickness and the presence of superparamagnetic grains at the EuS/Al interface with different switching fields. The step-like evolution of the tunnel-barrier magnetoresistance supports this assumption. Our results demonstrate on the one hand, the important role of the S layer thickness, which is particularly relevant for the fabrication of high-quality samples suitable for applications. On the other hand, the agreement between theory and experiment demonstrates the accuracy of our theory, which, originally developed for homogeneous situations, is generalized to highly inhomogeneous systems.

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“…This can be achieved, for example, in EuS/Al systems [2,4,5,7,24], where the interfacial exchange interaction leads to a sharp spin-splitting in S layers with thicknesses smaller than the coherent length. On the theoretical side, the effect of the interfacial exchange field and the induced spin-splitting on the superconducting state has been studied in numerous works [5,[25][26][27]. Most of these works assume a homogeneous spin-splitting field.…”

Section: Introductionmentioning

confidence: 99%

Quasiparticle density of states and triplet correlations in superconductor/ferromagnetic-insulator structures across a sharp domain wall

2022

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A ferromagnetic insulator (FI) in contact with a superconductor (S) is known to induce a spin splitting of the BCS density of states at the FI/S interface. This spin splitting causes the Cooper pairs to reduce their singlet-state correlations and acquire odd-in-frequency triplet correlations. We consider a diffusive FI/S bilayer with a sharp magnetic domain wall in the FI, and we study the local quasiparticle density of states and triplet superconducting correlations. In the case of collinear alignment of the domains, we obtain analytical results by solving the Usadel equation. For a small enough exchange field or weak superconductivity, we also find an analytical expressions for arbitrary magnetic textures, which reveals how the triplet component vector depends on the local magnetization of the FI. For an arbitrary angle between the magnetizations and the strength of the exchange field, we numerically solve the problem of a sharp domain wall. We finally propose two different setups based on FI/S/F stacks, where F is a ferromagnetic layer, to filter out singlet pairs and detect the presence of triplet correlations via tunneling differential conductance measurements.

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Quasiclassical free energy of superconductors: Disorder-driven first-order phase transition in superconductor/ferromagnetic-insulator bilayers

Cited by 12 publications

References 70 publications

Superconductor-ferromagnet hybrids for non-reciprocal electronics and detectors

Superconductor-ferromagnet hybrids for non-reciprocal electronics and detectors

Coexistence of superconductivity and spin-splitting fields in superconductor/ferromagnetic insulator bilayers of arbitrary thickness

Quasiparticle density of states and triplet correlations in superconductor/ferromagnetic-insulator structures across a sharp domain wall

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