Spin-polarized supercurrents for spintronics: a review of current progress

Eschrig, Matthias

doi:10.1088/0034-4885/78/10/104501

Cited by 531 publications

(524 citation statements)

References 454 publications

(812 reference statements)

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“…Note that in our case the phase jump of π occurs at y 0 ≈ 0.8λ, while in the case of the Pearls vortex in the ultrathin film the corresponding distance is [47] 2w × 0.175 = 0.35w. Note that the finite electron transparency of the insulation barrier should result in a small correction to κ on the order of (λ/λ J ) 2 and does not qualitatively influence further results.…”

Section: A Modelmentioning

confidence: 94%

“…Josephson junctions (JJs) with nonzero spontaneous phase difference between the superconducting electrodes in the ground state (the so-called π , ϕ 0 , and ϕ JJs) have become the subject of intensive theoretical and experimental study during the past decade [1,2]. The most striking feature of such junctions is their ability to generate a current in the superconducting circuit, thus acting as a phase battery [3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

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Anomalous Josephson effect controlled by an Abrikosov vortex

et al. 2017

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The possibility of a fast and precise Abrikosov vortex manipulation by a focused laser beam opens the way to create laser-driven Josephson junctions. We theoretically demonstrate that a vortex pinned in the vicinity of the Josephson junction generates an arbitrary ground state phase which can be equal not only to 0 or π but to any desired ϕ 0 value in between. Such ϕ 0 junctions have many peculiar properties and may be effectively controlled by the optically driven Abrikosov vortex. Also we theoretically show that the Josephson junction with the embedded vortex can serve as an ultrafast memory cell operating at sub THz frequencies. I. INTRODUCTIONJosephson junctions (JJs) with nonzero spontaneous phase difference between the superconducting electrodes in the ground state (the so-called π , ϕ 0 , and ϕ JJs) have become the subject of intensive theoretical and experimental study during the past decade [1,2]. The most striking feature of such junctions is their ability to generate a current in the superconducting circuit, thus acting as a phase battery [3][4][5][6]. In addition, relatively small variation of the system parameters may provoke dramatic changes in the ground state phase difference, which is believed to provide new effective tools for controlling the currents in microelectronic devices (see, e.g., Refs. [7,8]).There are several generic mechanisms leading to the spontaneous appearance of nonzero Josephson phase. The basic one reveals when the superconducting (S) electrodes are separated by a ferromagnetic (F) layer. The exchange field inside the ferromagnet produces the spatial oscillations of the Cooper pair wave function, and depending on the ratio between the oscillation period and the F-layer thickness the ground state phase is equal to 0 or π (these cases are referred as 0 or π JJs, respectively) [9][10][11]. A peculiar situation is realized when the thickness d of the ferromagnet varies along the junction in a way that in some parts of the ferromagnet the value of d corresponds to the 0 state while in other parts to the π state (see Ref. [12] and references therein). If there is only a slight difference between the areas of the "0" and "π " regions the phase frustration can result in the appearance of a state with the spontaneous phase difference φ = ±ϕ = 0,π which is degenerate (ϕ JJ) (see Ref.[13] and references therein). A similar effect takes place in Josephson junctions with the current injectors acting as an effective source of the phase jumps along the junction (see and references therein). One can also obtain a ϕ 0 JJ, where the ground state phase φ = ϕ 0 is not degenerate, e.g., using the JJs with broken inversion symmetry [17]. In this case the superconducting current I through the junction should not be necessarily an odd function of the phase difference φ and can take the form I = I c sin(φ + ϕ 0 ) [17]. Such situation is realized in the S|F|S junctions with strong spin-orbit coupling (see and references therein) or complicated noncollinear distribution of the magnetization (see an...

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Section: A Modelmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Anomalous Josephson effect controlled by an Abrikosov vortex

et al. 2017

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“…3 shows the energy profile of the system in the regime when the thickness d s is close to its critical value calculated from Eqs. (2,4). It is seen that there are two local minima at the phases ϕ = 0 and ϕ = π, which correspond to the 0-and SPD-states.…”

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confidence: 93%

Superconducting phase domains for memory applications

Bakurskiy

Klenov

Soloviev

et al. 2016

Applied Physics Letters

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In this work we study theoretically the properties of S-F/N-sIS type Josephson junctions in the frame of the quasiclassical Usadel formalism. The structure consists of two superconducting electrodes (S), a tunnel barrier (I), a combined normal metal/ferromagnet (N/F) interlayer and a thin superconducting film (s). We demonstrate the breakdown of a spatial uniformity of the superconducting order in the s-film and its decomposition into domains with a phase shift π . The effect is sensitive to the thickness of the s layer and the widths of the F and N films in the direction along the sIS interface. We predict the existence of a regime where the structure has two energy minima and can be switched between them by an electric current injected laterally into the structure. The state of the system can be non-destructively read by an electric current flowing across the junction. PACS numbers: 74.45.+c, 74.50.+r, 74.78.Fk, 85.25.Cp Josephson junctions containing normal (N) and ferromagnetic (F) materials in a weak link region are currently the subject of intense research. An interest in such structures is due to the possibility of their use as control elements of superconductor memory compatible with Single Flux Quantum (SFQ) logic. A number of implementations of Josephson control elements were proposed recently, among which the structures containing F layers in the weak link region are of greatest interest 1-3 . Various types of superconducting spin-valve structures including two or more ferromagnetic layers have been proposed [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] . The mutual orientations, parallel or antiparallel, of magnetizations of the layers determine critical currents and critical temperatures of the structures. Recently, it was proposed to apply the phenomenon of triplet superconductivity in spin-valve devices with noncollinear magnetization of the layers [19][20][21][22][23][24][25][26][27] . The problem of small characteristic voltage I C R N in these structures was solved by using an additional tunnel barrier connected through a thin superconducting spacer [28][29][30][31] . However, to control an operation of these devices, the application of magnetic fields or strong spin-polarized currents is necessary in order to switch the structure to a different state. Such control requires the use of additional external circuits resulting in restriction of possible memory density. Moreover, characteristic operational times of such devices are limited by relatively slow processes of the remagnetization of the ferromagnetic layers.In this work we propose a S-N/F-s-I-S control unit for a superconducting memory cell (Fig.1) based on the principles completely different as the suggested earlier. The considered structure consists of the two superconductive electrodes (S) and of the two weak link regions: the tunnel barrier (I) and the metallic (N/F) interlayer. The (N/F) part is formed by the longitudinally oriented normal (N) and ferromagnetic (F) layers. The weak link areas are separated by a thin super...

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“…Intuitively, one might expect stronger superconducting correlations to give rise to a stronger Meissner response of the normal metal. The modelling of such systems via quasiclassical theory largely confirms this picture [2], except the observation that the magnetic susceptibility has a puzzling re-entrant behavior as a function of temperature [3][4][5].When superconductors are placed in contact with ferromagnets, triplet Cooper pairs emerge that carry a net spin [6][7][8][9]. Such pairs are additionally characterized by an odd-frequency symmetry [10] which influences several physical properties, such as the electronic density of states and electromagnetic response.…”

mentioning

confidence: 95%

“…When superconductors are placed in contact with ferromagnets, triplet Cooper pairs emerge that carry a net spin [6][7][8][9]. Such pairs are additionally characterized by an odd-frequency symmetry [10] which influences several physical properties, such as the electronic density of states and electromagnetic response.…”

mentioning

confidence: 99%

Anisotropic Paramagnetic Meissner Effect by Spin-Orbit Coupling

2016

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Conventional s-wave superconductors repel external magnetic flux. However, a recent experiment [A. Di Bernardo et al., Phys. Rev. X 5, 041021 (2015)] has tailored the electromagnetic response of superconducting correlations via adjacent magnetic materials. We consider another route to alter the Meissner effect where spinorbit interactions induce an anisotropic Meissner response that changes sign depending on the field orientation. The tunable electromagnetic response opens new paths in the utilization of hybrid systems comprised of magnets and superconductors.Introduction. The Meissner effect in superconductors is the expulsion of magnetic fields and it is one of its two defining properties, the other being the absence of electrical resistance. Experiments have shown [1] that a non-superconducting material can also exhibit a Meissner response when it is in proximity to a superconductor. Via the proximity effect, superconducting correlations leak into the neighbouring metal. Intuitively, one might expect stronger superconducting correlations to give rise to a stronger Meissner response of the normal metal. The modelling of such systems via quasiclassical theory largely confirms this picture [2], except the observation that the magnetic susceptibility has a puzzling re-entrant behavior as a function of temperature [3][4][5].When superconductors are placed in contact with ferromagnets, triplet Cooper pairs emerge that carry a net spin [6][7][8][9]. Such pairs are additionally characterized by an odd-frequency symmetry [10] which influences several physical properties, such as the electronic density of states and electromagnetic response. Very recently, an experiment [11] observed a paramagnetic Meissner effect in an Nb/Ho/Au structure. In this system, superconductivity enhanced the magnetic signal rather than expelling it. Such a finding is of a fundamental interest, since it questions the hallmark property of perfect diamagnetism in superconductors. From a practical point of view, a paramagnetic Meissner effect could lead to an integration of magnetic and superconducting materials in a way that has not been possible previously. Moreover, the recent demonstration of remotely induced magnetism via a superconductor reported in Ref. [12] suggests that the study of how superconductivity influences magnetic signals is particularly timely.Motivated by these experimental advances, we show in this Letter that by combining superconductors with spin-orbit coupled materials, the Meissner effect can be modulated by the orientation of an external magnetic field. Not only does the Meissner response of the system become anisotropic as a function of field orientation, but it can even change sign. This offers a way to control the electromagnetic response of a superconducting system in situ. In addition, we demonstrate that magnetic exchange fields h that are much smaller than the superconducting gap ∆ 0 , e.g. induced via the Zeeman-effect of an external field, can lead to a similar re-entrant behavior of the susceptibility as in ...

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Spin-polarized supercurrents for spintronics: a review of current progress

Cited by 531 publications

References 454 publications

Anomalous Josephson effect controlled by an Abrikosov vortex

Anomalous Josephson effect controlled by an Abrikosov vortex

Superconducting phase domains for memory applications

Anisotropic Paramagnetic Meissner Effect by Spin-Orbit Coupling

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