Spin-Singlet and Spin-Triplet Josephson Junctions for Cryogenic Memory

Birge, Norman O.; Houzet, Manuel

doi:10.1109/lmag.2019.2955419

Cited by 19 publications

(9 citation statements)

References 31 publications

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“…Recent developments in superconducting spintronics involving combination of the magnetism and the superconductivity at the junction level have mitigated the power consumption problem. [15][16][17][18][19][20] However, the magnetic polarisation switching speed is restrained by the magnetic junction physics at cryogenic temperatures. Use of flux quantum in a superconducting loop to store data can match the speeds of SFQ circuits.…”

mentioning

confidence: 99%

Miniaturization of the Superconducting Memory Cell via a Three-Dimensional Nb Nano-superconducting Quantum Interference Device

Chen

Wang

et al. 2020

ACS Nano

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Scalable memories that can match the speeds of superconducting logic circuits have long been desired to enable a superconducting computer. A superconducting loop that includes a Josephson junction can store a flux quantum state in picoseconds. However, the requirement for the loop inductance to create a bi-state hysteresis sets a limit on the minimal area occupied by a single memory cell. Here, we present a miniaturized superconducting memory cell based on a Three-Dimensional (3D) Nb nano-Superconducting QUantum Interference Device (nano-SQUID). The major cell area here fits within an 8×9 μm 2 rectangle with a cross-selected function for memory implementation. The cell shows periodic tunable hysteresis between two neighbouring flux quantum states produced by bias current sweeping because of the large modulation depth of the 3D nano-SQUID (~66%). Furthermore, the measured Current-Phase Relations (CPRs) of nano-SQUIDs are shown to be skewed from a sine function, as predicted by theoretical modelling. The skewness and the critical current of 3D nano-SQUIDs are linearly correlated. It is also found that the hysteresis loop size is in a linear scaling relationship with the CPR skewness using the statistics from characterisation of 26 devices. We show that the CPR skewness range of π/4-3π/4 is equivalent to a large loop inductance in creating a stable bi-state hysteresis for memory implementation. Therefore, the skewed CPR of 3D nano-SQUID enables further superconducting memory cell miniaturization by overcoming the inductance limitation of the loop area.

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confidence: 99%

Miniaturization of the Superconducting Memory Cell via a Three-Dimensional Nb Nano-superconducting Quantum Interference Device

Chen

Wang

et al. 2020

ACS Nano

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“…Superconducting technologies based on Josephson junctions are a promising candidate for a low power computational alternative to traditional CMOS technologies [4,5]. Of particular interest, here, are ferromagnetic Josephson junctions which form the memory bits in such a scheme [6][7][8][9][10][11][12][13][14][15][16][17][18]. There have been numerous reports concerning the supercurrent passing through ferromagnetic Josephson junctions, including the discovery of spin triplet pair correlations in these systems [19][20][21][22][23][24][25][26].…”

Section: Introductionmentioning

confidence: 99%

Distortions to the penetration depth and coherence length of superconductor/normal-metal superlattices

Quarterman

Satchell

Kirby

et al. 2020

Phys. Rev. Materials

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Superconducting (S) thin film superlattices composed of Nb and a normal metal spacer (N) have been extensively utilized in Josephson junctions given their favorable surface roughness compared to Nb films of comparable thickness. In this work, we characterize the London penetration depth and Ginzburg-Landau coherence lengths of S /N superlattices using polarized neutron reflectometry and electrical transport. Despite the normal metal spacer layers being only approximately 8% of the total superlattice thickness, we surprisingly find that the introduction of these thin N spacers between S layers leads to a dramatic increase in the measured London penetration depth compared to that of a single Nb film of comparable thickness. Using the measured values for the effective inand out-of-plane coherence lengths, we quantify the induced anisotropy of the superlattice samples and compare to a single Nb film sample. From these results, we find that that the superlattices behave similarly to layered 2D superconductors.

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Section: Introductionmentioning

confidence: 99%

Distortions to the penetration depth and coherence length of superconductor/normal-metal superlattices

Quarterman,

Satchell,

Kirby

et al. 2020

Preprint

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Superconducting (S ) thin film superlattices composed of Nb and a normal metal spacer (N ) have been extensively utilized in Josephson junctions given their favorable surface roughness compared to Nb thin films of comparable thickness. In this work, we characterize the London penetration depth and Ginzburg-Landau coherence length of S /N superlattices using polarized neutron reflectometry and electrical transport. Despite the normal metal spacer layer being significantly thinner than the coherence length, we find that the introduction of a thin N spacer between S layers leads to a dramatic increase in the London penetration depth and a decrease in the coherence length. Furthermore, the temperature dependence of the upper critical field suggests that the superlattices act as a layered 2D superconductor, despite the N thickness being more than a factor of two smaller than when such a 2D state is expected to occur. Using the measured values for the penetration depth and coherence length, we experimentally determine the Ginzburg-Landau parameter to quantify the superconducting disorder of the superlattice samples and compare to a single Nb thin film sample.

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Spin-Singlet and Spin-Triplet Josephson Junctions for Cryogenic Memory

Cited by 19 publications

References 31 publications

Miniaturization of the Superconducting Memory Cell via a Three-Dimensional Nb Nano-superconducting Quantum Interference Device

Miniaturization of the Superconducting Memory Cell via a Three-Dimensional Nb Nano-superconducting Quantum Interference Device

Distortions to the penetration depth and coherence length of superconductor/normal-metal superlattices

Distortions to the penetration depth and coherence length of superconductor/normal-metal superlattices

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