Periodic Reporting for period 1 - SUPERMINT (Interplay between Chirality, Spin Textures and Superconductivity at Manufactured Interfaces)
Reporting period: 2022-10-01 to 2025-03-31
SUPERMINT is an ambitious project exploring the interaction between some of the most ground-breaking recent discoveries in spintronics and superconductivity. SUPERMINT explores the interplay between chirality, spin texture and superconductivity. In the age of big data and the ongoing artificial intelligence revolution, there is an ever-growing need for large-scale storage and computing capabilities, which are highly energy-intensive. Spin-based technologies, such as magnetic random-access memory (MRAM) and magnetic Racetrack Memory (RTM), consume significant energy because spin currents are typically generated from electrical currents. In contrast, one of the unique features of superconductors is the dissipationless flow of supercurrents, meaning little to no energy is lost when current passes through superconducting materials. However, since the ground state of conventional superconductors is formed from spin-singlet Cooper pairs, magnetism and superconductivity are generally incompatible with one another. There has long been interest, however, in exotic superconducting materials where the spins in Cooper pairs align parallel to one another, allowing supercurrents to carry a net spin angular momentum.
A key objective of SUPERMINT is to leverage recent discoveries to create all the superconducting components required to develop SUPERTRACK—a high-performance, low-energy, non-volatile memory device that operates at cryogenic temperatures. In SUPERTRACK, digital data will be stored in a magnetic nanowire, much like in magnetic Racetrack Memory, but the writing, reading, and movement of magnetic bits will be driven by superconducting phenomena. SUPERMINT aims to achieve fundamental breakthroughs in our understanding of exotic superconductors, particularly in controlling spin direction and utilizing spin-polarized triplet supercurrents to manipulate the magnetic moments of nanoscale magnetic objects.
A key objective of SUPERMINT is to leverage recent discoveries to create all the superconducting components required to develop SUPERTRACK—a high-performance, low-energy, non-volatile memory device that operates at cryogenic temperatures. In SUPERTRACK, digital data will be stored in a magnetic nanowire, much like in magnetic Racetrack Memory, but the writing, reading, and movement of magnetic bits will be driven by superconducting phenomena. SUPERMINT aims to achieve fundamental breakthroughs in our understanding of exotic superconductors, particularly in controlling spin direction and utilizing spin-polarized triplet supercurrents to manipulate the magnetic moments of nanoscale magnetic objects.
1. Progress in SUPERTRACK:
Non-reciprocal supercurrent phenomena, including the Josephson and the superconducting diode effects (JDE/SDE), have generated significant interest due to their potential applications in energy-efficient cryogenic logic circuits. These non-reciprocal effects arise from mechanisms that include: (a) finite momentum pairing, (b) Rashba-like coupling, and (c) magnetic proximity interactions. Our research has been at the forefront of this field. During the first 2-year period of SUPERMINT, we have demonstrated a Josephson diode effect in 1T-PtTe_2, a type-II Dirac semimetal (P. Sivakumar et al. Commun. Phys. 7, 354 (2024)). This effect is facilitated by the material’s intrinsic helical spin-momentum locking and is distinct from extrinsic geometric factors. We also find correlation between the diode effect and the large 2nd-harmonic of the supercurrent. We have also introduced the concept of ‘tunable 2nd-order φ₀-junctions,’ where the relative phase between harmonic components can be modulated using a magnetic field.
A major goal of SUPERMINT is to demonstrate the manipulation of spin textures using triplet supercurrents. We have demonstrated the existence of triplet Cooper pairs in multilayer ferromagnetic vertical Josephson junctions (JJs) that includes metallic layers with large spin-orbit coupling. We have also demonstrated that spin-triplet Cooper pairs can be stabilized in non-collinear antiferromagnetic JJs.
2. Chirality Induced by Twisted Geometrical Structures:
Using advanced multi-photon lithography, we have fabricated 3D chiral magnetic ribbons with precisely controlled torsional chirality (clockwise or counter-clockwise) and variable magnitudes of twisting. Our experiments reveal new findings regarding the current-driven motion of chiral domain walls:
• The ability of domain walls to move along the ribbon depends critically on their intrinsic chirality and the geometrical torsion chirality of the structure.
• The interaction between magnetic exchange energy and torsional chirality induces a unique chiral torsion field, favoring chiral Bloch-type walls over the Néel-type walls preferred by the ribbon’s intrinsic magnetic properties.
Furthermore, we discovered a domain wall diode effect, where the motion of domain walls exhibits a non-reciprocal nature due to the interplay between spin chirality and geometrical torsion. This work has just been accepted for publication in Nature (A. Farinha et al. Nature (accepted)).
Non-reciprocal supercurrent phenomena, including the Josephson and the superconducting diode effects (JDE/SDE), have generated significant interest due to their potential applications in energy-efficient cryogenic logic circuits. These non-reciprocal effects arise from mechanisms that include: (a) finite momentum pairing, (b) Rashba-like coupling, and (c) magnetic proximity interactions. Our research has been at the forefront of this field. During the first 2-year period of SUPERMINT, we have demonstrated a Josephson diode effect in 1T-PtTe_2, a type-II Dirac semimetal (P. Sivakumar et al. Commun. Phys. 7, 354 (2024)). This effect is facilitated by the material’s intrinsic helical spin-momentum locking and is distinct from extrinsic geometric factors. We also find correlation between the diode effect and the large 2nd-harmonic of the supercurrent. We have also introduced the concept of ‘tunable 2nd-order φ₀-junctions,’ where the relative phase between harmonic components can be modulated using a magnetic field.
A major goal of SUPERMINT is to demonstrate the manipulation of spin textures using triplet supercurrents. We have demonstrated the existence of triplet Cooper pairs in multilayer ferromagnetic vertical Josephson junctions (JJs) that includes metallic layers with large spin-orbit coupling. We have also demonstrated that spin-triplet Cooper pairs can be stabilized in non-collinear antiferromagnetic JJs.
2. Chirality Induced by Twisted Geometrical Structures:
Using advanced multi-photon lithography, we have fabricated 3D chiral magnetic ribbons with precisely controlled torsional chirality (clockwise or counter-clockwise) and variable magnitudes of twisting. Our experiments reveal new findings regarding the current-driven motion of chiral domain walls:
• The ability of domain walls to move along the ribbon depends critically on their intrinsic chirality and the geometrical torsion chirality of the structure.
• The interaction between magnetic exchange energy and torsional chirality induces a unique chiral torsion field, favoring chiral Bloch-type walls over the Néel-type walls preferred by the ribbon’s intrinsic magnetic properties.
Furthermore, we discovered a domain wall diode effect, where the motion of domain walls exhibits a non-reciprocal nature due to the interplay between spin chirality and geometrical torsion. This work has just been accepted for publication in Nature (A. Farinha et al. Nature (accepted)).
The goal of SUPERMINT of developing a cryogenic computing technique based on the interplay of novel superconducting phenomena and nanoscopic magnetic textures has the potential to significantly impact future cryogenic memory-storage technologies. Currently, conventional computing systems suffer from the challenge of high energy consumption, which limits their efficiency and scalability. By focusing on creating highly energy efficient reading and writing processes of spin textures at cryogenic temperatures, our work could drastically reduce energy losses, making computing far more sustainable and efficient. From a fundamental scientific perspective, the demonstration of torques exhibited on magnetic spin textures at cryogenic temperatures via triplet supercurrents would be a major breakthrough.