Strain-engineered long-distance supercurrent in an altermagnetic CrSb based-Josephson junction

arXiv:2610.11341 · cond-mat.supr-con · Submitted 2026-10-08 · Read on arXiv

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Introduction to the show: ident: Quantum Radio. Generated commentary on the latest quantum physics and condensed matter papers.

Kai: Today's paper: "Strain-engineered long-distance supercurrent in an altermagnetic CrSb based-Josephson junction".

Mira: The gist: The researchers demonstrate long-distance Josephson supercurrent transport through an epitaxial thin film of strained altermagnetic CrSb, exceeding conventional spin-singlet coherence length by nearly two orders of magnitude.

Kai: First, who's behind it and why it matters.

Title and authors: Mira: It seems the title itself sets up the whole idea: using strain to engineer these long-distance currents in an altermagnet junction. It’s not just about finding a superconductor; it's about using crystal structure manipulation to change how the quantum particles behave.

Kai: That’s right. The key here is that they are focusing on CrSb, which is an altermagnet, and they are using strain as the primary tool to unlock this long-distance transport.

Lev: I see the focus on strain engineering, but I want to understand what that means physically for a real device. Is it just about growing it in a specific way?

Mira: It’s more than just growth; it’s about introducing that uniform lattice mismatch between CrSb and an Al2O3 substrate. This strain shifts the crystal structure significantly, which then has downstream effects on the electronic properties, specifically opening up new pathways for spin correlations.

Kai: So they are using physical stress to induce a symmetry breaking in the material itself, which is what lets them get past the usual limits of singlet pairing.

The paper's summary: Kai: The summary explains that conventional superconductors only have singlet Cooper pairs, but this strain-engineered altermagnet junction allows these singlets to convert into spin-triplet correlations over a distance nearly two orders of magnitude larger than the singlet coherence length.

Mira: That’s the core finding. They suggest that the momentum-dependent spin splitting in this specific type of altermagnet acts like a spin mixing field, converting those initial singlet pairs into a triplet state, specifically ten correlations <ref:2610.11341#pg1>.

Lev: If that conversion happens, how does that help us with error correction? Can we actually use these triplet states to build more robust qubits or better memory?

Kai: It opens up the possibility of simulating spin-polarized triplet Cooper pairs and even things like finite-momentum Fulde–Ferrell–Larkin–Ovchinnikov states, which have real potential for dissipationless superconducting electronics.

The paper's improvements: Mira: The authors point out that the main improvement here is moving away from conventional ferromagnetic interlayers, which introduce stray fields that mess everything up. They replace them with altermagnets to eliminate those magnetic obstacles entirely.

Kai: They also highlighted how strain-induced spin-orbit coupling acts as a subsequent step, taking that initial triplet correlation and rotating it into equal-spin components like eleven or one which is what sustains the long-distance supercurrent <ref:2610.11341#pg1>.

Lev: That rotation sounds like a very clever way to protect the Cooper pairs from external magnetic noise or imperfections in the material structure. It’s essentially creating a symmetry protection mechanism for the pairing itself.

Conclusion: Kai: So, to wrap up, this paper on strain-engineered long-distance supercurrent in an altermagnetic CrSb based Josephson junction shows that we can get dissipationless transport over distances far exceeding the conventional singlet coherence limit by using strain to induce spin-triplet pairing.

Mira: It establishes altermagnets as a new platform because you get this long-range transport without all the stray field problems you usually have with conventional ferromagnets.

Lev: For me, it’s exciting because if we can model and predict these spin-polarized triplet Cooper pairs, it gives us a blueprint for designing dissipationless superconducting electronics that might be much more robust than what we currently build.

Kai: We’ll keep an eye on how they use this strain engineering to design novel spintronic devices that remove those barriers you mentioned earlier.

Mira: And the next thing we look at is how this mechanism relates to other quantum phenomena, setting the stage for even more complex superconducting applications.

Frontier Institute of Chip and System, Fudan University, Shanghai 200433, China · Shanghai Institute of Microsystem and Information Technology, ShanghaiTech University, Shanghai 201210, China · Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China · State Key laboratory of quantum functional materials, Department of Physics, and Guangdong Basic Research Center of Excellence for Quantum Science, Southern University of Science and Technology (SUSTech), Shenzhen 518055, China · Department of Physics, Fudan University, Shanghai 200433, China · State Key Laboratory of Surface Physics and Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai 200433, China · Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (Guangdong), Shenzhen 518045, China · School of Physics, Nankai University, Tianjin 300071, China · Interdisciplinary Center for Theoretical Physics and Information Sciences (ICTPIS), Fudan University, Shanghai 200433, China · International Center for Quantum Materials, Peking University, Beijing 100871, China · Hefei National Laboratory, Hefei 230088, China

cond-mat.supr-con

Submitted: 2026-10-08

Updated: 2026-10-08

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 83/100

The gist: The gist: The researchers demonstrate long-distance Josephson supercurrent transport through an epitaxial thin film of strained altermagnetic CrSb, exceeding conventional spin-singlet coherence

Key concepts

Altermagnets: These materials have a unique magnetic structure without macroscopic magnetization, unlike conventional ferromagnets. This absence of stray fields is crucial because it eliminates the disruptive stray magnetic fields that typically hinder conventional superconducting devices, allowing for cleaner exploration of unconventional superconductivity.
Momentum-dependent spin splitting: The gwave altermagnet possesses a momentum-dependent spin polarization. This acts as an effective 'spinmixing field' that converts standard singlet Cooper pairs into triplet correlations. This intrinsic property is key to generating the long-distance spin-triplet pairs necessary for the observed supercurrent.
Strain Engineering: Applying strain via lattice mismatch between CrSb and Al2O3 substrates modifies the crystal structure, specifically increasing the lattice constant along the c-axis by about 2.4%. This structural change is vital because it induces spin-orbit coupling effects that rotate the triplet component into states immune to magnetic moments, protecting the superconducting pairs.

Terminology

Altermagnets — 16× in this paper · explained in 1 episode
Coherence Length — 5× in this paper · explained in 2 episodes
Symmetry Breaking — 4× in this paper · explained in 3 episodes
Alignment — 1× in this paper · explained in 1 episode
Altermagnetic Spin Splitting — 1× in this paper · explained in 1 episode
Antiferromagnetism — 1× in this paper · explained in 1 episode
Degeneracy — 1× in this paper · explained in 3 episodes
Hysteresis — 1× in this paper · explained in 3 episodes

Summary

The gist: The researchers demonstrate long-distance Josephson supercurrent transport through an epitaxial thin film of strained altermagnetic CrSb, exceeding conventional spin-singlet coherence length by nearly two orders of magnitude.

Altermagnets as a Novel Platform

Altermagnets offer a unique platform for realizing unconventional superconducting states without the detrimental stray fields associated with conventional ferromagnets The absence of macroscopic magnetization substantially suppresses stray magnetic fields, while the intrinsic momentum-dependent spin polarization provides a natural route toward unconventional superconducting correlations analogous to ferromagnets This contrasts with conventional ferromagnets where spontaneous magnetization produces macroscopic stray fields that can induce screening currents and Abrikosov vortex formation in neighboring superconducting electrodes.

Strain Engineering and Structural Characterization

The high structural quality of the epitaxial films is confirmed by atomic-scale characterization, including molecular beam epitaxy (MBE) growth The lattice mismatch between CrSb and Al2O3 substrates introduces a uniform yet substantial strain into the CrSb lattice. X-ray diffraction (XRD) measurements reveal distinct diffraction peaks corresponding to the pristine CrSb, which shift from 32.13◦ to 31.35◦ under strain induced lattice expansion. This peak shift indicates that the lattice constant along the c-axis increases from ∼ 0.2784 nm to ∼ 0.2851 nm calculated using Bragg’s law, leading to a relatively strong lattice expansion of δc/cinitial ≈ 2.4%. Furthermore, the anomalous Hall measurement under an applied magnetic field in strained CrSb exhibits a finite anomalous Hall response that qualitatively follows the magnetic hysteresis behavior, providing evidence for strain-induced symmetry breaking and the emergence of spin-orbit coupling effect.

Mechanism for Long-Distance Supercurrent

The observation of Josephson transport over a length scale far exceeding the singlet coherence limit strongly suggests the generation of long-distance spin-triplet Cooper pairs in the altermagnetic CrSb junction. The momentum-dependent spin splitting inherent to the gwave altermagnet acts as an effective spinmixing field, converting injected singlet Cooper pairs 00⟩ from the Nb electrodes into 10⟩ triplet correlations. Subsequently, strain-induced spin-orbit coupling enables spin rotation from the triplet component 10⟩ into equal-spin components 11⟩ (or ¯11) triplet state, persisting over a long distance about two orders of magnitude larger than the spin singlet Cooper pair and leading to a detectable Josephson supercurrent.

Experimental Evidence of Superconductivity

The strained CrSb device exhibits a pronounced superconducting transition below T ≈ 0.55 K, whereas the pristine CrSb junction does not show comparable zero-resistance transport. The current–voltage (I – V) curve of the CrSb Josephson junction at various temperatures displays a clear Josephson signature, featuring a zero-voltage branch at low bias currents and a temperature-dependent switching current. The differential resistance map R(B, I) of the strained CrSb junction shows a clear periodic modulation with a central maximum around B ≈ 0 and nodes near B ≈ ±4 mT, which is a characteristic fingerprint of spatial phase coherence in Josephson junctions.

Conclusion and Outlook

The combination of zero-resistance transport, magnetic-field-induced Josephson interference, and strain-dependent symmetry breaking provides possible evidence for unconventional triplet-mediated superconducting transport in altermagnets. This approach removes the outstanding obstacles of stray fields and complex multilayer engineering in superconducting spintronics. Our findings establish altermagnets as a new material platform for scalable superconducting spintronics, enabling future exploration of phase-controllable Josephson devices, superconducting diodes, and triplet-based superconducting quantum interference technologies. The momentum-dependent spin splitting inherent to the gwave altermagnetic order acts as an effective spinmixing field. The strain-induced symmetry breaking further activates spin-orbit coupling effects, which rotate the 10⟩ triplet component into equal-spin triplet states ¯11> or ¯1−1) making the Cooper-pairs immune to the magnetic moments. This mechanism is conceptually related to the Bergeret–Volkov–Efetov theory developed for superconductor/ferromagnet/superconductor junctions. The absence of macroscopic stray field, combined with symmetry-protected momentum-dependent spin splitting, provides an ideal platform for exploring unconventional superconducting proximity effects free from the magnetic-field background associated with ferromagnets. This could give rise to an unexplored superconducting diode effect. The supercurrent observed in this work provides a strong impetus for further investigations into altermagnetic superconductivity. The observation of Josephson transport over a length scale far exceeding the singlet coherence limit strongly suggests the generation of long-distance spin-triplet Cooper pairs in the altermagnetic CrSb junction. The combination of zero-resistance transport, magnetic-field-induced Josephson interference, and strain-dependent symmetry breaking provides possible evidence for unconventional triplet-mediated superconducting transport in altermagnets. By replacing ferromagnetic interlayers with altermagnets, our approach removes the outstanding obstacles of stray fields and complex multilayer engineering in superconducting spintronics. The momentum-dependent spin splitting inherent to the gwave altermagnetic order acts as an effective spinmixing field, converting injected singlet Cooper pairs 00⟩ from the Nb electrodes into 10⟩ triplet correlations. Subsequently, strain-induced spin-orbit coupling enables spin rotation from the triplet component 10⟩ into equal-spin components ¯11> (or ¯1−1) making the Cooper-pairs immune to the magnetic moments. This mechanism is conceptually related to the Bergeret–Volkov–Efetov theory developed for superconductor/ferromagnet/superconductor junctions. The absence of macroscopic stray field, combined with symmetry-protected momentum-dependent spin splitting, provides an ideal platform for exploring unconventional superconducting proximity effects free from the magnetic-field background associated with ferromagnets. This could give rise to an unexplored superconducting diode effect. The supercurrent observed in this work provides a strong impetus for further investigations into altermagnetic superconductivity. The observation of Josephson transport over a length scale far exceeding the singlet coherence limit strongly suggests the generation of long-distance spin-triplet Cooper pairs in the altermagnetic CrSb junction. The combination of zero-resistance transport, magnetic-field-induced Josephson interference, and strain-dependent symmetry breaking provides possible evidence for unconventional triplet-mediated superconducting transport in altermagnets. By replacing ferromagnetic interlayers with altermagnets, our approach removes the outstanding obstacles of stray fields and complex multilayer engineering in superconducting spintronics. The momentum-dependent spin splitting inherent to the gwave altermagnetic order acts as an effective spinmixing field, converting injected singlet Cooper pairs 00⟩ from the Nb electrodes into 10⟩ triplet correlations. Subsequently, strain-induced spin-orbit coupling enables spin rotation from the triplet component 10⟩ into equal-spin components ¯11> (or ¯1−1) making the Cooper-pairs immune to the magnetic moments. This mechanism is conceptually related to the Bergeret–Volkov–Efetov theory developed for superconductor/ferromagnet/superconductor junctions. The absence of macroscopic stray field, combined with symmetry-protected momentum-dependent spin splitting, provides an ideal platform for exploring unconventional superconducting proximity effects free from the magnetic-field background associated with ferromagnets. This could give rise to an unexplored superconducting diode effect.

Improvements for AI systems

The improved AI system can model and predict long-distance Josephson supercurrent transport in altermagnet junctions exceeding conventional singlet coherence lengths by nearly two orders of magnitude, as demonstrated by observing dissipationless supercurrent across a lateral spacer distance of 150 nm in a CrSb-based Josephson junction, exceeding the conventional spin-singlet coherence length by nearly two orders of magnitude.
The system can develop predictive models for the emergence and manipulation of unconventional superconducting states, specifically simulating spin-polarized triplet Cooper pairs and finite-momentum Fulde–Ferrell–Larkin–Ovchinnikov states, which hold great potential in dissipationless superconducting electronics [3–7].
The AI can design novel spintronic devices by leveraging altermagnets to eliminate limitations of conventional ferromagnets, specifically by removing the outstanding obstacles of stray fields and complex multilayer engineering in superconducting spintronics.

Abstract

Altermagnetic materials, characterized by vanishing net magnetization and momentum-dependent spin splitting, provide a unique platform for realizing unconventional superconducting states without the detrimental stray fields. Here, we demonstrate long-distance Josephson supercurrent transport through epitaxial thin films of the strained altermagnet CrSb. We observe a dissipationless supercurrent across a lateral spacer distance of 150 nm in a CrSb-based Josephson junction, exceeding the conventional spin-singlet coherence length by nearly two orders of magnitude. This supercurrent is further accompanied by a well-defined magnetic-field-induced quantum interference pattern, providing direct evidence for genuine Josephson coupling. Our results reveal altermagnets as a promising route toward generating long-distance supercurrents without macroscopic magnetic stray fields, opening new opportunities for superconducting spintronic applications.