[논문 리뷰] Altermagnetic superconducting diode effect from non-collinear compensated magnetism in Mn$_3$Pt

Schrade, Constantin, Sujit Manna외 1명|arXiv (Cornell University)|2026. 01. 06.

Topological Materials and Phenomena인용 수 1

한 줄 요약

The paper develops a theory for the superconducting diode effect (SDE) in Mn3Pt/Nb heterostructures, showing how noncollinear altermagnetic textures with zero net magnetization induce nonreciprocal critical currents through proximity-coupled superconductivity and detailing angular and field dependencies that distinguish magnetic orders.

ABSTRACT

Altermagnets have recently emerged as a distinct class of magnetic systems that exhibit spin splitting of electronic bands while retaining zero net magnetization. This unique combination makes them a promising platform for time-reversal symmetry-breaking superconducting phenomena, although identifying concrete material platforms remains an important open challenge. Here, we develop a theory for the superconducting diode effect observed experimentally in a Mn$_3$Pt-superconductor heterostructure. Using both a symmetry analysis and model calculations on the breathing kagome lattice, we show how the altermagnetic spin textures in Mn$_3$Pt generate a spin splitting of the electronic bands that remains magnetization-free even in the presence of spin-orbit coupling and, upon taking into account the proximity coupling across the interface, produces a superconducting diode effect. We also demonstrate that the angular dependence of the critical current provides a probe of the magnetic order. We hope that our work will contribute to the understanding and further discovery of candidate materials for novel altermagnet-superconductor hybrid devices.

연구 동기 및 목표

• Motivate and define altermagnetism for noncollinear orders and zero net magnetization.
• Explain how Mn3Pt's breathing kagome lattice hosts altermagnetic spin textures.
• Analyze proximity-induced superconductivity and its role in a superconducting diode effect.

제안 방법

• Construct a tight-binding model on a breathing kagome lattice with Mn sublattices A,B,C.
• Incorporate noncollinear magnetic orders T1 and T2 and analyze spin textures with and without spin-orbit coupling.
• Compute particle-particle bubbles Pi_SC(q) and Pi_AM(q) to study superconducting instabilities and momentum dependence.
• Couple the altermagnet and conventional s-wave superconductor via interfacial tunneling T0 and derive an effective free energy F_eff(q).
• Derive expressions for proximity-induced order parameters and the supercurrent J(q) from 2e∂q F_eff(q).
• Evaluate diode efficiency η(θ) and its angular dependence for T1 and T2 phases, identifying symmetry-based zeros and experimental signatures.

Figure 1: Noncollinear altermagnetic platform for a superconducting diode effect. (a) Crystal structure of Mn 3 Pt, where Mn moments form a breathing kagome lattice in the $(111)$ plane (blue: Mn, brown: Pt). (b) Mn 3 Pt altermagnet proximitized by a conventional superconductor, giving rise to a SDE

실험 결과

연구 질문

• RQ1 How does noncollinear compensated magnetism in Mn3Pt enable a superconducting diode effect at zero net magnetization?
• RQ2 What is the role of proximity coupling to an s-wave superconductor in generating finite-momentum pairing and nonreciprocal critical currents?
• RQ3 How do T1 and T2 magnetic orders differ in their angular dependence of diode efficiency, and can this distinguish the two phases experimentally?
• RQ4 How does spin-orbit coupling modify spin textures and contribute to the SDE in Mn3Pt?
• RQ5 What are the predicted signatures of altermagnetic SDE in magnetic field and angle-dependent measurements?

주요 결과

• A superconducting diode effect arises in Mn3Pt/Nb via proximity-induced pairing even though Mn3Pt remains non-superconducting on its own.
• Pi_AM(q) is not even in q and has maxima at finite momenta related by C3 symmetry, leading to finite-momentum proximity-induced pairing in the altermagnet.
• The proximity coupling T0 induces an asymmetric, magnetism-driven contribution to the current that enhances nonreciprocity beyond the conventional superconductor term.
• The model predicts a diode efficiency up to about 4% for the T2 phase and up to about 9% for the T1 phase under their parameter set.
• The angular dependence of η(θ) differs between T1 and T2, with zeros at distinct angles, offering a spectroscopy-like probe to distinguish the two orders.
• Increasing an out-of-plane magnetic field B boosts η by suppressing the reciprocal superconducting contribution relative to the altermagnetic nonreciprocal channel.
• The results align qualitatively with experimental observations and provide signatures to identify altermagnetic superconductivity in Mn3Pt-based hybrids.

Figure 2: Normal state bands and Fermi surface spin textures for the T2 phase. (a) Band structure along $\Gamma$ – $M$ – $K$ – $\Gamma$ without spin-orbit coupling ( $\lambda=\lambda^{\prime}=0)$ , showing an altermagnetic spin splitting. (b) Same as (a) but with a staggered spin-orbit coupling on t