Quantum geometric ferromagnetism and spin-triplet superconductivity
ORAL
Abstract
Itinerant ferromagnetism has long been a central topic in condensed matter physics. Intensive investigations have been carried out to reveal the origin of itinerant ferromagnetism, and the spin-triplet superconductivity mediated by ferromagnetic fluctuation, which is the platform for topological superconductivity, has attracted much attention. However, most itinerant ferromagnets are three-dimensional systems, and candidate materials for spin-triplet superconductivity are restricted to f-electron systems. Therefore, the itinerant ferromagnetism and spin-triplet superconductivity are rare in nature, and predicting two-dimensional (2D) itinerant ferromagnets is challenging.
In this talk, we present a guiding principle for realizing itinerant ferromagnetic materials by using the concept of quantum geometry[1,2]. We propose a mechanism that quantum geometry induces ferromagnetic correlation, resulting in itinerant ferromagnetism and spin-triplet superconductivity in two dimensions. Especially, we refer to ferromagnetism arising from this mechanism as quantum geometric ferromagnetism. The key electronic structure for this phenomenon is the singular saddle point, where the saddle point appears at the band crossing point. At the singular saddle point, the divergent quantum metric induces ferromagnetic correlation, and the divergent density of states guarantees the Stoner criterion. For example, we demonstrate that the dispersive Lieb lattice and 2D t2g-orbital model exhibit the spin-triplet superconductivity mediated by quantum-geometry-induced ferromagnetic fluctuation and quantum geometric ferromagnetism, respectively. In particular, in the t2g-orbital model, quantum geometric ferromagnetism is continuously connected to rigorously proven flat-band ferromagnetism.
In this talk, we present a guiding principle for realizing itinerant ferromagnetic materials by using the concept of quantum geometry[1,2]. We propose a mechanism that quantum geometry induces ferromagnetic correlation, resulting in itinerant ferromagnetism and spin-triplet superconductivity in two dimensions. Especially, we refer to ferromagnetism arising from this mechanism as quantum geometric ferromagnetism. The key electronic structure for this phenomenon is the singular saddle point, where the saddle point appears at the band crossing point. At the singular saddle point, the divergent quantum metric induces ferromagnetic correlation, and the divergent density of states guarantees the Stoner criterion. For example, we demonstrate that the dispersive Lieb lattice and 2D t2g-orbital model exhibit the spin-triplet superconductivity mediated by quantum-geometry-induced ferromagnetic fluctuation and quantum geometric ferromagnetism, respectively. In particular, in the t2g-orbital model, quantum geometric ferromagnetism is continuously connected to rigorously proven flat-band ferromagnetism.
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Publication: [1] T. Kitamura, A. Daido, and Y. Yanase, Phys. Rev. Lett. 132, 036001 (2024).
[2] T. Kitamura, H. Nakai, A. Daido, and Y. Yanase, arXiv:2505.01089 (2025).
Presenters
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Taisei Kitamura
- RIKEN