Theory of Superconductivity in LaRu$_3$Si$_2$ and Predictions of New Kagome Flat Band Superconductors
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| Natura: | Preprint |
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2025
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| author | Deng, Junze Jiang, Yi Cerqueira, Tiago F. T. Hu, Haoyu Lamponen, Eeli O. Călugăru, Dumitru Pi, Hanqi Wang, Zhijun Vergniory, Maia G. Morosan, Emilia Neupert, Titus Blanco-Canosa, S. Felser, Claudia Haule, Kristjan Marques, Miguel A. L. Törmä, Päivi Bernevig, B. Andrei |
| author_facet | Deng, Junze Jiang, Yi Cerqueira, Tiago F. T. Hu, Haoyu Lamponen, Eeli O. Călugăru, Dumitru Pi, Hanqi Wang, Zhijun Vergniory, Maia G. Morosan, Emilia Neupert, Titus Blanco-Canosa, S. Felser, Claudia Haule, Kristjan Marques, Miguel A. L. Törmä, Päivi Bernevig, B. Andrei |
| contents | We present a comprehensive investigation of the flat-band kagome superconductor LaRu$_3$Si$_2$, which has recently been reported to host charge density wave (CDW) order above room temperature ($T_{CDW} \simeq 400$ K). The stable crystal structure above the CDW transition is identified via soft phonon condensation and confirmed to be harmonically stable through ab initio calculations, consistent with recent X-ray diffraction refinements. The electron-phonon coupling (EPC) in LaRu$_3$Si$_2$ is found to be mode-selective, primarily driven by strong interactions between Ru-$B_{3u}$ phonons (local $x$-direction, pointing toward the hexagon center) and Ru-$A_g$ electrons (local $d_{x^2-y^2}$ orbital) within the kagome lattice. Using a spring-ball model, we identify this mode-selective EPC as a universal feature of kagome materials. Employing the newly developed Gaussian approximation of the hopping parameters, we derive an analytical expression for the EPC and demonstrate that superconductivity in LaRu$_3$Si$_2$ is mostly driven by the coupling between the kagome $B_{3u}$ phonons and the $A_g$ electrons. The impact of doping is also investigated, revealing that light hole doping (approximately one hole per unit cell) significantly enhances the superconducting critical temperature $T_c$ by 50%, whereas heavy doping induces structural instability and ferromagnetism. Furthermore, high-throughput screening identifies 3063 stable 1:3:2 kagome materials, of which 428 are predicted to exhibit superconductivity with $T_c > 1$ K, and the highest $T_c$ reaching 15 K. These findings establish LaRu$_3$Si$_2$ and related materials as promising platforms for exploring the interplay among kagome flat bands, EPC, and superconductivity. Additionally, they may offer valuable insights into potential limitations on the $T_c$ of flat-band superconductivity in real materials. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2503_20867 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Theory of Superconductivity in LaRu$_3$Si$_2$ and Predictions of New Kagome Flat Band Superconductors Deng, Junze Jiang, Yi Cerqueira, Tiago F. T. Hu, Haoyu Lamponen, Eeli O. Călugăru, Dumitru Pi, Hanqi Wang, Zhijun Vergniory, Maia G. Morosan, Emilia Neupert, Titus Blanco-Canosa, S. Felser, Claudia Haule, Kristjan Marques, Miguel A. L. Törmä, Päivi Bernevig, B. Andrei Superconductivity We present a comprehensive investigation of the flat-band kagome superconductor LaRu$_3$Si$_2$, which has recently been reported to host charge density wave (CDW) order above room temperature ($T_{CDW} \simeq 400$ K). The stable crystal structure above the CDW transition is identified via soft phonon condensation and confirmed to be harmonically stable through ab initio calculations, consistent with recent X-ray diffraction refinements. The electron-phonon coupling (EPC) in LaRu$_3$Si$_2$ is found to be mode-selective, primarily driven by strong interactions between Ru-$B_{3u}$ phonons (local $x$-direction, pointing toward the hexagon center) and Ru-$A_g$ electrons (local $d_{x^2-y^2}$ orbital) within the kagome lattice. Using a spring-ball model, we identify this mode-selective EPC as a universal feature of kagome materials. Employing the newly developed Gaussian approximation of the hopping parameters, we derive an analytical expression for the EPC and demonstrate that superconductivity in LaRu$_3$Si$_2$ is mostly driven by the coupling between the kagome $B_{3u}$ phonons and the $A_g$ electrons. The impact of doping is also investigated, revealing that light hole doping (approximately one hole per unit cell) significantly enhances the superconducting critical temperature $T_c$ by 50%, whereas heavy doping induces structural instability and ferromagnetism. Furthermore, high-throughput screening identifies 3063 stable 1:3:2 kagome materials, of which 428 are predicted to exhibit superconductivity with $T_c > 1$ K, and the highest $T_c$ reaching 15 K. These findings establish LaRu$_3$Si$_2$ and related materials as promising platforms for exploring the interplay among kagome flat bands, EPC, and superconductivity. Additionally, they may offer valuable insights into potential limitations on the $T_c$ of flat-band superconductivity in real materials. |
| title | Theory of Superconductivity in LaRu$_3$Si$_2$ and Predictions of New Kagome Flat Band Superconductors |
| topic | Superconductivity |
| url | https://arxiv.org/abs/2503.20867 |