A research team has provided the first experimental proof that flat electronic bands in a kagome superconductor are active and directly shape electronic and magnetic behaviors.
Researchers from Rice University, working with international partners, have found the first clear evidence of active flat electronic bands within a kagome superconductor. The discovery marks an important step toward creating new strategies for designing quantum materials, including superconductors, topological insulators, and spin-based electronics, which could play a central role in advancing future electronics and computing.
The findings, published on August 14 in Nature Communications, focus on the chromium-based kagome metal CsCr₃Sb₅, a material that becomes superconducting when placed under pressure.
Kagome metals are defined by their unique two-dimensional lattice of corner-sharing triangles. Recent theories have suggested that these structures can host compact molecular orbitals, or standing-wave patterns of electrons, which may enable unconventional superconductivity and unusual magnetic states driven by electron correlation effects.
In most known materials, such flat bands are positioned too far from the relevant energy levels to influence behavior. In CsCr₃Sb₅, however, they play an active role and directly shape the properties of the material.
Pengcheng Dai, Ming Yi, and Qimiao Si of Rice’s Department of Physics and Astronomy and Smalley-Curl Institute, along with Di-Jing Huang of Taiwan’s National Synchrotron Radiation Research Center, led the study.
“Our results confirm a surprising theoretical prediction and establish a pathway for engineering exotic superconductivity through chemical and structural control,” said Dai, the Sam and Helen Worden Professor of Physics and Astronomy.
The finding provides experimental proof for ideas that had only existed in theoretical models. It also shows how the intricate geometry of kagome lattices can be used as a design tool for controlling the behavior of electrons in solids.
“By identifying active flat bands, we’ve demonstrated a direct connection between lattice geometry and emergent quantum states,” said Yi, an associate professor of physics and astronomy.
Experimental Techniques and Findings
The research team employed two advanced synchrotron techniques alongside theoretical modeling to investigate the presence of active standing-wave electron modes. They used angle-resolved photoemission spectroscopy (ARPES) to map electrons emitted under synchrotron light, revealing distinct signatures associated with compact molecular orbitals. Resonant inelastic X-ray scattering (RIXS) measured magnetic excitations linked to these electronic modes.
“The ARPES and RIXS results of our collaborative team give a consistent picture that flat bands here are not passive spectators but active participants in shaping the magnetic and electronic landscape,” said Si, the Harry C. and Olga K. Wiess Professor of Physics and Astronomy, “This is amazing to see given that, until now, we were only able to see such features in abstract theoretical models.”
Theoretical support was provided by analyzing the effect of strong correlations starting from a custom-built electronic lattice model, which replicated the observed features and guided the interpretation of results. Fang Xie, a Rice Academy Junior Fellow and co-first author, led that portion of the study.
Obtaining such precise data required unusually large and pure crystals of CsCr₃Sb₅, synthesized using a refined method that produced samples 100 times larger than previous efforts, said Zehao Wang, a Rice graduate student and co-first author.
The work underscores the potential of interdisciplinary research across fields of study, said Yucheng Guo, a Rice graduate student and co-first author who led the ARPES work.
“This work was possible due to the collaboration that consisted of materials design, synthesis, electron and magnetic spectroscopy characterization, and theory,” Guo said.
Reference: “Spin excitations and flat electronic bands in a Cr-based kagome superconductor” by Zehao Wang, Yucheng Guo, Hsiao-Yu Huang, Fang Xie, Yuefei Huang, Bin Gao, Ji Seop Oh, Han Wu, Jun Okamoto, Ganesha Channagowdra, Chien-Te Chen, Feng Ye, Xingye Lu, Zhaoyu Liu, Zheng Ren, Yuan Fang, Yiming Wang, Ananya Biswas, Yichen Zhang, Ziqin Yue, Cheng Hu, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Makoto Hashimoto, Donghui Lu, Junichiro Kono, Jiun-Haw Chu, Boris I. Yakobson, Robert J. Birgeneau, Guang-Han Cao, Atsushi Fujimori, Di-Jing Huang, Qimiao Si, Ming Yi and Pengcheng Dai, 14 August 2025, Nature Communications.
DOI: 10.1038/s41467-025-62298-5
Funding: U.S. Department of Energy, Welch Foundation, Gordon and Betty Moore Foundation, Air Force Office of Scientific Research, U.S. National Science Foundation
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3 Comments
The cited paper deepens the mystery of the connection between flat bands, flat band splitting and emergent ordered phases. Tuning these engineered materials to a predictable ordered phase remains challenging because of the lack of understanding of the aforementioned processes. The authors also repeat a worn-out explanation that strange metallicity in these materials (non-Fermi liquid transport) is in proximity to a mysterious quantum critical point, or exhibit “metallic quantum criticality,” when the reality is that such transport results from disorder and dimensionality of the material.
Researchers confirmed active flat bands in a kagome superconductor, opening new possibilities for designing quantum materials and future electronic technologies.
VERY GOOD.
Please ask researchers to think deeply:
How are the active flat bands formed?
With advancements in experimental techniques and theoretical frameworks, Topological Vortex Theory (TVT) is expected to become an important paradigm for explaining complex physical phenomena by around 2030, bringing revolutionary breakthroughs to next-generation information technologies and energy materials.
As a rapidly developing interdisciplinary field, future research in TVT will exhibit three major trends: precision in fundamental theories, intelligent material design, and diversified technological applications.
If researchers are interested, please browse https://zhuanlan.zhihu.com/p/1942195688579510790 (If the link is available).
Ask the researchers again:
1. What aer the quantum?
2. Where does quantum come from?
3. Where does the singularity come from?
4. Where does the energy of the singularity explosion come from?
5. Isn’t space everywhere?
6. Where do things in space come from?
7. Why does physics today ignore the ubiquity of space and instead search for imaginary God particles everywhere?
8. Isn’t space a physical entity?
9.As a physical entity, what physical properties should space possess?
10. If the space does not have physical entity properties, please inform the public where the physics experiment was conducted?
Some so-called peer-reviewed publications in physics today have misled and fooled an entire generation with their own filth and ugliness.