In a landmark study recently published in Nature Physics, the team led by Qimiao Si at Rice University, in collaboration with experimental researchers at the Weizmann Institute, has achieved a remarkable visualization of the fundamental building blocks of flat band quantum materials. This discovery marks a significant milestone in the understanding of complex quantum states and paves the way for advancements in quantum technology and high-temperature superconductivity.
Flat band materials present an intriguing paradox in the study of condensed matter physics. In these substances, electrons exhibit severely restricted motion, a phenomenon driven by destructive interference patterns within their quantum states. Rather than freely moving, electrons are confined to highly localized states, creating flat electronic bands where kinetic energy is quenched. Such flat bands enhance electron correlations, leading to a host of exotic phenomena that challenge classical descriptions of metallic behavior.
More fascinating still is the topological nature of these materials. Unlike traditional materials whose properties may vary wildly under deformation, flat band quantum materials maintain robust characteristics even as they undergo continuous bending or stretching, as long as the symmetries defining their structure remain preserved. This resilience is underpinned by topological invariants—mathematical quantities that remain constant despite continuous transformations—which govern the electronic states and their global configuration.
Graduate student Mounica Mahankali, a co-first author of the study, describes how the quantum states in these materials acquire what is known as a winding number. This number encapsulates the notion that as one navigates through the intricate space of electron states and returns to the original point, the state of the system undergoes a global twist—a signature characteristic of topological order. The presence of such topological winding numbers hints at profound underlying physics dictating the behavior of electrons, especially when electron-electron interactions are strong.
Qimiao Si’s prior theoretical work, published in Science Advances, opened new avenues to explore how topology intertwines with electronic correlations, particularly near the elusive quantum critical point. This critical point represents a phase transition that occurs at zero temperature due to quantum fluctuations—a juncture where the electronic system delicately balances between distinct ground states. Si’s theory postulated that compact molecular orbitals could serve as the fundamental mediators of the flat bands within these materials, effectively acting as localized wavefunctions from which the quantum critical behavior emerges.
To visualize this complex scenario, Si employed an analogy likening the quantum system to a highway with two lanes: one lane experiencing heavy congestion symbolizing the localized, ordered electronic states, and another representing fast-moving, liquid-like itinerant states. Just as cars move between lanes to navigate traffic conditions, electrons dynamically redistribute to balance localization and mobility. At the quantum critical point, this delicate balance reaches a tipping point, allowing the system to fluctuate between these extremes. Compact molecular orbitals correspond to the jammed lane, whose characterization can reveal the nature of the fast-moving itinerant states.
Despite the elegance of this theoretical framework, direct experimental verification remained a critical challenge. This hurdle was overcome through a fortuitous collaboration between Si and Haim Beidenkopf, an experimental physicist at the Weizmann Institute with expertise in atomic-resolution spectroscopic imaging of quantum materials. Their shared interests converged during a joint visit at the Kavli Institute for Theoretical Physics, sparking experimental investigations directly informed by theoretical predictions.
The material chosen for this groundbreaking experiment was Ni3In, a highly correlated metal known for its unusually agitated electron dynamics. Intriguingly, Ni3In is a d-orbital kagome metal, a lattice characterized by a distinctive geometry that promotes flat band formation and complex electron interactions. Its potential practical significance lies in its prospective relation to mechanisms of high-temperature superconductivity, where electron correlation effects are central.
Beidenkopf’s team utilized an atomic resolution spectrometer to map the spatial distribution of current flow within Ni3In. By attaining atomic-scale insight, they could discern how electrons traverse the kagome lattice and how their movement is modulated by the presence of flat bands. The experimental data revealed spatial profiles precisely matching those predicted by the existence of compact molecular orbitals, providing compelling evidence for these orbitals’ role in shaping the quantum critical state.
Integrating Si’s theoretical insights with the experimental measurements allowed the team to identify the kagome lattice’s intrinsic topology as the root cause of the observed quantum criticality. This multidisciplinary synergy demonstrated that the compact molecular orbitals underlie the unusual metallic state of Ni3In, effectively bridging theory and experiment in a domain often hampered by the subtlety of quantum phenomena.
This collaboration and its results fundamentally enrich the understanding of strange metallicity—a non-Fermi liquid behavior observed when metals defy classical transport theory—by tying it to the topology of the underlying electronic states. Such strange metallic states are linked to unconventional superconductivity and quantum criticality, making the findings pivotal for designing materials with tailored quantum properties.
Beyond academic curiosity, this research offers a promising pathway toward harnessing topological quantum materials for future quantum devices. The precise control over electron correlations and the ability to visualize their fundamental agents open opportunities for developing technologies that leverage quantum criticality and flat band physics in robust, tunable platforms.
The pioneering work at Rice University was supported by the U.S. Department of Energy’s Basic Energy Sciences program, with complementary funding for the Weizmann team and collaborators arising from a suite of prestigious sources including the BSF-NSF-Materials grant, the Gordon and Betty Moore Foundation, the U.S. Army Research Office, and others. This reflects the high interdisciplinary value and strategic importance of unraveling fundamental quantum behaviors with practical implications.
As the frontiers of quantum materials science expand, such studies underscore the importance of bridging theoretical constructs with cutting-edge experimental techniques. The joint effort between Rice and the Weizmann Institute exemplifies how collaborative cross-pollination can foster breakthroughs that redefine understanding and control of quantum matter—a critical step toward realizing new quantum technologies.
In summary, the visualization of compact molecular orbitals in Ni3In heralds a new chapter in the study of flat band materials, revealing the intricate dance of electrons governed by topology and strong correlations. The insights gleaned deepen comprehension of quantum criticality and strange metallic states, promising to accelerate the quest for novel superconductors and quantum devices optimized at the atomic scale.
Subject of Research: Not applicable
Article Title: Origin of strange metallicity in a d-orbital kagome metal
News Publication Date: 17-Mar-2026
Web References:
10.1038/s41567-026-03216-4
References:
Si, Qimiao et al. “Origin of strange metallicity in a d-orbital kagome metal.” Nature Physics, 2026.
Image Credits: —
Keywords
Quantum mechanics, Band structures
