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

Selvamanickam’s impressive journey in the domain of superconducting materials spans several decades. He has successfully merged scientific research with industrial applications, effectively bringing innovative ideas from the laboratory to commercial viability. His work primarily focuses on high-temperature superconducting wires, which play a crucial role in enhancing electric power applications. As the director of the Advanced Manufacturing Institute at the Cullen College of Engineering, he aims to accelerate the domestic production of superconductors while fostering partnerships with both federal agencies and industry leaders.

The essence of his research lies in the unique properties of high-temperature superconductors, which can conduct electricity with zero resistance at relatively higher temperatures compared to conventional superconductors. This characteristic allows the development of energy systems that are not only more efficient but also capable of handling the increasing demand for power in modern societies. By innovating in this field, Selvamanickam has helped enhance energy resilience and facilitate the modernization of electrical grids, ensuring they can support the growing energy needs across various sectors.

Profoundly aware of the significance of his contributions, Selvamanickam expresses his gratitude toward his students, colleagues, and industry partners. His collaborative approach reflects a broader trend in engineering, where interdisciplinary teamwork is vital for advancing knowledge and creating impactful technologies. He recognizes that the progress made in superconductivity is not merely the result of individual efforts; rather, it is a collective mission to advance technologies that have the potential to redefine energy infrastructure and apply in various domains, including transportation and medical technologies.

His election to the NAE puts him among the ranks of 130 U.S. members and 28 international members, signifying the global impact of his work. As the 29th NAE member from the University of Houston, Selvamanickam’s achievement proliferates the institution’s reputation as a leader in engineering research and education, especially in the burgeoning field of superconductivity. His efforts have not only elevated the university’s standing but also created opportunities for students to engage with pioneering work that shapes the future of energy technology.

In addition to the accolades, Selvamanickam has secured significant federal funding, specifically an $8 million grant aimed at advancing research related to superconducting magnets for compact fusion reactors. These initiatives are crucial in driving forward the development of next-generation energy systems that promise to be less dependent on fossil fuels and more efficient in harnessing energy from renewable sources. The integration of superconducting technologies into fusion reactors could ultimately revolutionize clean energy generation, bringing us closer to sustainable energy solutions.

The growing emphasis on superconductivity can be attributed to its potential applications in various energy sectors, including the development of maglev trains, efficient energy storage systems, and enhanced medical imaging technologies such as MRI. Each application demonstrates how superconductors can transform everyday systems by improving efficiency, reducing energy loss, and enabling new capabilities that were previously deemed impossible. As such, research into superconducting materials is not just an academic exercise but a pathway to real-world innovations that can benefit society as a whole.

Selvamanickam’s work aligns with the current trends in energy technologies that prioritize both efficiency and sustainability. Engineers and researchers are increasingly challenged to devise solutions that address energy demands while minimizing environmental footprints. By pushing the envelope of what is achievable with superconductive materials, Selvamanickam plays a critical role in guiding future research directions and cultivating a new generation of engineers equipped to tackle these pressing challenges.

The recognition bestowed upon Selvamanickam from the National Academy of Engineering exemplifies how impactful engineering can drive societal change. It is a testament to the importance of innovation in achieving economic development and improving quality of life. The contributions he has made not only elevate his career but also inspire others in academia and industry to pursue excellence in their fields. This interplay between research and practice is vital in creating an ecosystem where innovative ideas can flourish, leading to groundbreaking advancements that resonate on a global scale.

This milestone is also an acknowledgment of the comprehensive educational initiatives at the University of Houston, where students are immersed in an environment that encourages practical learning through collaboration with established professionals like Selvamanickam. Such opportunities at the university bridge the gap between theoretical knowledge and real-world applications, preparing students for fulfilling careers as they step into a rapidly evolving job market that increasingly values expertise in science and engineering.

Selvamanickam’s induction into the National Academy of Engineering will culminate in an official ceremony during the Academy’s Annual Meeting this fall. It is expected to draw attention not only to his achievements but also to the broader implications of his work for the engineering community at large. As leaders in the field gather to celebrate such milestones, it reinforces the mission of organizations like the NAE to recognize and promote the advancement of engineering as a vital pillar of modern society.

Encouragingly, his work will undoubtedly serve as a reference point for ongoing research endeavors in superconductivity and related fields. The advancements made by Selvamanickam open up new avenues of inquiry and encourage a culture of innovation that is necessary for driving technological progress in the face of global energy challenges. It is through such dedicated efforts that the bridge can be built between aspirational research and practical, life-altering applications in energy systems and beyond.

Venturing further into the implications of superconducting technologies, one cannot overlook the broader societal impacts. The transition towards advanced superconducting solutions can enhance industrial capabilities and transform energy generation and distribution methods, propelling society toward a future characterized by sustainable and efficient energy practices. Professor Selvamanickam embodies the archetypal engineer whose contributions resonate beyond borders and redefine how we integrate technology into our lives.

This momentous achievement heralds a future where the coupling of scientific research and engineering proficiency leads to meaningful advancements in energy technologies. The journey that Selvamanickam has embarked upon is not solely an individual path but rather a beacon for aspiring engineers globally to harness the potential of science and apply it for the greater good. As more researchers and students engage in this impactful field, the landscape of engineering is poised for transformative changes that will redefine how we understand and utilize energy moving forward.

Subject of Research: High-temperature superconducting technologies and their industrial applications.
Article Title: University of Houston’s Venkat Selvamanickam Elected to National Academy of Engineering
News Publication Date: October 2023
Web References: University of Houston Press Release
References: Academic publications from Venkat Selvamanickam and National Academy of Engineering records.
Image Credits: Credit: University of Houston

Keywords

Superconductivity, electric power applications, engineering innovation, high-temperature superconductors, advanced manufacturing, energy resilience, superconducting magnet research, compact fusion reactors, electrical grid modernization, interdisciplinary collaboration, energy technologies, academic leadership.

Two-dimensional materials, typified by graphene and transition metal dichalcogenides, have revolutionized our understanding of condensed matter, providing platforms for exploring quantum confinement, topological states, and novel electronic phases. However, the family of transition metal oxides—renowned for their complex and strongly correlated electronic interactions such as high-temperature superconductivity, magnetism, and Mott insulating behavior—has remained largely inaccessible in two-dimensional forms. This is primarily due to the robust ionic bonding within TMOs, which precludes the formation of easily exfoliable van der Waals layers characteristic of 2D materials.

This barrier was overcome through a masterful chemical strategy executed by a research team led by Assistant Professor Takuto Soma at the Institute of Science Tokyo (Science Tokyo). By selectively extracting lithium ions from the layered oxide parent compound LiNbO₂ via high-temperature oxidative deintercalation, the team successfully transformed a bulk three-dimensional oxide into a layered 2D vdW material with strong electronic correlations. The resulting 2H-NbO₂ possesses a hexagonal honeycomb lattice structure stacked in two repeating layers, an architecture reminiscent of classic vdW materials yet embedded with the rich electron-electron interactions characteristic of strongly correlated TMOs.

The electronic structure of 2H-NbO₂ has been meticulously analyzed, revealing a half-filled band dominated by Nb 4d orbitals. This configuration induces pronounced Coulomb repulsion among electrons, effectively driving the system into a Mott insulating state despite the presence of partially filled metallic bands. Such strongly correlated electronic behavior is foundational to unconventional phenomena like metal-insulator transitions and superconductivity, making 2H-NbO₂ an ideal testbed for investigating these emergent effects in a truly two-dimensional setting.

Notably, partial deintercalation of lithium ions in 2H-NbO₂ results in a rich phase diagram where metal-insulator transitions coexist with the onset of superconductivity and non-Fermi liquid behavior. These phenomena mirror critical aspects observed in high-temperature copper oxide superconductors and the emergent electronic phases engineered within Moiré superlattices formed by twisted 2D materials. The ability to controllably tune these phases in a chemically synthesized vdW oxide signifies a paradigm shift in the design and exploration of quantum materials.

At its core, this research bridges two traditionally separate domains: the physics of strongly correlated electron systems embodied by transition metal oxides, and the structural flexibility and manipulation offered by 2D materials. Dr. Soma emphasizes that this fusion “unlocks a new class of quantum materials that harmonize strong electronic correlations with van der Waals flexibility,” laying the groundwork for novel device architectures with unprecedented functionalities.

The implications of synthesizing 2H-NbO₂ extend beyond fundamental science; they herald exciting technological prospects. For instance, devices based on correlated oxides exhibit unique responses to external stimuli like electric and magnetic fields, enabling dynamic control over conductivity, magnetism, and superconductivity. Such tunability in a 2D platform is ideal for ultra-compact, energy-efficient electronics and next-generation quantum information technologies, wherein control at the atomic scale is paramount.

Synthesizing 2H-NbO₂ involved an intricate process starting from epitaxial thin films of LiNbO₂. The researchers leveraged a high-temperature oxidative environment to selectively remove lithium ions without disturbing the underlying niobium-oxygen framework. This selective lithium extraction gave rise to the 2H polytype structure, maintaining atomic-scale order and producing a stable 2D van der Waals lattice. This methodology not only introduces a new material family but also sets a precedent for chemically engineering vdW oxides through ion manipulation.

Detailed spectroscopic and transport measurements confirmed the strongly correlated nature of 2H-NbO₂. The material transitions from a Mott insulator to a metallic and superconducting state upon precise control of lithium content, highlighting the delicate balance between electron localization and itinerancy. This tunability is a hallmark of correlated electron materials and reveals a fertile playground to study intertwined quantum phases in low dimensions.

From a theoretical perspective, 2H-NbO₂ presents opportunities to unravel unresolved questions about electron correlations in reduced dimensionality. The interplay between lattice geometry, electron interactions, and vdW stacking conditions could elucidate mechanisms governing high-temperature superconductivity and exotic magnetic orderings. Such insights will inform models applicable across a swath of quantum materials where electronic correlations compete with lattice effects.

The collaborative effort involved leading experts from the Institute of Science Tokyo, along with contributions from Tohoku University, exemplifying how cross-institutional partnerships accelerate discovery. The team’s findings, published in the prestigious journal ACS Nano, have already inspired a surge of interest in chemically synthesized van der Waals oxides, with researchers worldwide aiming to replicate and extend this work to other transition metal oxide systems.

As the science community continues to explore the boundaries of 2D materials, the synthesis of 2H-NbO₂ signifies a momentous step forward. By harnessing the combined advantages of strong electron correlations and van der Waals assembly, this new material class bridges a critical gap, promising a future where quantum electronic devices transcend current limitations. The versatility and tunability of 2H-NbO₂ are poised to energize both basic research and applied development, potentially ushering in a new era of quantum materials engineering.

Moving forward, continued studies will focus on refining control over lithium deintercalation, exploring the detailed phase behavior under various external parameters, and integrating 2H-NbO₂ into device architectures. This research not only enriches our fundamental understanding but also accelerates progress toward practical technologies that leverage quantum phenomena at the atomic scale.

By synthesizing 2H-NbO₂, researchers have effectively realized a dream long held in materials science: combining the best of both worlds—strong electronic correlations typical of 3D oxides and the unparalleled structural tunability of 2D materials. This innovation not only redefines the landscape of quantum materials but also sets the stage for future discoveries that can transform electronics, energy applications, and quantum information science.

Subject of Research: Two-dimensional van der Waals oxides with strongly correlated electronic properties

Article Title: Strongly Correlated van der Waals Oxide: 2H‑NbO2

News Publication Date: 29 July 2025

Web References:
https://doi.org/10.1021/acsnano.5c05513

Image Credits: Institute of Science Tokyo (Science Tokyo)

Keywords

Two dimensional materials, Electronic devices, Electrical engineering, Technology, Electronics, Applied sciences and engineering, Materials science, Quantum chemistry

At the heart of this work lies the canonical t–J model—a theoretical framework capturing the competition between the kinetic energy of hole dopants, characterized by the tunneling amplitude t, and the AFM spin exchange interaction J. Traditionally, numerical simulations of this model have been constrained by formidable computational challenges, particularly in regimes of high particle density and complex geometry. The direct quantum simulation of t–J physics within a controllable experimental setup, therefore, represents a milestone in pushing the boundaries of quantum simulation towards solving practically relevant condensed matter problems.

The research team leveraged a Rydberg tweezer platform, manipulating arrays of atoms excited to high principal quantum number Rydberg states, to construct and control a bosonic t–J–V model with tunable parameters. By encoding spin states and vacant hole sites into coherent dynamics among three distinct Rydberg levels, they realized a highly flexible quantum simulator that accesses parameter regimes previously out of reach. Crucial to this approach was the incorporation of next-nearest-neighbor (NNN) tunneling terms, labeled as t′, which introduce subtle interference effects in hole motion and profoundly influence pairing dynamics and phase separation phenomena.

One of the pivotal observations from the experiments was the spontaneous dynamical phase separation between hole-rich and spin-rich domains when the tunneling amplitude was much smaller than the spin interaction strength (|t/J| ≪ 1). Such phase separation reflects a delicate balance where kinetic restrictions encourage holes to cluster, thereby minimizing the frustration in the underlying antiferromagnetic order. This behavior echoes theoretical predictions about phase separation phenomena in doped Mott insulators but had remained elusive to direct observation in cold atom setups until now.

Beyond this, the experiments revealed compelling evidence for the formation of repulsively bound pairs of hole dopants. These pairs arise not from the conventional attraction but through an emergent binding mechanism mediated by the spin background and the interference between NNN tunneling paths and effective pair tunneling processes. This novel type of pairing, sensitive to the sign and magnitude of the nearest-neighbor hopping parameter t, distinguishes “light” and “heavy” pairs that exhibit markedly different mobility and coherence properties.

Using single-site addressability inherent to the Rydberg tweezer platform, the researchers were also able to probe the dynamics of individual holes embedded in two-dimensional square lattice magnets with both antiferromagnetic and ferromagnetic correlations. This capability to track single dopants in a complex, interacting spin environment provides an unparalleled window into the microscopic mechanisms underpinning charge and spin transport in correlated quantum materials. It represents a crucial step towards unraveling the fate of mobile carriers in strongly correlated backgrounds in real time.

Importantly, the model implemented in this experiment extends the scope of quantum simulation beyond conventional spin-1/2 frameworks to encompass spin-1 degrees of freedom as well as generalized t–J and t–J–V Hamiltonians. This versatility opens doors to studying a rich tapestry of quantum magnetism, charge dynamics, and unconventional pairing phenomena with tailored interactions. The bosonic nature of the holes and the fine control over near- and next-nearest neighbor interactions provide an experimental playground to explore exotic phases, including potential analogs of superconductivity and stripe order, within a fully coherent quantum environment.

The integration of coherent control, long coherence times, and flexible lattice geometries underscores the transformative potential of Rydberg tweezer arrays in simulating quantum many-body models that have remained largely theoretical. Their platform deftly surmounts the difficulties of competing energy scales and frustration effects, allowing for direct exploration of regimes where the kinetic and magnetic energy scales are carefully balanced. This is crucial for understanding how quantum phases compete, coexist, or evolve with doping in models relevant to high-Tc superconductivity and other correlated phenomena.

Moreover, the study’s detailed characterization of the interplay between NNN tunneling processes and perturbative pair tunneling illuminates the nuanced mechanisms by which complex hopping pathways affect microscopic pairing and mass renormalization of hole pairs. These insights shed light on longstanding conjectures about the role of second-neighbor hopping in stabilizing or suppressing superconducting correlations in the Hubbard and t–J models, providing fresh experimental benchmarks against which theoretical predictions can be tested.

By harnessing the unique capabilities of Rydberg-mediated interactions and site-resolved control, the work sets a new standard for quantum emulation of correlated electron systems. It bridges the gap between abstract theoretical models and tangible experimental realizations, offering a robust testbed for future studies to systematically investigate doping-dependent phase transitions, emergent quasiparticles, and the dynamical formation of correlations in two-dimensional lattice systems. This promises not only to deepen fundamental understanding but also to inspire novel quantum technologies leveraging strongly correlated quantum matter.

Looking forward, this pioneering realization of a doped quantum antiferromagnet is poised to invigorate experimental and theoretical inquiries into the rich physics of doped Mott insulators. As quantum simulation platforms continue to advance, they hold the promise of unraveling mysteries surrounding unconventional superconductivity, non-Fermi liquid behavior, and intertwined orders—all pivotal phenomena in modern condensed matter physics. The ability to engineer and probe such systems with unprecedented control may ultimately guide the rational design of materials with tailored electronic properties.

In conclusion, the innovative use of Rydberg tweezer arrays to emulate a bosonic t–J–V model with next-nearest-neighbor hopping marks a major leap forward in quantum simulation of strongly correlated systems. The experimental observation of phase separation, repulsively bound hole pairs, and the tunable dynamics of dopants in controlled spin environments is a testament to the power and precision of this approach. By extending the simulation paradigm beyond spin-1/2 models and into broader classes of quantum magnetism and charge dynamics, this work opens exciting new avenues for exploring the complex quantum many-body phenomena that underpin some of the most intriguing states of matter.

The findings not only provide immediate insights into longstanding theoretical puzzles but also establish a versatile platform capable of accessing novel, exotic quantum phases under experimentally tunable conditions. As the frontier of quantum simulation continues to expand, studies like this exemplify the critical synergy between advanced experimental techniques and theoretical frameworks, driving the field closer to unraveling the quantum secrets hidden within doped antiferromagnets and beyond.

Subject of Research: Quantum simulation of doped quantum antiferromagnets and strongly correlated electron systems using Rydberg tweezer arrays.

Article Title: Realization of a doped quantum antiferromagnet in a Rydberg tweezer array.

Article References:
Qiao, M., Emperauger, G., Chen, C. et al. Realization of a doped quantum antiferromagnet in a Rydberg tweezer array. Nature (2025). https://doi.org/10.1038/s41586-025-09377-1

Image Credits: AI Generated