Cold Atoms Connect Single-Layer Models to Kondo Lattice Physics, Revealing RKKY Interactions
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The intricate behaviour of interacting electrons gives rise to fascinating phenomena, and researchers now propose a novel approach to explore the Kondo effect, a key process in understanding correlated electron systems. Hannah Lange, Eugene Demler, Jan von Delft, and colleagues at Ludwig-Maximilians-Universität München and ETH Zurich demonstrate how ultracold atoms can simulate a unique system connecting the Kondo lattice model with the behaviour of high-temperature superconductors. Their work predicts that experimentally achievable conditions will reveal the formation of ‘Kondo clouds’ and the interplay between electron interactions, offering a pathway to visualise the Doniach phase diagram. Significantly, this research establishes a direct link between the physics of heavy-fermion materials and cuprate superconductivity, opening up exciting possibilities for experimental investigation using existing quantum simulation platforms. The Kondo effect, a central concept in many-body physics, arises from the interaction between localized magnetic moments and conducting electrons, leading to the formation of correlated quantum states. This work proposes utilizing a mixed-dimensional (mixD) bilayer Hubbard model as a platform to investigate Kondo lattice physics with current ultracold atom experiments, predicting that key signatures of the Kondo effect, including the development of Kondo clouds around individual impurities and the competition between singlet pairing and long-range interactions, will be observable at experimentally accessible temperatures. This approach offers a new route to explore strongly correlated electron systems and understand the fundamental physics governing the Kondo effect in a controlled laboratory setting, providing a unique environment to tune interactions and observe emergent phenomena relevant to condensed matter physics.
Bilayer Hubbard Model for Kondo Physics This research details a sophisticated theoretical model, the mixD bilayer Hubbard model, designed to simulate Kondo physics and potentially reveal exotic quantum phenomena. The model mimics a quantum dot coupled to a two-dimensional electron gas, allowing scientists to investigate a range of quantum behaviors. Simulations rely on the Time-Dependent Variational Principle, implemented using the Syten tensor network library, to accurately track the system’s evolution over time, with particle and spin conservation explicitly enforced to enhance accuracy. Analysis focuses on the local density of states and the impurity spectral function, providing insights into the electronic structure and characterizing the Kondo effect. The research demonstrates how the complex bilayer model can be simplified under specific conditions, mapping onto more tractable single-layer models. Under strong interactions, the model simplifies to the single-layer t-J model, a standard model for studying high-temperature superconductivity, while with weaker interactions, it maps to the Fermi-Hubbard model, a more general model encompassing both hopping and interactions. This flexibility, relevance to real materials, and suitability for studying quantum phase transitions make the mixD model a powerful tool for investigating strongly correlated systems. Kondo Physics in MixD Bilayer Hubbard Model This work demonstrates a novel pathway to explore strongly correlated quantum systems using a mixed-dimensional (mixD) bilayer Hubbard model, designed for implementation with current ultracold atom experiments. Scientists predict that key features of the Kondo effect, including the formation of Kondo clouds around impurities and the competition between singlet formation and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, are observable at experimentally feasible temperatures. The research establishes a direct connection between the Doniach phase diagram of the Kondo lattice model, relevant to heavy-fermion materials, and the phase diagram of cuprate superconductors, allowing continuous tuning between these regimes by adjusting the interlayer Kondo coupling.
The team shows that with strong interlayer coupling, the system maps exactly onto the single-layer Zhang-Rice type t-J model, a crucial component in understanding the behavior of cuprate superconductors, replicating the three-band model of Cu-O layers found in these materials with the formation of singlets behaving as mobile, fermionic dopants. Measurements confirm that the doping level, controlled by the density of conduction layer fermions, directly corresponds to the density of these dopants, providing direct experimental access to the properties of individual charge carriers. Conversely, for smaller coupling, the research reveals the competition between Kondo singlet formation and RKKY interactions, giving rise to a Doniach-type phase diagram, predicting that a continuous connection between the single-layer models and the Kondo lattice model can be experimentally observed.
Kondo Physics Unifies Superconductor Insights This research demonstrates a novel platform for exploring fundamental physics related to strongly correlated electron systems, specifically utilizing a mixed-dimensional bilayer Hubbard geometry with ultracold atoms. Scientists successfully predict the observation of key features of the Kondo effect, including the formation of Kondo clouds around impurities and the competition between singlet formation and long-range interactions, within experimentally achievable temperature ranges. Importantly, the team reveals a direct connection between the physics governing heavy-fermion materials and that of high-temperature cuprate superconductors, offering a pathway to study these seemingly disparate phenomena within a unified experimental setup. The findings establish a tunable system where researchers can effectively bridge the gap between the Doniach phase diagram of the Kondo lattice model and the phase diagram of single-layer cuprates, simply by adjusting the interlayer coupling, allowing for detailed investigation of the relationship between these systems and opening possibilities for understanding the origins of unconventional superconductivity. While current analysis focuses on one-dimensional settings, the experimental framework is readily extendable to two dimensions and larger system sizes, promising further insights into complex quantum phenomena. 👉 More information 🗞 Connecting single-layer – to Kondo lattice models: Exploration with cold atoms 🧠 ArXiv: https://arxiv.org/abs/2512.09926 Tags: