Researchers Discover Subspace Decoupling in Two-orbital Lattices Driving Long-range Superconducting Pairing Correlations

The search for unconventional superconductivity continues to drive materials science, and new research offers a potential pathway to achieving this elusive state. Kiryl Pakrouski from the Institute for Theoretical Physics, ETH Zurich, and K. V. Samokhin investigate how specific interactions within materials can create isolated, dynamically stable regions that promote strong superconducting correlations. Their work demonstrates that these regions, termed ‘many-body scars’, can arise from relatively common interactions, such as chemical potential, Hubbard, and spin-orbit coupling, and support both spin-singlet and spin-triplet pairing. This discovery is significant because it suggests that unconventional superconductivity may be attainable in a broader range of materials than previously thought, potentially paving the way for new high-temperature superconductors and transformative technologies.

Researchers have identified specific quantum states distinguished by strong pairing correlations, offering new insights into unconventional superconductivity. These states, found within a two-orbital system of interacting particles, exhibit dynamically decoupled subspaces known as many-body scars. These scars support robust Cooper pairing, a crucial step towards understanding how superconductivity arises in certain materials.

Superconductivity, Pairing Mechanisms, and Multiband Systems

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Many-body Scars Enable Unconventional Superconductivity

Researchers have discovered a connection between weak ergodicity breaking and unconventional superconductivity, revealing how specific quantum states can exhibit robust pairing correlations. The team investigated a two-orbital system, demonstrating the existence of dynamically decoupled subspaces, known as many-body scars, that support unconventional Cooper pairing. These scars, formed by states invariant under certain transformations, exhibit long-range superconducting correlations significantly stronger than other states in the system. The findings demonstrate that these many-body scar states can possess an off-diagonal long-range order, a key characteristic of superconductivity, even with complex pairing interactions.

Researchers constructed these subspaces using combinations of two-electron and four-electron pairing, finding that a state resembling a BCS wavefunction could always be made the ground state with a pairing potential. Analytical results confirm that the properties of these scars are largely independent of the system’s structure, size, and dimensionality, a result validated through numerical calculations on small systems. This research extends previous work on specific pairing states, demonstrating that unconventional pairing can emerge within these dynamically isolated subspaces. The team proposes that these many-body scar states offer a new framework for understanding multiband and multi-orbital superconductivity, potentially explaining the behavior of materials like magnesium diboride, strontium ruthenate, and iron-based superconductors.

Scar States Enable Robust Pairing Correlations

This research demonstrates the existence of robust, spatially localized pairing correlations within a two-orbital system, arising from dynamically decoupled subspaces within the system’s quantum states. The team constructed these subspaces using interactions commonly found in two-orbital superconducting materials, such as chemical potential, Hubbard interactions, and spin-orbit coupling. Importantly, the analysis reveals a family of group-invariant “scar” states, which are highly stable and exhibit unique properties related to pairing and clustering, and can accommodate both spin-singlet and spin-triplet pairing. These scar states are characterized by a tower of energy levels, with the lowest-energy state closely resembling a BCS wavefunction, but extended to include higher-order pairing terms.

The researchers show that these states remain stable even when a superconducting gap is introduced, and can be understood through a transformation to Bogoliubov fermions. The findings suggest a pathway to unconventional superconductivity where pairing is localized and protected by the unique structure of these dynamically decoupled subspaces. The authors acknowledge that their analytical results are largely independent of system size and dimension, though numerical verification was limited to small systems. Future work could explore the behavior of these scar states in larger, more complex systems and investigate their potential role in stabilizing unconventional superconducting phases.