The Quest for New Superconductors: Exploring the Interplay of Itinerant Magnetism and Superconductivity

The Quantum Systems Accelerator (QSA) is at the forefront of groundbreaking research aimed at developing and co-designing the next generation of programmable quantum devices. In a collaborative effort between QSA institutions, Lawrence Berkeley National Laboratory (Berkeley Lab), and the University of California, Berkeley (UC Berkeley), scientists conducted a series of experiments with a novel layered 2D metal. The research focused on understanding the electronic behavior of this new material, with the goal of utilizing its unique properties in the fabrication of complex superconducting quantum processors. This interdisciplinary team leveraged the expertise of scientists across various fields and made use of state-of-the-art national capabilities and instrumentation at the Advanced Light Source and Molecular Foundry. The experimental results were published in the prestigious journal, Physical Review B, in December 2022.

The search for new superconducting 2D materials provides valuable insights into the challenges associated with fabricating superconducting quantum processors using conventional materials like aluminum, niobium, and silicon. Transition metal dichalcogenides (TMDs) are a class of exotic metals that can be fabricated into ultrathin layers with well-defined crystalline structures. These materials exhibit unique physical properties resulting from the interactions of their electrons. The tightly packed electrons can display behaviors such as superconductivity and itinerant magnetism. Superconductivity enables the flow of electrical charge with minimal resistance, while itinerant magnetism involves the transfer of magnetism among atoms. Traditionally, materials are either superconductors or magnets, but not both. However, TMDs offer the potential for finding materials with strong magnetic properties that are also superconducting. The extent to which itinerant magnetism and superconductivity coexist in TMDs has remained a topic of debate.

NiTa4Se8: A Promising Interconnected TMD

NiTa4Se8, a type of intercalated TMD with strongly correlated electrons, served as the focus of the experiments conducted by the QSA researchers. The presence of a ferromagnetic (nickel) layer in this material enhances the interaction and correlation between electrons, leading to interesting electronic conduction properties. The experimental lead, James Analytis, an associate professor at UC Berkeley and faculty scientist at Berkeley Lab, explained that studying materials with unique internal symmetries offers the potential for uncovering a different set of properties for quantum systems. By manipulating the atomic and electron arrangement through chemical processing and techniques, the researchers were able to study the behaviors of superconductivity and itinerant magnetism in NiTa4Se8.

To comprehensively analyze the properties of superconductivity and itinerant magnetism, the researchers needed to gain a deep understanding of the internal symmetries of NiTa4Se8. By synthesizing different symmetry configurations, the team could manipulate and control the behavior of electrons in the layered crystalline metal. The systematic experiments allowed for a detailed study of electron behavior by stacking and controlling them in the laboratory. Sinéad Griffin, a co-author of the paper and the QSA materials topical group research lead at the Molecular Foundry, emphasized the importance of discovering new superconductors for advancing quantum technologies. Griffin’s theoretical models and calculations guide the fabrication and characterization of materials at the lab, enabling the exploration of unknown physics and novel systems.

Advanced Instrumentation for Precise Measurements

Berkeley Lab’s cutting-edge photoelectron spectroscopy capabilities at the Advanced Light Source (ALS) played a crucial role in the research. These capabilities utilize photons to interact with electrons, enabling rapid characterization of 2D materials and surfaces. Techniques such as Angle-Resolved Photoemission Spectroscopy (ARPES) and Energy-dispersive X-ray spectroscopy (EDS or EDX) provided detailed insights into the electronic behavior and crystalline structure of NiTa4Se8 at a microscopic level. The ALS staff scientist and QSA researcher, Eli Rotenberg, with his expertise in photoelectron spectroscopy, carefully measured the behavior of electrons, including the Fermi surface, a critical energy level for superconductivity. Rotenberg explained that the interesting physics of crystalline materials lie at the interface between occupied and unoccupied states, where particles form moving waves that transmit energy information.

The complexity of the materials being studied requires advanced instrumentation and tools tailored to each specific system. As the materials may undergo changes or develop defects when integrated into quantum devices, the researchers face the challenge of finding new phenomena or results. Griffin highlighted the role of theoretical modeling in designing materials from fundamental key ingredients, enabling the discovery of unique properties. While NiTa4Se8 may not be the only magnetic TMD with correlated itinerant magnetism, the team’s findings indicate that exploring the interplay between itinerant magnetism and unconventional superconductivity in 2D materials can enhance our understanding and potentially lead to the fabrication of more advanced quantum processors.

The Future of Quantum Device Fabrication

The Quantum Systems Accelerator (QSA) team remains dedicated to solving the fabrication challenges that hinder the development of impactful quantum hardware systems. The integration of various techniques and synthesis capabilities, combined with the availability of cutting-edge facilities and instrumentation at Berkeley Lab, accelerates the transition from fundamental science to practical technologies. The QSA researchers emphasize the importance of exploring different materials and technologies to determine the most suitable approach for a given quantum device. With their unparalleled access to state-of-the-art capabilities and a singular vision, the QSA team has the opportunity to push the boundaries of quantum research and unlock new possibilities for future technologies.

The pioneering research conducted by the Quantum Systems Accelerator (QSA) in collaboration with Lawrence Berkeley National Laboratory and the University of California, Berkeley, brings us closer to understanding the interplay between itinerant magnetism and superconductivity in 2D materials. The exploration of novel materials such as NiTa4Se8 holds great promise for the development of improved superconducting quantum processors. As the world delves deeper into the realm of quantum technologies, the discoveries made by QSA are lighting the path towards a future powered by quantum devices.


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