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Empa Researchers Achieve Milestone in Quantum Physics with Nanographenes
In a groundbreaking development in 2024, researchers at Empa, in collaboration with their partners, have successfully realized a one-dimensional alternating Heisenberg model using synthetic materials for the first time. This quantum-physical model, which has been part of theoretical discussions for nearly a century, involves a linear chain of spins representing a unique form of quantum magnetism. The team, led by Roman Fasel, who heads the nanotech@surfaces laboratory at Empa, has also managed to reproduce the model’s counterpart in laboratory conditions.
The alternating Heisenberg model features spins connected in a distinct pattern of alternating strong and weak interactions, whereas in the newly developed homogeneous model, all spins are consistently linked. Despite this seemingly simple alteration, the implications are significant, yielding fundamentally different properties. In the homogeneous spin chain, the spins are highly interconnected and exhibit long-range correlations, with no energy gap separating the ground state from excited states. By contrast, the alternating model displays an energy gap and results in spins forming robust pairwise bonds, leading to a rapid reduction in correlations.
The research findings, which have been prominently published in the latest issue of Nature Materials, confirm these theoretical predictions through meticulous experimentation with nanographene spin chains.
Pioneering Quantum Technologies: Bridging Theory and Application
The empirical investigations into both Heisenberg models were executed using nanographenes, which are minuscule segments derived from the two-dimensional carbon structure known as graphene. By skillfully manipulating the geometry of these tiny fragments, the researchers are able to adjust their quantum physical characteristics. This endeavor aims to establish a versatile material platform for the experimental exploration of diverse quantum models and phenomena.
The experiments highlighting the Heisenberg models demonstrate the efficacy of this approach. For the alternating spin chain model, the team utilized a type of nanographene known as Clar’s goblets, hourglass-shaped molecules made up of eleven carbon rings. In contrast, the homogeneous Heisenberg chain was constructed from Olympicene, a nanographene comprising five rings, named for its resemblance to the iconic Olympic rings.
Fasel remarked, “This is the second instance in which we’ve shown that theoretical models of quantum physics can be realized using nanographenes, thereby making direct experimental testing of their predictions possible.” Looking ahead, the research team is eager to develop ferrimagnetic spin chains—where magnetic moments align oppositely but do not completely negate each other. The exploration of two-dimensional spin lattices is also on their agenda, particularly because these structures promise a greater diversity of quantum phases, including topological states and exotic phenomena, which hold vast potential for both basic research and practical implementations.
Recreating these theoretical models is far from a purely intellectual exercise; it is underpinned by a significant practical purpose. The advent of quantum technologies heralds potential advancements in areas such as communication, computational efficiency, and precision measurement. However, the fragile nature of quantum states poses challenges in fully understanding their implications, making research into practical applications critical. Through their innovative work with nanographenes, referred to as “quantum Lego,” Empa researchers aspire to unlock deeper insights into quantum effects and pave the way toward functional quantum technologies.
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