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A remarkable collaboration between the National Science and Technology Council (NSTC) and a research team spearheaded by Distinguished Professor Chung-Hou Chung at the Department of Electrophysics, National Yang-Ming Chiao-Tung University, Taiwan, and researchers at the prestigious Brookhaven National Laboratory (BNL) in the United States, has led to a groundbreaking discovery.
The once-elusive nature of quantum critical entangled strange metal states in rare-earth superconductors has been unveiled, illuminating a path toward comprehending the mechanisms underpinning high-temperature superconductors.
The phenomenon of “strange metals” has baffled researchers for over thirty years. Unlike traditional metals, which exhibit resistance that decreases in a temperature-square pattern as they approach superconductivity, strange metals defy this convention.
These unusual materials manifest linear-in-temperature resistance and logarithmic-in-temperature divergent specific heat coefficients. The most intriguing of these states, known as the “Planckian metal” state, reveals a linear-in-temperature scattering rate inversely proportional to the Planck constant.
The enigmatic behaviours were discovered in various quantum materials, including rare-earth superconductors, high-temperature cuprate superconductors, organic superconductors, and two-dimensional twisted bi-layer graphene.
However, the mechanisms responsible for these strange metal states have remained shrouded in mystery, presenting an outstanding challenge in condensed matter physics. The research team, driven by a fervent dedication to unveil the secrets of these quantum states of matter, embarked on an ambitious quest to decipher the underlying mechanisms.
Quantum mechanics dictates that near quantum phase transition points, or quantum critical points, competing quantum ground states lead to unstable quantum critical states. These states, characterised by maximal quantum entanglement between electrons, include the strange metal state.
These are effectively new forms of matter, defined by “quantum entangled many-body states,” a result of enhanced quantum critical fluctuations at low temperatures. Beyond the realms of familiar metals, insulators, superconductors, and semiconductors, this introduces the intriguing concept of a “quantum critical state” as a fundamental form of matter.
The research endeavour centred on the Planckian metal state in strongly correlated rare-earth superconductors represents a triumphant union of theoretical and experimental collaboration. Empirical evidence solidified the Planckian metal state as a genuine quantum critical state adjacent to the quantum critical point.
Further, the research team proposed a microscopic theoretical framework grounded in quantum critical charge fluctuations and the “quantum many-body entanglement” between electron charge and spin degrees of freedom. This innovative theory successfully elucidates the Planckian metal state and its intricate relation to quantum critical phenomena in unconventional superconductors.
Not only is this advancement significant for the advancement of fundamental scientific knowledge, but it also bears relevance for technological applications. Understanding the behaviour of strange metals is a pivotal step in designing, predicting, and ultimately elevating the critical temperature of high-temperature superconductors.
This has profound implications for energy conservation, innovations in electrical power transmission with minimal energy loss, as well as the development of quantum computing and quantum information technologies.
Additionally, the study, creation, and practical use of superconductors are greatly aided by digital technology. Utilising digital tools for simulation and modelling is one important feature. To simulate and model the behaviour of superconductors at the atomic and quantum levels, researchers use cutting-edge computational techniques. This allows researchers to understand the underlying physics, forecast material characteristics, and create novel superconducting materials with certain qualities.
Also, data analysis is a crucial function of digital technology in the field of superconductors. Manual interpretation of complex experimental results from superconducting materials can be difficult. Researchers use advanced computational tools and algorithms to address this. These online tools support the analysis of experimental data, enabling researchers to pinpoint key variables, improve output, and unearth novel superconductor phenomena.