This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Superconductors are materials that carry electrical current with zero resistance below a specific critical temperature. In conventional superconductors, the transition to superconductivity generally occurs at very low temperatures.
Some unconventional superconductors, however, enter their superconducting phase at comparatively higher critical temperatures. This could be advantageous for practical applications, as superconductivity at higher temperatures could reduce the need for complex and expensive cooling systems. However, these materials generally still require substantial cooling.
Researchers at Nanjing University, the University of Science and Technology of China, the Hong Kong Polytechnic University and other institutes in China recently investigated the electronic processes underpinning superconductivity in La₃Ni₂O₇, a nickelate that has exhibited superconductivity at temperatures of up to around 80 K (-193°C, -316°F) under very high pressure. The evidence they collected, published in Nature Physics, suggests that superconductivity in specially engineered La₃Ni₂O₇-based films could arise from an electron-pairing mechanism distinct from the d-wave pairing associated with cuprate superconductors. "The discovery of superconductivity in bilayer nickelates has sparked widespread interest, providing a novel platform to explore unconventional high-temperature superconductivity," Prof.
Donglai Feng, co-senior author of the paper, told Phys.org. "Unlike cuprates, where the low-energy physics is largely governed by a single Cu 3dₓ²₋ᵧ² orbital with a d⁹ electronic configuration, bilayer nickelates feature a d⁷‧⁵ configuration where both Ni 3dₓ²₋ᵧ² and 3dᶻ² orbitals sit close to the Fermi level. This multiband nature raises fundamental questions regarding the pairing mechanism, sparking extensive theoretical and experimental debate." The researchers wanted to better understand how superconductivity emerges in bilayer nickelates.
To achieve this, they tried to answer two key research questions. "First, does the Ni 3dz2-dominated γ band actually cross the Fermi level, and what is its role in superconductivity?" said Prof. Yuefeng Nie, co-senior author of the paper.
"Second, what is the exact pairing symmetry of the superconducting gap? Addressing these questions required direct, momentum-resolved spectroscopic measurements in the superconducting state—a major experimental gap prior to our work." Superconductors exhibit a so-called superconducting gap, a forbidden range of electron energies that opens when electrons form superconducting pairs (i.e., Cooper pairs). One technique that can help probe this gap is called angle-resolved photoemission spectroscopy (ARPES).
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