Proximity-induced nodal metal in an extremely underdoped CuO<sub>2</sub> plane in triple-layer cuprates.
basic_science · Level V
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- Record sourced from PubMed, PMID 41145421.
- Also identified by DOI 10.1038/s41467-025-64492-x and PMC identifier 12559703.
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Abstract
We performed angle-resolved photoemission spectroscopy studies on the triple-layer Bi<sub>2</sub>Sr<sub>2</sub>Ca<sub>2</sub>Cu<sub>3</sub>O<sub>10+δ</sub> over a wide doping range. Although the doping level of the inner CuO<sub>2</sub> plane is extremely low in underdoped samples, the d-wave SC gap is enhanced to the unprecedentedly large value of Δ<sub>0</sub> ~ 80-100 meV at the antinode. This gap persists well above T<sub>c</sub> without a Fermi arc, indicating a "nodal metal". We attribute the nodal metallic behavior to the unique local environment of the inner clean CuO<sub>2</sub> plane, sandwiched by nearly optimally-doped two outer planes and hence subject to strong proximity effect from both sides. In the nodal metal, quasiparticle peaks show electron-hole symmetry, suggesting d-wave pairing fluctuations. Thus the proximity effect on the innermost CuO<sub>2</sub> plane is the strongest in the triple-layer cuprates, which explains why the T<sub>c</sub> reaches the maximum at the layer number of three in every multi-layer cuprate family.