Unprecedentedly large gap in HgBa2Ca2Cu3O8+δ with the highest Tc at ambient pressure
Chuanhao Wen, Zhiyong Hou, Alireza Akbari, Kailun Chen, Wenshan Hong, Huan Yang, Ilya Eremin, Yuan Li, Hai‐Hu Wen
Abstract
In cuprate superconductors, the highest T c is possessed by the HgBa 2 Ca 2 Cu 3 O 8+δ (Hg-1223) system at ambient pressure, but the reason remains elusive. Here we report the scanning tunneling measurements on the Hg-1223 single crystals with T c ≈ 134 K. The observed gaps determined from the tunneling spectra (STS) can be categorized into two groups: the smaller gap Δ 1 ranges from about 45–70 meV, while the larger gap Δ 2 from about 65 to 98 meV. The STS was measured up to 200 K and the larger gap can persist well above T c , indicating a pseudogap feature which may reflect the strong pairing energy in the inner layer. Interestingly, an extremely strong particle-hole asymmetry is observed in associating with a very robust coherence-like peak at the bias of the larger gap in the hole branch of the Bogoliubov dispersion. We argue that the observed asymmetry results may be from the interplay of a flat band (van Hove singularity) in the electronic spectrum and the larger gap in the underdoped (inner) layer. A theoretical approach based on a trilayer model with an interlayer coupling can give a reasonable explanation. Our results provide deep insight into understanding the mechanism of superconductivity in cuprate superconductors.