Suppression of spectral gap and flat bands on a cuprate superconductor side-surface
Abstract
Side surfaces of cuprate superconductors are expected to display a suppressed d -wave order parameter and zero-energy topological flat bands with a large density of states, making them susceptible to symmetry broken orders. Yet such surfaces have never been investigated with momentum-resolved, surface-sensitive probes, because high-temperature superconductors rarely cleave along them. Using focused-ion-beam milling to define a controlled breaking point, we expose pristine (110) side surfaces of overdoped La 2− x Sr x CuO ₄ ( x = 0.22) suitable for angle-resolved photoemission. We do not resolve an opening or closing of a superconducting spectral gap within our energy resolution ( ~ 4 meV), in agreement with theoretical predictions. Surprisingly, the expected zero-energy flat band peak is also suppressed, despite the high topographic quality of the surface. Self-consistent Bogoliubov–de Gennes calculations show that the measured geometric roughness of the cleaved surface is too weak to eliminate these modes. The calculations further demonstrate that bulk inhomogeneities characteristic of high-temperature superconductors, modelled as moderate Anderson-type disorder, can broaden the flat-band states beyond detectability. Our results provide the first momentum-resolved view of the electronic structure on a cuprate side surface and identify disorder as a plausible mechanism obscuring the spectroscopic signatures of the predicted flat-band states.
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BibTeX
@article{domaine2026suppression,
title = {{Suppression of spectral gap and flat bands on a cuprate superconductor side-surface}},
author = {Gabriele Domaine and Mihir Date and Sydney K. Y. Dufresne and Natalie Lehmann and Daiyu Geng and Tohru Kurosawa and Amit Kumar and Jiaju Wang and Tianlun Yu and Chien-Ching Chang and Swosti P. Sarangi and Ding Pei and Yiran Liu and Julia Küspert and Shigemi Terakawa and Markel Pardo Almanza and Jiabao Yang and Izabela Biało and Matthew D. Watson and Timur K. Kim and Stephen M. Hayden and Kritika Singh and Banabir Pal and Matteo Minola and Johan Chang and Naoki Momono and Migaku Oda and Stuart S. P. Parkin and Andreas P. Schnyder and Niels B. M. Schröter},
journal = {Nature Communications},
year = {2026},
month = oct,
doi = {10.1038/s41467-026-78020-y},
url = {https://www.nature.com/articles/s41467-026-78020-y},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Suppression of spectral gap and flat bands on a cuprate superconductor side-surface
AU - Gabriele Domaine
AU - Mihir Date
AU - Sydney K. Y. Dufresne
AU - Natalie Lehmann
AU - Daiyu Geng
AU - Tohru Kurosawa
AU - Amit Kumar
AU - Jiaju Wang
AU - Tianlun Yu
AU - Chien-Ching Chang
AU - Swosti P. Sarangi
AU - Ding Pei
AU - Yiran Liu
AU - Julia Küspert
AU - Shigemi Terakawa
AU - Markel Pardo Almanza
AU - Jiabao Yang
AU - Izabela Biało
AU - Matthew D. Watson
AU - Timur K. Kim
AU - Stephen M. Hayden
AU - Kritika Singh
AU - Banabir Pal
AU - Matteo Minola
AU - Johan Chang
AU - Naoki Momono
AU - Migaku Oda
AU - Stuart S. P. Parkin
AU - Andreas P. Schnyder
AU - Niels B. M. Schröter
PY - 2026
DA - 2026/10/07
JO - Nature Communications
DO - 10.1038/s41467-026-78020-y
UR - https://www.nature.com/articles/s41467-026-78020-y
AB - Side surfaces of cuprate superconductors are expected to display a suppressed d -wave order parameter and zero-energy topological flat bands with a large density of states, making them susceptible to symmetry broken orders. Yet such surfaces have never been investigated with momentum-resolved, surface-sensitive probes, because high-temperature superconductors rarely cleave along them. Using focused-ion-beam milling to define a controlled breaking point, we expose pristine (110) side surfaces of overdoped La 2− x Sr x CuO ₄ ( x = 0.22) suitable for angle-resolved photoemission. We do not resolve an opening or closing of a superconducting spectral gap within our energy resolution ( ~ 4 meV), in agreement with theoretical predictions. Surprisingly, the expected zero-energy flat band peak is also suppressed, despite the high topographic quality of the surface. Self-consistent Bogoliubov–de Gennes calculations show that the measured geometric roughness of the cleaved surface is too weak to eliminate these modes. The calculations further demonstrate that bulk inhomogeneities characteristic of high-temperature superconductors, modelled as moderate Anderson-type disorder, can broaden the flat-band states beyond detectability. Our results provide the first momentum-resolved view of the electronic structure on a cuprate side surface and identify disorder as a plausible mechanism obscuring the spectroscopic signatures of the predicted flat-band states.
SN - 2041-1723
ER -