Rotational Phonons Drive Low-Energy Kinks in Cuprate Superconductors

TL;DR

This study demonstrates that rotational oxygen phonons significantly contribute to electron-phonon coupling in cuprate superconductors, explaining low-energy spectral features observed in ARPES experiments and advancing understanding of their microscopic mechanisms.

Contribution

The paper provides the first systematic DFT-based analysis showing rotational phonons as the dominant source of electron-phonon coupling in cuprates, aligning theoretical results with experimental spectral features.

Findings

Strong electron-phonon coupling with λ ≈ 0.5 in magnetic phase

Rotational oxygen phonons are the primary contributors to spectral kinks

Results agree with ARPES observations of low-energy anomalies

Abstract

Angle-resolved photoemission spectroscopy (ARPES) reveals ubiquitous quasiparticle ``kinks'' near $\sim$70 meV and $\sim$40 meV across cuprate superconductors, often accompanied by peak--dip--hump (PDH) structures. These features point to strong coupling between electrons and low-energy bosonic excitations, but the microscopic origin has remained elusive due to the limitations of conventional density-functional theory (DFT) and the high cost of beyond-DFT methods. Here, we systematically study the electron--phonon coupling (EPC) in hole-doped infinite-layer CaCuO$_2$ using the Strongly Constrained and Appropriately Normed (SCAN) density functional, explicitly including magnetic effects. We find a substantial EPC strength $\lambda$ of $\sim$0.5 in the magnetic phase, producing kinks and PDH structures in the 40-80~meV window in excellent agreement with experiments. The dominant contribution arises from rotational oxygen phonons, while breathing modes contribute little. Our results establish strong EPC in cuprates, highlight the key role of rotational phonons, and provide a framework for understanding spectral anomalies in cuprates and beyond.