A distinct bosonic mode in an electron-doped high-transition-temperature superconductor

TL;DR

This study uses high-resolution scanning tunnelling microscopy on an electron-doped superconductor to identify a bosonic mode likely originating from spin excitations, providing insights into the pairing mechanism of high-T c superconductors.

Contribution

It reports the detection of a bosonic mode in an electron-doped superconductor and suggests its electronic origin, advancing understanding of the pairing glue in high-T c superconductors.

Findings

Identified a bosonic mode at ~10.5 meV in PLCCO superconductor.

Mode energy correlates with spin-excitations rather than phonons.

Supports the hypothesis of spin-excitations as the pairing mechanism.

Abstract

Despite recent advances in understanding high-transition-temperature (high-T c) superconductors, there is no consensus on the origin of the superconducting 'glue': that is, the mediator that binds electrons into superconducting pairs. The main contenders are lattice vibrations (phonons) and spin-excitations with the additional possibility of pairing without mediators. In conventional superconductors, phonon-mediated pairing was unequivocally established by data from tunnelling experiments. Proponents of phonons as the high-T c glue were therefore encouraged by the recent scanning tunnelling microscopy experiments on hole-doped Bi2Sr2CaCu2O8-delta (BSCCO) that reveal an oxygen lattice vibrational mode whose energy is anticorrelated with the superconducting gap energy scale. Here we report high-resolution scanning tunnelling microscopy measurements of the electron-doped high-T c superconductor Pr0.88LaCe0.12CuO4 (PLCCO) (T c = 24 K) that reveal a bosonic excitation (mode) at energies of 10.5 plus/minus 2.5 meV. This energy is consistent with both spin-excitations in PLCCO measured by inelastic neutron scattering (resonance mode) and a low-energy acoustic phonon mode, but differs substantially from the oxygen vibrational mode identified in BSCCO. Our analysis of the variation of the local mode energy and intensity with the local gap energy scale indicates an electronic origin of the mode consistent with spin-excitations rather than phonons.