Particle–hole asymmetric superconducting coherence peaks in overdoped cuprates

As doping increases in cuprate superconductors, the superconducting transition temperature increases to a maximum at the so-called optimal doping, and then decreases in the overdoped regime. In the past few decades, research has primarily focused on the underdoped and optimally doped regions of the phase diagram. Here, phenomena such as the pseudogap and strange metal non-superconducting states make it difficult to determine the superconducting pairing mechanism. More recently, experiments have shown unconventional behaviour in strongly overdoped cuprates, in both the normal and superconducting states. However, a real-space investigation of the unconventional superconductivity in the absence of the pseudogap is lacking, and the superconductor-to-metal phase transition in the overdoped regime remains controversial. Here we use scanning tunnelling microscopy to investigate the atomic-scale electronic structure of overdoped Bi 2 Sr 2 Ca n − 1 Cu n O 2 n + 4 + δ cuprates. We show that, at low energies, the spectroscopic maps are well described by dispersive d -wave quasiparticle interference patterns. However, as the bias increases to the superconducting coherence peak energy, a periodic and non-dispersive pattern emerges. The position of the coherence peaks exhibits particle–hole asymmetry that modulates with the same period. We propose that this behaviour is due to quasiparticle interference caused by pair-breaking scattering between flat antinodal Bogoliubov bands. Cuprates that are doped beyond the point that optimizes the critical temperature were thought to be understood. Now, a careful real-space investigation shows unconventional behaviour in the superconducting state caused by pair-breaking scattering.