Unconventional high-energy-state contribution to the Cooper pairing in under-doped copper-oxide superconductor HgBa$_2$Ca$_2$Cu$_3$O$_{8+\delta}$

TL;DR

This study reveals an unconventional pairing mechanism in under-doped HgBa$_2$Ca$_2$Cu$_3$O$_{8+eta}$ superconductor, showing a peak-dip structure in Raman spectra linked to high-energy states and pseudogap interactions.

Contribution

It demonstrates the connection between high-energy electronic states and Cooper pairing in a cuprate superconductor through combined experimental and theoretical analysis.

Findings

Superconducting pair-breaking peak is linked with a dip disappearing at Tc.

Spectral weight shifts from the dip to the peak below Tc.

Cellular dynamical mean-field theory reproduces the experimental spectral features.

Abstract

We study the temperature-dependent electronic B1g Raman response of a slightly under-doped single crystal HgBa$_2$Ca$_2$Cu$_3$O$_{8+\delta}$ with a superconducting critical temperature Tc=122 K. Our main finding is that the superconducting pair-breaking peak is associated with a dip on its higher-energy side, disappearing together at Tc. This result hints at an unconventional pairing mechanism, whereas spectral weight lost in the dip is transferred to the pair-breaking peak at lower energies. This conclusion is supported by cellular dynamical mean-field theory on the Hubbard model, which is able to reproduce all the main features of the B1g Raman response and explain the peak-dip behavior in terms of a nontrivial relationship between the superconducting and the pseudo gaps.