Fine Details of the Nodal Electronic Excitations in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$

TL;DR

This study uses high-resolution photoemission to reveal detailed low-energy electronic excitations in optimally doped Bi2212, showing changes across the superconducting transition and confirming a d-wave gap with finite bilayer splitting.

Contribution

It provides new insights into the nodal electronic excitations, including the temperature dependence of scattering rates and the nature of the superconducting gap in Bi2212.

Findings

Discontinuous change in scattering rates at T_C.

Cubic dependence of scattering rates on frequency and temperature in the superconducting state.

Finite bilayer splitting at the nodal point.

Abstract

Very high energy resolution photoemission experiments on high quality samples of optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ show new features in the low-energy electronic excitations. A marked change in the binding energy and temperature dependence of the near-nodal scattering rates is observed near the superconducting transition temperature, $T_C$. The temperature slope of the scattering rate measured at low energy shows a discontinuity at ~$T_C$. In the superconducting state, coherent excitations are found with the scattering rates showing a cubic dependence on frequency and temperature. The superconducting gap has a d-wave magnitude with negligible contribution from higher harmonics. Further, the bi-layer splitting has been found to be finite at the nodal point.