# Photoinduced filling of near nodal gap in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$

## TL;DR

This study uses time-resolved spectroscopy to investigate how photoexcitation affects the superconducting gap and quasiparticle dynamics in optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+eta}$, revealing gap stiffening and faster quasiparticle relaxation.

## Contribution

It provides new insights into the ultrafast dynamics of the superconducting gap and quasiparticles in a high-temperature superconductor under photoexcitation.

## Key findings

- Superconducting gap becomes slightly stiffer off the nodal direction.
- Nodal quasiparticles relax faster with higher photoexcitation fluence.
- Gap collapse and reformation dynamics are observed.

## Abstract

We report time and angle resolved spectroscopic measurements in optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. The spectral function is monitored as a function of temperature, photoexcitation density and delay time from the pump pulse. According to our data, the superconducting gap becomes slightly stiffer when moving off the nodal direction. The nodal quasiparticles develop a faster dynamics when pumping the superconductor with a fluence that is large enough to induce the total collapse of the gap. We discuss the observed relaxation in terms of a dynamical reformation of Cooper pairs.