Lifetimes of excited electrons in Ta: Experimental time-resolved photoemission data and first-principlesGW+Ttheory

Time-resolved two-photon photoemission spectroscopy and first-principles GW and $\mathrm{GW}+\mathrm{T}$ theories have been used to study excited electron lifetimes in tantalum. The $\mathrm{GW}+\mathrm{T}$ approach includes evaluation of the lowest self-energy term of the many-body perturbation theory in the GW approximation and higher terms in the $T$-matrix approximation. The $\mathrm{GW}+\mathrm{T}$ calculated lifetimes are in good agreement with the measured lifetimes at excitation energies above $1.6\mathrm{eV}$. At lower energies, a slightly worse agreement between theoretical and experimental data is obtained which we refer to as the influence of cascade processes.