Figure 3
From: Electronic structure and relaxation dynamics in a superconducting topological material
Relaxation mechanism.
(a) TRARPES images of Sr0.06Bi2Se3 before and after the pump pulse. Top panels show band dispersions obtained with the difference to the image before pumped and bottom panels show the time-evolution spectra. (b) ARPES band dispersion of Sr0.06Bi2Se3 at a positive time delay along the 
high-symmetry direction. The blue rectangles represent the integration window of transient photoemission intensity for Dirac surface state and 2D states. (c) Ultrafast evolution of the population of 2D quantum well states (black curve) and surface states (red for left surface state and blue for right surface state) for Sr0.06Bi2Se3. 2D quantum-well states relax faster than topological surface states. (d) Exponential fitting for the decay curves; fitting parameters are given in the Table. We only consider the decay of the carriers. The rise of the carriers are almost identical within the time-resolution. (e) Schematic view of the decay mechanism, where blue line represents the density of Dirac quasiparticles and red line corresponds to the density of surface 2D state, while dashed grey lines indicate the energy of the phonon mode. The surface phonon modes mostly strongly coupled to the surface Dirac quasiparticles are located at near 7.4 meV, marked with dashed lines. The thick magenta lines represent the vibrational mode of Sr, which is found to be about 14.12 meV.
