Using the wave functions of the multichannel-quantum-defect theory, a semiclassical theory for both elastic and inelastic collisional cross sections of Rydberg atoms, in which there can be more than ...one valence electron, with ground-state rare-gas atoms is obtained. Especially the noble-gas-induced broadening cross sections of Rydberg series in alkaline-earth atoms can be calculated. An application of theory is shown to explain the irregular broadening rates of Sr 5{ital sns} {sup 1}{ital S}{sub 0} series due to collision with Xe, and a good agreement between theory and experiment is achieved.
We present energy-momentum mapping of surface Dirac photocurrent in the topological insulator Sb\(_2\)Te\(_3\) by means of time- and angle-resolved two-photon photoemission spectroscopy combined with ...polarization-variable mid-infrared pulse laser. It is demonstrated that the direct optical transition from the occupied to the unoccupied part of the surface Dirac-cone permits the linear and circular photogalvanic effect which thereby enables us to coherently control the surface electric-current by laser polarization. Moreover, the surface current mapping directly visualizes ultrafast current dynamics in the Dirac cone in the time domain. We unravel the ultrafast intraband relaxation dynamics of the inelastic scattering and momentum scattering separately. Our observations pave the pathway for coherent optical control over surface Dirac electrons in topological insulators.
Time- and angle-resolved two-photon photoemission (2PPE) was used to study the electronic structure and ultrafast electron dynamics of the p-doped topological insulator Sb sub(2)Te sub(3) and its ...derivative Sb sub(2)Te sub(2)S. Our 2PPE experiments directly reveal that the massless Diraccone like energy dispersion of topological surface states is realized above the Fermi energy in both materials. The observed bulk conduction bands of Sb sub(2)Te sub(2)S are found to be shifted to higher energies as compared to Sb sub(2)Te sub(3). This shift has, however, surprisingly almost no influence on the electron dynamics in the topological surface state, which proceed on a picosecond time scale.
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