Determination of the time scale of photoemission from the measurement of spin polarization

Abstract

The Eisenbud-Wigner-Smith (EWS) time delay of photoemission depends on the phase term of the matrix element describing the transition. Because of an interference process between partial channels, the photoelectrons acquire a spin polarization which is also related to the phase term. The analytical model for estimating the time delay by measuring the spin polarization is reviewed in this manuscript. In particular, the distinction between scattering EWS and interfering EWS time delay will be introduced, providing an insight in the chronoscopy of photoemission. The method is applied to the recent experimental data for Cu(111) presented in M. Fanciulli et al., PRL 118, 067402 (2017), allowing to give better upper and lower bounds and estimates for the EWS time delays.

Spin- and angle-resolved photoemission on topological materials

“…It is important to note that diffraction or scattering at the surface will not change the modulus of the spin polarisation if a fully polarised beam is considered [94]. However, the surface could induce an additional rotation of the spin polarisation vector, although up to now no experimental evidence for a significant rotation has been found [45]. Therefore this effect will not be considered any further in this work.…”

“…To draw this conclusion further analysis is needed and for example the observation of a 100% spin polarisation signal in 3D SARPES is a very strong indication of spin-polarised initial states. A more detailed discussion of SARPES on spin degenerate initial states and their use can be found elsewhere 40 . The spin interference effects described above can create a spin polarisation that deviates from the expected purely helical spin texture, but also the initial state can obtain perpendicular components in the spin texture due to coupling to the crystal lattice as was already predicted and observed for Rashba systems 43,87 .…”

“…For atomic states this effect is well understood and can be used to explain a variety of effects [43]. For dispersive bands the basic mechanisms are similar, but the symmetry operations and description become much more complex [44,45]. In this review some of the most obvious consequences of this currently very active topic in SARPES will be covered.…”

“…To draw this conclusion further analysis is needed and for example the observation of a 100% spin polarisation signal in 3D SARPES is a very strong indication of spin-polarised initial states. A more detailed discussion of SARPES on spin degenerate initial states and their use can be found elsewhere [45].…”

Photoionization of Xe 5s: angular distribution and Wigner time delay in the vicinity of the second Cooper minimum

“…Looking at the time delay for specific polarizations of the photoelectron, especially relevant since spin-resolved measurements are now a reality [52][53][54], translates into calculating the derivatives of the phases of the transition amplitudes T 1± 10 m=1/2 5s , equations (9a) and (9b). The resulting spindependent time delays, using each of the three methodologies, are shown in figure 5 , however, are seen to exhibit a completely different phenomenology.…”