Detector counting rate nonlinearity, though a known problem, is commonly ignored in the analysis of angle resolved photoemission spectroscopy where modern multichannel electron detection schemes using analog intensity scales are used. We focus on a n
early ubiquitous inverse saturation nonlinearity that makes the spectra falsely sharp and beautiful. These artificially enhanced spectra limit accurate quantitative analysis of the data, leading to mistaken spectral weights, Fermi energies, and peak widths. We present a method to rapidly detect and correct for this nonlinearity. This algorithm could be applicable for a wide range of nonlinear systems, beyond photoemission spectroscopy.
One of the most important properties of topological insulators (TIs) is the helical spin texture of the Dirac surface states, which has been theoretically and experimentally argued to be left-handed helical above the Dirac point and right handed heli
cal below. However, since the spin is not a good quantum number in these strongly spin-orbit coupled systems, this can not be a complete statement, and we must consider the total angular momentum J = L + S that is a contribution of the spin and orbital terms. Using a combination of orbital and spin-resolved angle-resolved photoemission spectroscopy (ARPES), we show a direct link between the different orbital and spin components, with a backwards spin texture directly observed for the in-plane orbital states of Bi2Se3.
We studied Sr2IrO4 and Sr3Ir2O7 using angle-resolved photoemission spectroscopy (ARPES), making direct experimental determinations of intra- and inter-cell coupling parameters as well as Mott correlations and gap sizes. The results are generally cons
istent with LDA+U+Spin-orbit coupling (SOC) calculations, though the calculations missed the momentum positions of the dominant electronic states and neglected the importance of inter-cell coupling on the size of the Mott gap. The calculations also ignore the correlation-induced spectral peak widths, which are critical for making a connection to activation energies determined from transport experiments. The data indicate a dimensionality-controlled Mott transition in these 5d transition-metal oxides (TMOs).
Topological insulators are novel macroscopic quantum-mechanical phase of matter, which hold promise for realizing some of the most exotic particles in physics as well as application towards spintronics and quantum computation. In all the known topolo
gical insulators, strong spin-orbit coupling is critical for the generation of the protected massless surface states. Consequently, a complete description of the Dirac state should include both the spin and orbital (spatial) parts of the wavefunction. For the family of materials with a single Dirac cone, theories and experiments agree qualitatively, showing the topological state has a chiral spin texture that changes handedness across the Dirac point (DP), but they differ quantitatively on how the spin is polarized. Limited existing theoretical ideas predict chiral local orbital angular momentum on the two sides of the DP. However, there have been neither direct measurements nor calculations identifying the global symmetry of the spatial wavefunction. Here we present the first results from angle-resolved photoemission experiment and first-principles calculation that both show, counter to current predictions, the in-plane orbital wavefunctions for the surface states of Bi2Se3 are asymmetric relative to the DP, switching from being tangential to the k-space constant energy surfaces above DP, to being radial to them below the DP. Because the orbital texture switch occurs exactly at the DP this effect should be intrinsic to the topological physics, constituting an essential yet missing aspect in the description of the topological Dirac state. Our results also indicate that the spin texture may be more complex than previously reported, helping to reconcile earlier conflicting spin resolved measurements.
