Laser angle-resolved photoemission as a probe of initial statekzdispersion, final-state band gaps, and spin texture of Dirac states in theBi2Te3topological insulator

Abstract

Angle-resolved photoemission spectroscopy (ARPES) is widely used to investigate topological states and their spin textures in topological materials. Here, the authors examine the role of the ARPES matrix element in laser-ARPES spectra, and delineate how imprints of the Dirac states and their spin textures are encoded in these spectra in terms of the character and symmetry of the underlying initial and final states. For this purpose, they collect laser-ARPES spectra from the exemplar topological insulator material Bi${}_{2}$Te${}_{3}$ over a wide range of momenta in the ${k}_{x}$-k${}_{y}$ plane at energies ranging from 5.57--6.70 eV for two different linear polarizations of the incident light. The experimental results are analyzed via first-principles fully relativistic calculations of ARPES intensities within the framework of the one-step model of photoemission. These include effects of the ARPES matrix element from a semi-infinite solid surface. The authors obtain new insight into the nature of the laser-ARPES spectra from topological materials, and show how these spectra contain fingerprints of the initial state ${k}_{z}$ dispersions and spin textures of the Dirac-cone states, and how laser-ARPES could open a previously unrecognized window on the presence of delicate gaps in the final-state spectra.