Angle-resolved photoemission studies of quantum materials

The Role of Orbital Nesting in the Superconductivity of Iron-Based Superconductors

“…The gap equation for the multiorbital model can be computed numerically by taking into account the singlet pairing vertex as an eigenvalue problem in which the largest eigenvalue leads to the highest transition temperature and its eigenfunction determines the symmetry of the gap (see, e.g., [5,8,9,26]). An anisotropic sign changing s-wave, s ± , is found as the dominant symmetry for system parameters compatible with moderately doped IBSs, in agreement with experiments, e.g., [12,[27][28][29]. A nearly degenerate d x 2 −y 2 state was discussed in [5,9] and could be relevant to explain Raman experiments in K-doped BaFe 2 As 2 [30][31][32][33], CaKFe 4 As 4 [34], and (Li 1−x Fe x )OHFeSe [35].…”

“…By comparing our results to analogous microscopic five-orbital calculations, we show that the OSSF model reproduces all the relevant features characterizing the RPA spin susceptibilities obtained within multiorbital models. The analysis of the SC vertex mediated by OSSF and of the corresponding gap equations results in anisotropic s ± gap functions that can present accidental nodes in agreement with multiorbital calculations and experiments [11,12], as well as an SC d x 2 −y 2 state nearly degenerate with the s ± , as previously discussed in, e.g., [5,9]. The main advantage of the simplified description provided by the OSSF model is that a precise connection between the features of the gap functions and the orbital make-up of the nested Fermi surfaces can be made.…”

“…The inclusion of the orbital degree of freedom in the analysis of the SC gaps allows reproducing a number of features experimentally observed in IBSs [12] such as the angular modulation of the s ± gap functions and the possibility of accidental nodes on the Fermi surfaces. On the other hand, the number of orbitals included makes the analysis of superconductivity within multiorbital models very complex.…”

Colloquium: Nonthermal pathways to ultrafast control in quantum materials

“…To achieve this leap, inspiration can be drawn from other fields, where such an integrated approach has already been established. Namely, an increased feedback between experimental characterization, theoretical understanding, and materials synthesis is a strategy that is successful employed in many branches of quantum materials research, for instance in the field of oxides (Coll et al, 2019), or in the study of quantum materials with angle-resolved photoemission spectroscopy (Sobota et al, 2021). This interdisciplinary approach requires additional effort, as a common language and concepts need to be developed for thinking about the underlying physics.…”

Orbital contributions in the element-resolved valence electronic structure of Bi2Se3

“…Numerous studies using synchrotron-based angle-resolved photoemission spectroscopy (ARPES) with excitation energies of 20-150 eV have been employed to study the electronic properties of this family of 3D TIs [1]. Low-energy ARPES is one of the key experimental techniques for investigating the electronic structure of TIs and its high energy resolution shows strength in resolving the topological and electronic states in the valence band (VB) [9][10][11]. However, the short inelastic mean-free path of photoelectrons limits the probing depth, adding an extra challenge to differentiate the bulk and surface electronic structure.…”