Band symmetries of GaSe(0001) studied by spin-resolved electron spectroscopy using circularly polarized radiation

Abstract

We have studied the symmetry properties of the bands of the layered semiconductor GaSe along the ⌬ direction by means of spin-resolved electron spectroscopy using circularly polarized synchrotron radiation and by means of a relativistic LAPW band-structure calculation. The photoelectron spectra show in the main a pair of weakly dispersing peaks caused by direct transitions from valence-band states with symmetries ⌬ 9 5 , ⌬ 9 6 and ⌬ 7 5 , ⌬ 8 6 . Our data determine the spin-orbit splitting of these valence bands to be ⌬E so ϭ0.3Ϯ0.1 eV. We find a gap in the unoccupied bands along ⌬ about 8 eV above the fundamental gap. The analysis of the photoelectron spin polarization reveals that also unoccupied states with low symmetries ⌬ 7 5 , ⌬ 8 6 and ⌬ 9 5 , ⌬ 9 6 are involved in excitation and emission. Spin resolved spectra measured at Auger electrons following the decay of Ga 3d core holes confirm that p derived unoccupied states exists below the vacuum level.

Effect of pressure on the structural properties and electronic band structure of GaSe

“…The ε polytype of GaSe was considered in recent DFT calculations of Refs. [28,29]. To our knowledge, the effect of pressure on the band structure of the ε polytype has not been calculated before, except for the band structure at 7 GPa given in Ref.…”

“…As for layered GaSe at ambient pressure, ab initio methods have been employed in lattice dynamics calculations [25] and in the interpretation of photoemission experiments [28,29]. It appears that fully relaxed ab initio calculations of the pressure-dependent structural or dynamical properties of layered GaSe have not been reported so far.…”

Observation of an underlying relativistic effect in the valence bands of Pt

“…Spin-resolved valence-band photoemission with circularly polarized light has been established as a unique tool to study the relativistic bulk band structures of nonmagnetic materials, where spin-orbit interaction plays an important role to modify the electronic bands which cannot be gleaned from spin integrated photoemission experiments [6][7][8]. Spin-resolved photoemission experiments with linearly or unpolarized light have no access to the bulk electronic band structure of nonmagnetic crystals because of spatial inversion symmetry in the bulk.…”

“…Before we present and discuss our results, the following group theoretical considerations are essential to gain a general insight into the electron spin polarization in the valence-band photoemission from the nonmagnetic centrosymmetric crystals in which spin-orbit interaction, time reversal symmetry and spatial inversion symmetry play crucial roles in determining the electron spin polarization [1][2][3][4][5]. It is well known that the existence of a nonzero spin polarization in the valence-band photoemission from nonmagnetic centrosymmetric crystals requires spin-orbit interaction either in the initial or in the final states [6][7][8][9][10]. Let us consider a general k vector in the Brillouin zone, where the point group of k contains only the identity element.…”