Wannier orbital theory and angle-resolved photoemission spectroscopy for the quasi-one-dimensional conductor LiMo6O17 . II. Intensity variations and the six t2g…

This is the second paper of a series of three papers presenting a combined study by band theory and angle-resolved photoemission spectroscopy (ARPES) of lithium purple bronze. The t2g Wannier orbitals (WOs) and resulting six-band tight-binding (TB) Hamiltonian found in paper I are used here to develop a theory of the ARPES intensity variations, including a selection rule whose validity relies on the smallness of and the cancellation between the displacement- and inversion-dimerizations of the zigzag chains (ribbons) in regions of the final-state wave vector κ. We then present the ARPES results for the band structure of the four occupied t2g bands (gapped $xz$, $yz$, and split metallic $xy$). A detailed comparison to the theory validates the selection rule. We present the Fermi surface as seen directly in the raw ARPES data, both parallel and perpendicular (using photon-energy dependence) to the sample surface, and show that the selection rule can enable separation of the barely split and highly quasi-one-dimensional $xy$ bands. We adjust the energy of the $xy$ WO energy by 0.1 eV (≈1/4 of the gap) with respect to that of the gapped $xz$ and $yz$ WOs and, in a second step, fine-tune merely seven out of the more than 40 TB parameters to achieve an excellent fit to the ARPES bands lying more than 0.15 eV below the Fermi level. So doing then also gives nearly perfect agreement closer to the Fermi level.