Electronic structure of ternary palladates and effect of hole doping: a valence band photoemission spectroscopic study

Abstract

We investigate the electronic structure of ternary palladates APd3O4 (A = Sr, Ca) using valence band photoemission spectroscopy and band structure calculations. Energy positions of various features and overall width of the experimental valence band spectra are well captured by band structure calculations using hybrid functional. Band structure calculations within local density approximations lead to metallic ground state while the calculations using hybrid functional provide band gap of 0.25 eV and 0.22 eV for CaPd3O4 and SrPd3O4 respectively, suggesting moderate to strong electron correlation strength in these narrow band gap semiconducting palladates. High resolution spectra reveal negligibly small intensity at Fermi level, E F, for parent compounds, while hole doped SrPd3O4 (by 15% Li substitution at Sr site) exhibits a Fermi cut-off suggesting metallic character in contrast to semiconducting transport. These observations reveal the importance of localization of electrons in case where the Fermi edge falls in the mobility edge.

Revelation of Mott insulating state in layered honeycomb lattice Li$_2$RuO$_3$

“…1(b) shows the PDOS corresponding to O 2p and Ru 4d states from band structure calculations using YS-PBE0 functional. Screened hybrid functional have been shown to be very successful in capturing the band gap in correlated systems where the ground states are often found to be semiconducting or insulating [35][36][37]. These results exhibit an insulating ground state with the gap opening in the t 2g band; thus the E F has been set in the middle of the gap.…”

Revelation of Mott insulating state in layered honeycomb lattice Li2RuO3

“…Figure 1(b) shows the PDOS corresponding to O 2p and Ru 4d states from band structure calculations using YS-PBE0 functional. Screened hybrid functional have been shown to be very successful in capturing the band gap in correlated systems where the ground states are often found to be semiconducting or insulating [35][36][37]. These results exhibit an insulating ground state with the gap opening in the t 2g band; thus the E F has been set in the middle of the gap.…”

Evidence of electron correlation and weak bulk plasmon in SrMoO$_{3}$

“…The electron correlation is expected to be weak in 4d TMOs compared to 3d TMOs due to larger spatial extension of 4d orbitals than that of 3d orbitals. However, against this general belief, varying strength of electron correlation have been observed in 4d TMOs leading to exotic ground states [13][14][15][16][17][18][19][20][21][22][23] .…”

“…The methods beyond DFT, such as DFT-hybrid and DFT + DMFT, have been found to be quite successful in case of TMOs with varying strength of electron correlation. The hybrid functionals containing some part of the Hartree-Fock exchange have been very successful in correctly describing the electronic properties of many semiconductors 23,39,45 , insulators 39,46,47 and correlated metallic systems [48][49][50] . The mixing parameter α is related to the dielectric properties of a material and have been varied in order to match with the experimental results 51 even in case of metals 50 .…”