Bulk screening in core level photoemission from Mott-Hubbard and Charge-Transfer systems

We study optimally doped Bi$_{2}$Sr$_{2}$Ca$_{0.92}$Y$_{0.08}$Cu$_{2}$O$_{8+\delta}$ (Bi2212) using angle-resolved two-photon photoemission spectroscopy. Three spectral features are resolved near 1.5, 2.7, and 3.6 eV above the Fermi level. By tuning the photon energy, we determine that the 2.7-eV feature arises predominantly from unoccupied states. The 1.5- and 3.6-eV features reflect unoccupied states whose spectral intensities are strongly modulated by the corresponding occ...

Determining the doping level in high-temperature cuprate superconductors is crucial for understanding the origin of superconductivity in these materials and for unlocking their full potential. However, accurately determining the doping level remains a significant challenge due to a complex interplay of factors and limitations in various measurement techniques. In particular, in Bi$_{2}$Sr$_2$CuO$_{6+\delta}$ and Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, where the mobile carriers ar...

We study $1s$ and $2p$ hard x-ray photoemission spectra (XPS) in a series of late transition metal oxides: Fe$_2$O$_3$ (3$d^{5}$), FeTiO$_3$ (3$d^{6}$), CoO (3$d^{7}$) and NiO (3$d^{8}$). The experimental spectra are analyzed with two theoretical approaches: the MO$_6$ cluster model and the local density approximation (LDA) + dynamical mean-field theory (DMFT). Owing to the absence of the core-valence multiplets and spin-orbit coupling, 1$s$ XPS is found to be a sensitive pro...

Electronic properties of V$_2$OPO$_4$ have been investigated by means of hard x-ray photoemission spectroscopy (HAXPES) and subsequent theoretical calculations. The V 1$s$ and 2$p$ HAXPES spectra are consistent with the charge ordering of V$^{2+}$ and V$^{3+}$. The binding energy difference between the V$^{2+}$ and V$^{3+}$ components is unexpectedly large indicating large bonding-antibonding splitting between them in the final states of core level photoemission. The V 1$s$ H...

%auto-ignore This paper has been withdrawn by the authors because its results have been superceded by new experimental data and new theory presented in S.-K. Mo et al., cond-mat/0212110.

Photoemission spectra of the paramagnetic insulating (PI) phase of (V_0.972Cr_0.028)_2O_3, taken in ultra high vacuum up to the unusually high temperature (T) of 800 K, reveal a property unique to the Mott-Hubbard (MH) insulator and not observed previously. With increasing T the MH gap is filled by spectral weight transfer, in qualitative agreement with high-T theoretical calculations combining dynamical mean field theory and band theory in the local density approximation.

We discuss selected results from our recent work concerning the ARPES (angle-resolved photoemission) spectra from the cuprates. Our focus is on developing an understanding of the effects of the ARPES matrix element and those of strong electron correlations in analyzing photointensities. With simulations on Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212), we show that the ARPES matrix element possesses remarkable selectivity properties, such that by tuning the photon energy and po...

High temperature superconductivity in cuprates is realized by doping the Mott insulator with charge carriers. A central issue is how such an insulating state can evolve into a conducting or superconducting state when charge carriers are introduced. Here, by in situ vacuum annealing and Rb deposition on the Bi2Sr2Ca0.6Dy0.4Cu2O8+delta (Bi2212) sample surface to push its doping level continuously from deeply underdoped (Tc=25 K, doping level p-0.066) to the near zero doping par...

High-resolution hard X-ray photoemission measurements have been performed to clarify the electronic structure originating from the strong correlation between electrons in bulk Ce 3$d$ core-level spectra of CeNi$_{1-x}$Co$_x$Ge$_2$ (0 $\leq$ $x$ $\leq$ 1). In the Ce 3$d_{5/2}$ core-level spectra, the variation of satellite structures ($f^2$ peaks) shows that the hybridization strength between Ce 4$f$- and conduction electrons gradually increases with Co concentration in good a...

We studied the changes in the electronic structure of VO2 across the metal-insulator transition. The main technique was cluster model calculations with non-local screening channels. The calculation included a screening from a coherent state at the Fermi level in the metallic phase, and a screening from a Hubbard charge fluctuation within the V-V dimmer in the insulating phase. The calculation results are compared to previous photoemission and X-ray absorption spectra. The coh...