In this work we provide an exhaustive study of the photemission spectrum of paramagnetic FeO under pressure using a refined version of our recently derived many-body effective energy theory (MEET). We show that, within a nonmagnetic description of the paramagnetic phase, the MEET gives an overall good description of the photoemission spectrum at ambient pressure as well as the changes it undergoes by increasing pressure. In particular at ambient pressure the band gap opens between the mixed Fe $t_{2g}$ and O $2p$ states and the Fe 4s states and, moreover, a $d$-$d$ gap opens, which is compatible with a high-spin configuration (hence nonzero local magnetic moments as observed in experiment), whereas decreasing pressure the band gap tends to close, $t_{2g}$ states tend to become fully occupied and $e_{g}$ fully unoccupied, which is compatible with a low-spin configuration (hence a collapse of the magnetic moments as observed in experiment). This is a remarkable result, since, within a nonmagnetic description of the paramagnetic phase, the MEET is capable to correctly describe the photoemission spectrum and the spin configuration at ambient as well as high pressure. For comparison we report the band gap values obtained using density-functional theory with a hybrid functional containing screened exchange (HSE06) and a variant of the $GW$ method (self-consistent COHSEX), which are reliable for the description of the antiferromagnetic phase. Both methods open a gap at ambient pressure, although, by construction, they give a low-spin configuration; increasing pressure they correctly describes the band gap closing. We also report the photoemission spectrum of the metallic phase obtained with one-shot fully-dynamical $GW$ on top of LDA, which gives a spectrum very similar to DMFT results from literature.
We have performed an angle-resolved photoemission spectroscopy study of La$_{0.6}$Sr$_{0.4}$FeO$_3$ using {\it in situ} prepared thin films and determined its band structure. The experimental band dispersions could be well explained by an empirical band structure assuming the G-type antiferromagnetic state. However, the Fe 3d bands were found to be shifted downward relative to the Fermi level ($E_F$) by $\sim 1$ eV compared with the calculation and to form a (pseudo)gap of $\sim 1$ eV at $E_F$. We attribute this observation to a strong localization effect of doped holes due to polaron formatio…
A band structure description of the observed large band gaps and moments in both the antiferromagnetic (AFM) and paramagnetic (PM) phases of the classic NaCl-structure Mott insulators MnO, FeO, CoO, and NiO is provided by ordinary, single-determinant density functional theory method. As noted by previous authors, the ordered AFM phases already show in band theory significant band gaps. However, for the disordered PM phases the commonly used band model has been to assume the macroscopically observed, averaged NaCl structure, where all transition metal sites are forced to be symmetry-equivalent …
Synthetic powder, ore samples and mineral single crystals of goethite ($α-$FeOOH) were investigated with polarized Raman spectroscopy at temperatures from 300 K to 473 K. The symmetry of the vibrational modes, observed in different scattering configurations, was determined unequivocally. The assignment of the Raman-active modes to definite atomic vibrations is supported by two types of lattice-dynamical calculations: empirical shell-model and $\textit{ab initio}$ DFT. The temperature dependencies of the lineshape parameters of some Raman-active vibrations near to the antiferromagnetic-paramagn…
We have studied the electronic structure of epitaxially grown thin films of La$_{1-x}$Sr$_x$FeO$_3$ by {\it in-situ} photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS) measurements. The Fe 2$p$ and valence-band PES spectra and the O $1s$ XAS spectra of LaFeO$_3$ have been successfully reproduced by configuration-interaction cluster-model calculation and, except for the satellite structure, by band-structure calculation.From the shift of the binding energies of core levels, the chemical potential was found to be shifted downward as $x$ was increased. Among the three peaks …
We have measured the temperature dependence of the photoemission and x-ray absorption spectra of La$_{1-x}$Sr$_x$FeO$_3$ (LSFO) epitaxial thin films with $x=0.67$, where charge disproportionation ($3{Fe}^{3.67+}\to 2{Fe}^{3+}+ {Fe}^{5+}$) resulting in long-range spin and charge ordering is known to occur below $T_{CD}=190$ K. With decreasing temperature we observed gradual changes of the spectra with spectral weight transfer over a wide energy range of $\sim 5$ eV. Above $T_{CD}$ the intensity at the Fermi level ($E_F$) was relatively high compared to that below $T_{CD}$ but still much lower t…
Nowadays it has become feasible to perform angle-resolved photoemission spectroscopy (ARPES) measurements of transition-metal oxides with three-dimensional perovskite structures owing to the availability of high-quality single crystals of bulk and epitaxial thin films. In this article, we review recent experimental results and interpretation of ARPES data using empirical tight-binding band-structure calculations. Results are presented for SrVO$_3$ (SVO) bulk single crystals, and La$_{1-x}$Sr$_x$FeO$_3$ (LSFO) and La$_{1-x}$Sr$_x$MnO$_3$ (LSMO) thin films. In the case of SVO, from comparison of…
The valence band electronic structure of Pr$_{0.5}$Sr$_{0.5}$MnO$_3$ has been investigated across its paramagnetic metallic (PMM) - ferromagnetic metallic (FMM) - antiferromagnetic insulator (AFMI) transition. Using surface sensitive high resolution photoemission we have conclusively demonstrated the presence of a pseudogap of magnitude 80 meV in the near Fermi level electronic spectrum in the PMM and FMM phases and finite intensity at the Fermi level in the charge ordering (CO)-AFMI phase. The pseudogap behavior is explained in terms of the strong electron-phonon interaction and the formation…
Vanadium sesquioxide, V2O3, boasts a rich phase diagram whose description necessitates the accounting for many-body Coulomb correlations. Spectral properties of this compound have been successfully addressed within dynamical mean field theory to an extent that results of recent angle resolved photoemission experiments have been correctly predicted. While photoemission spectroscopy probes the occupied part of the one-particle spectrum, optical experiments measure transitions into empty states and thus provide complementary information. In this work, we focus on the optical properties of V2O3 in…
Electronic properties of kagome lattice have drawn great attention recently. In associate with flat-band induced by destructive interference and Dirac cone-type dispersion, abundant exotic phenomena have been theoretically discussed. The material realization of electronic kagome lattice is a crucial step towards comprehending kagome physics and achieving novel quantum phases. Here, combining angle-resolved photoemission spectroscopy, transport measurements and first-principle calculations, we expose a planar flat-band in paramagnetic YCr6Ge6 as a typical signature of electronic kagome lattice.…
We have studied the temperature dependence of the photoemission spectra of Pr$_{1-x}$Ca$_x$MnO$_3$ (PCMO) with $x=0.25$, 0.3 and 0.5. For $x=0.3$ and 0.5, we observed a gap in the low-temperature CE-type charge-ordered (CO) phase and a pseudogap with a finite intensity at the Fermi level ($E_F$) in the high-temperature paramagnetic insulating (PI) phase. Within the CO phase, the spectral intensity near $E_F$ gradually increased with temperature. These observations are consistent with the results of Monte Carlo simulations on a model including charge ordering and ferromagnetic fluctuations [H. …
We employ molecular beam epitaxy to stabilize Ba2IrO4 thin films and utilize in situ angle-resolved photoemission spectroscopy to investigate the evolution of its electronic structure through the Neel temperature TN. Our measurements indicate that dispersions of the relativistic Jeff=1/2 and 3/2 bands exhibit an unusual dichotomy in their behavior through the Neel transition. Although the charge gap survives into the paramagnetic state, only the Jeff=1/2 state exhibits a strong temperature dependence and its gap softens with increasing temperature approaching TN, while the nearly fully occupie…
The noncentrosymmetric ferromagnetic Weyl semimetal CeAlSi with simultaneous space-inversion (SI) and time-reversal (TR) symmetry breaking provides a unique platform for the exploration of novel topological states. Here, by employing electrical and thermoelectrical transport, angle-resolved photoemission spectroscopy (ARPES), high-pressure techniques, and band calculations, we demonstrate that magnetism and pressure can serve as efficient parameters to tune the positions of Weyl nodes in CeAlSi. At ambient pressure, an anomalous Hall effect (AHE) and an anomalous Nernst effect (ANE) arise in t…
