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Register a new userCharge correlation in V$_2$OPO$_4$ probed by hard x-ray photoemission spectroscopy
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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$s$ HAXPES spectrum exhibits a charge transfer satellite which can be analyzed by configuration interaction calculations on a V$_2$O$_9$ cluster. The V 3$d$ spectral weight near the Fermi level is assigned to the 3$d$ $t_{2g}$ orbitals of the V$^{2+}$ site. The broad V 3$d$ spectral distribution is consistent with the strong hybridization between V$^{2+}$ and V$^{3+}$ in the ground state. The core level and valence band HAXPES results indicate substantial charge transfer from the V$^{2+}$ site to the V$^{3+}$ site.7 figure
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V 3$d$ charge and orbital states in V$_2$OPO$_4$ have been investigated by means of x-ray absorption spectroscopy (XAS). The electronic structure of V$_2$OPO$_4$ is very unique in that the charge transfer between V$^{2+}$ and V$^{3+}$ in face sharing VO$_6$ chains provides negative thermal expansion as reported by Pachoud {it et al.} [J. Am. Chem. Soc. {bf 140}, 636 (2018).] The near edge region of O 1$s$ XAS exhibits the three features which can be assigned to transitions to O 2$p$ mixed into the unoccupied V 3$d$ $t_{2g}$ and $e_{g}$ orbitals of V$^{2+}$ and V$^{3+}$. The V 2$p$ XAS line shape can be reproduced by multiplet calculations for a mixed valence state with V$^{2+}$ and V$^{3+}$. The polarization dependence of the O 1$s$ and V 2$p$ XAS spectra indicates V 3$d$ orbital order in which $xy$ and $yz$ (or $zx$) orbitals are occupied at the V$^{3+}$ site in the face sharing chains. The occupied $xy$ orbital is essential for the antiferromagnetic coupling between the V$^{2+}$ and V$^{3+}$ sites along the chains while the occupied $yz$ (or $zx$) orbital provides the antiferromagnetic coupling between the V$^{2+}$ and V$^{3+}$ sites between the chains.
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Bulk-sensitive hard x-ray photoemission spectroscopy (HAXPES) reveals for as-grown epitaxial films of half-metallic ferromagnetic CrO2(100) a pronounced screening feature in the Cr 2p3/2 core level and an asymmetry in the O 1s core level. This gives evidence of a finite, metal-type Fermi edge, which is surprisingly not observed in HAXPES. A spectral weight shift in HAXPES away from the Fermi energy is attributed to single-ion recoil effects due to high energy photoelectrons. In conjunction with inverse PES the intrinsic correlated Mott-Hubbard-type electronic structure is unravelled, yielding an averaged Coulomb correlation energy Uav ~ 3.2 eV.
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