4 Search Results

We examine the bulk electronic structure of ${\mathrm{Nd}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ using Ni $2p$ core-level hard x-ray photoemission spectroscopy combined with density functional theory $+$ dynamical mean-field theory. Our results reveal a large deviation of the Ni $3d$ occupation from the formal ${\mathrm{Ni}}^{2.5+}$ valency, highlighting the importance of the charge transfer from oxygen ligands. We find that the dominant $d^8$more » configuration is accompanied by nearly equal contributions from $d^7$ and $d^9$ states, exhibiting an unusual valence state among Ni-based oxides. Finally, we discuss the Ni $d_{x^2-y^2}$ and $d_{z^2}$ orbital-dependent hybridization, correlation and local spin dynamics. Published by the American Physical Society 2025« less

We investigate the topological superconductor candidate ${\mathrm{UTe}}_2$ using high-resolution valence-band resonant inelastic x-ray scattering at the U  $M_{4,5}$ edges. We observe atomiclike low-energy excitations that support the correlated nature of this unconventional superconductor. These excitations originate from the U  $5f^2$ configuration, which is unexpected since the short Te2-Te2 distances exclude Te2 being $2-$ . By utilizing the photoionization cross-section dependence of the photoemission spectra in combination with band structure calculations, we infer that the stabilization ofmore » the U  $5f^2$ configuration is due to the U  $6d$ bonding states in the U dimers acting as a charge reservoir. Our results emphasize that the description of the physical properties should commence with a $5f^2$ ansatz. Published by the American Physical Society 2024« less

${\mathrm{CeRh}}_2{\mathrm{As}}_2$ is a new multiphase superconductor with strong suggestions for an additional itinerant multipolar ordered phase. The modeling of the low-temperature properties of this heavy-fermion compound requires a quartet ${\mathrm{Ce}}^{3+}$ crystal-field ground state. Here, we provide the evidence for the formation of such a quartet state using x-ray spectroscopy. Core-level photoelectron and x-ray absorption spectroscopy confirm the presence of Kondo hybridization in ${more »}_{}$ CeRh 2 As 2 . The temperature dependence of the linear dichroism unambiguously reveals the impact of Kondo physics for coupling the Kramer’s doublets into an effective quasiquartet. Nonresonant inelastic x-ray scattering data find that the $|{\mathrm{\Gamma }}_7^{-}⟩$ state with its lobes along the 110 direction of the tetragonal structure ( $xy$ orientation) contributes most to the multiorbital ground state of ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ . Published by the American Physical Society 2024« less

Using inelastic X-ray scattering beyond the dipole limit and hard X-ray photoelectron spectroscopy we establish the dual nature of the U 5f electrons in UM₂Si₂ (M = Pd, Ni, Ru, Fe), regardless of their degree of delocalization. We have observed that the compounds have in common a local atomic-like state that is well described by the U 5f² configuration with the $$Γ^{(1)}_1$$ and $$Γ_2$$ quasi-doublet symmetry. The amount of the U 5f³ configuration, however, varies considerably across the UM₂Si₂ series, indicating an increase of U 5f itineracy in going from M = Pd to Ni to Ru and to themore » Fe compound. The identified electronic states explain the formation of the very large ordered magnetic moments in UPd₂Si₂ and UNi₂Si₂, the availability of orbital degrees of freedom needed for the hidden order in URu₂Si₂ to occur, as well as the appearance of Pauli paramagnetism in UFe₂Si₂. A unified and systematic picture of the UM₂Si₂ compounds may now be drawn, thereby providing suggestions for additional experiments to induce hidden order and/or superconductivity in U compounds with the tetragonal body-centered ThCr₂Si₂ structure.« less