47 research outputs found

### Intra-layer doping effects on the high-energy magnetic correlations in NaFeAs

We have used Resonant Inelastic X-ray Scattering (RIXS) and dynamical
susceptibility calculations to study the magnetic excitations in
NaFe$_{1-x}$Co$_x$As (x = 0, 0.03, and 0.08). Despite a relatively low ordered
magnetic moment, collective magnetic modes are observed in parent compounds (x
= 0) and persist in optimally (x = 0.03) and overdoped (x = 0.08) samples.
Their magnetic bandwidths are unaffected by doping within the range
investigated. High energy magnetic excitations in iron pnictides are robust
against doping, and present irrespectively of the ordered magnetic moment.
Nevertheless, Co doping slightly reduces the overall magnetic spectral weight,
differently from previous studies on hole-doped BaFe$_{2}$As$_{2}$, where it
was observed constant. Finally, we demonstrate that the doping evolution of
magnetic modes is different for the dopants being inside or outside the Fe-As
layer.Comment: 19 pages, 7 figure

### Orbital breathing effects in the computation of x-ray d-ion spectra in solids by ab initio wave-function-based methods

In existing theoretical approaches to core-level excitations of
transition-metal ions in solids relaxation and polarization effects due to the
inner core hole are often ignored or described phenomenologically. Here we set
up an ab initio computational scheme that explicitly accounts for such physics
in the calculation of x-ray absorption and resonant inelastic x-ray scattering
spectra. Good agreement is found with experimental transition-metal $L$-edge
data for the strongly correlated $d^9$ cuprate Li$_2$CuO$_2$, for which we
determine the absolute scattering intensities. The newly developed methodology
opens the way for the investigation of even more complex $d^n$ electronic
structures of group VI B to VIII B correlated oxide compounds

### Electron-lattice interactions strongly renormalize the charge transfer energy in the spin-chain cuprate Li$_2$CuO$_2$

Strongly correlated insulators are broadly divided into two classes:
Mott-Hubbard insulators, where the insulating gap is driven by the Coulomb
repulsion $U$ on the transition-metal cation, and charge-transfer insulators,
where the gap is driven by the charge transfer energy $\Delta$ between the
cation and the ligand anions. The relative magnitudes of $U$ and $\Delta$
determine which class a material belongs to, and subsequently the nature of its
low-energy excitations. These energy scales are typically understood through
the local chemistry of the active ions. Here we show that the situation is more
complex in the low-dimensional charge transfer insulator
Li$_\mathrm{2}$CuO$_\mathrm{2}$, where $\Delta$ has a large non-electronic
component. Combining resonant inelastic x-ray scattering with detailed
modeling, we determine how the elementary lattice, charge, spin, and orbital
excitations are entangled in this material. This results in a large
lattice-driven renormalization of $\Delta$, which significantly reshapes the
fundamental electronic properties of Li$_\mathrm{2}$CuO$_\mathrm{2}$.Comment: Nature Communications, in pres

### Single- and Multimagnon Dynamics in Antiferromagnetic $\alpha$-Fe$_2$O$_3$ Thin Films

Understanding the spin dynamics in antiferromagnetic (AFM) thin films is
fundamental for designing novel devices based on AFM magnon transport. Here, we
study the magnon dynamics in thin films of AFM $S=5/2$ $\alpha$-Fe$_2$O$_3$ by
combining resonant inelastic x-ray scattering, Anderson impurity model plus
dynamical mean-field theory, and Heisenberg spin model. Below 100 meV, we
observe the thickness-independent (down to 15 nm) acoustic single-magnon mode.
At higher energies (100-500 meV), an unexpected sequence of equally spaced,
optical modes is resolved and ascribed to $\Delta S_z = 1$, 2, 3, 4, and 5
magnetic excitations corresponding to multiple, noninteracting magnons. Our
study unveils the energy, character, and momentum-dependence of single and
multimagnons in $\alpha$-Fe$_2$O$_3$ thin films, with impact on AFM magnon
transport and its related phenomena. From a broader perspective, we generalize
the use of L-edge resonant inelastic x-ray scattering as a multispin-excitation
probe up to $\Delta S_z = 2S$. Our analysis identifies the spin-orbital mixing
in the valence shell as the key element for accessing excitations beyond
$\Delta S_z = 1$, and up to, e.g., $\Delta S_z = 5$. At the same time, we
elucidate the novel origin of the spin excitations beyond the $\Delta S_z = 2$,
emphasizing the key role played by the crystal lattice as a reservoir of
angular momentum that complements the quanta carried by the absorbed and
emitted photons.Comment: Accepted in Physical Review

### Determining the Short-Range Spin Correlations in Cuprate Chain Materials with Resonant Inelastic X-ray Scattering

We report a high-resolution resonant inelastic soft x-ray scattering study of
the quantum magnetic spin-chain materials Li2CuO2 and CuGeO3. By tuning the
incoming photon energy to the oxygen K-edge, a strong excitation around 3.5 eV
energy loss is clearly resolved for both materials. Comparing the experimental
data to many-body calculations, we identify this excitation as a Zhang-Rice
singlet exciton on neighboring CuO4-plaquettes. We demonstrate that the strong
temperature dependence of the inelastic scattering related to this high-energy
exciton enables to probe short-range spin correlations on the 1 meV scale with
outstanding sensitivity.Comment: 5 pages, 4 figure