A method to separate the non‐resonant inelastic X‐ray scattering signal of a micro‐metric sample contained inside a diamond anvil cell (DAC) from the signal originating from the high‐pressure sample ...environment is described. Especially for high‐pressure experiments, the parasitic signal originating from the diamond anvils, the gasket and/or the pressure medium can easily obscure the sample signal or even render the experiment impossible. Another severe complication for high‐pressure non‐resonant inelastic X‐ray measurements, such as X‐ray Raman scattering spectroscopy, can be the proximity of the desired sample edge energy to an absorption edge energy of elements constituting the DAC. It is shown that recording the scattered signal in a spatially resolved manner allows these problems to be overcome by separating the sample signal from the spurious scattering of the DAC without constraints on the solid angle of detection. Furthermore, simple machine learning algorithms facilitate finding the corresponding detector pixels that record the sample signal. The outlined experimental technique and data analysis approach are demonstrated by presenting spectra of the Si L2,3‐edge and O K‐edge of compressed α‐quartz. The spectra are of unprecedented quality and both the O K‐edge and the Si L2,3‐edge clearly show the existence of a pressure‐induced phase transition between 10 and 24 GPa.
Spatially resolved signal collection enhances data quality of non‐resonant inelastic X‐ray scattering experiments dramatically. This new technique is demonstrated by presenting data from the O K‐ and Si L2,3‐edge of SiO2 α‐quartz at high pressure.
Spin-orbit entangled magnetic dipoles, often referred to as pseudospins, provide a new avenue to explore novel magnetism inconceivable in the weak spin-orbit coupling limit, but the nature of their ...low-energy interactions remains to be understood. We present a comprehensive study of the static magnetism and low-energy pseudospin dynamics in the archetypal spin-orbit Mott insulator Sr2IrO4. We find that in order to understand even basic magnetization measurements, a formerly overlooked in-plane anisotropy is fundamental. In addition to magnetometry, we use neutron diffraction, inelastic neutron scattering, and resonant elastic and inelastic x-ray scattering to identify and quantify the interactions that determine the global symmetry of the system and govern the linear responses of pseudospins to external magnetic fields and their low-energy dynamics. We find that a pseudospin-only Hamiltonian is insufficient for an accurate description of the magnetism in Sr2IrO4 and that pseudospin-lattice coupling is essential. This finding should be generally applicable to other pseudospin systems with sizable orbital moments sensitive to anisotropic crystalline environments.
We have studied local magnetic moment and electronic phase separation in superconducting K sub(x) Fe sub(2-y) Se sub(2) by x-ray emission and absorption spectroscopy. Detailed temperature-dependent ...measurements at the Fe K-edge have revealed coexisting electronic phases and their correlation with the transport properties. By cooling down, the local magnetic moment of Fe shows a sharp drop across the superconducting transition temperature (T sub(c)) and the coexisting phases exchange spectral weights with the low-spin state, gaining intensity at the expense of the higher-spin state. After annealing the sample across the iron-vacancy order temperature, the system does not recover the initial state and the spectral weight anomaly at T sub(c) as well as superconductivity disappear. The results clearly underline that the coexistence of the low-spin and high-spin phases and the transitions between them provide unusual magnetic fluctuations and have a fundamental role in the superconducting mechanism of the electronically inhomogeneous K sub(x) Fe sub(2-y) Se sub(2) system.
Using resonant inelastic x-ray scattering (RIXS) at the Cu L-absorption edge, we have observed intense, dispersive spin excitations in highly overdoped Tl sub(2)Ba sub(2)CuO sub(6 + delta ) ...(superconducting T sub(c) = 6 K), a model compound whose normal-state charge transport and thermodynamic properties have been shown to exhibit canonical Fermi-liquid behavior. Complementary RIXS experiments on slightly overdoped Tl sub(2)Ba sub(2)CuO sub(6 + delta ) (T sub(c) = 89 K) and on Y sub(1-x)Ca sub(x)Ba sub(2)Cu sub(3)O sub(6+ delta ) compounds spanning a wide range of doping levels indicate that these excitations exhibit energies and energy-integrated spectral weights closely similar to those of antiferromagnetic magnons in undoped cuprates, indicating the persistence of substantial antiferromagnetic spin correlations over a wide doping range. The surprising coexistence of such correlations with Fermi-liquid-like charge excitations in highly overdoped cuprates poses a challenge to current theoretical models of correlated-electron metals.
Recent theoretical predictions of “unprecedented proximity” of the electronic ground state of iridium fluorides to the SU(2) symmetric jeff=1/2 limit, relevant for superconductivity in iridates, ...motivated us to investigate their crystal and electronic structure. To this aim, we performed high-resolution x-ray powder diffraction, Ir L3-edge resonant inelastic x-ray scattering, and quantum chemical calculations on Rb2IrF6 and other iridium fluorides. Our results are consistent with the Mott insulating scenario predicted by Birol and Haule Phys. Rev. Lett. 114, 096403 (2015), but we observe a sizable deviation of the jeff=1/2 state from the SU(2) symmetric limit. Interactions beyond the first coordination shell of iridium are negligible, hence the iridium fluorides do not show any magnetic ordering down to at least 20 K. A larger spin-orbit coupling in iridium fluorides compared to oxides is ascribed to a reduction of the degree of covalency, with consequences on the possibility to realize spin-orbit-induced strongly correlated physics in iridium fluorides.
► We recall the interest of studying low-energy excitations in correlated electron systems using RIXS. ► We present the setup for high-resolution RIXS experiments at the Ir L3 edge at the ESRF. ► We ...discuss how the present setup can be adapted for all other 5d and rare-earths.
High energy-resolution resonant inelastic X-ray scattering (RIXS) at the L2,3 edges of 3d transition metal compounds has proved to be a very powerful technique for the study of elementary excitations of various nature. In the case of cuprates, in particular, it was realized that magnetic excitations can be directly accessed, thus complementing neutron scattering experiments. It is clearly desirable to extend this technique to 5d transition metal compounds, whose L2,3 edges lie in the hard X-ray energy range. In the case of Ir, the L3 edge is found at 11.215keV. To access excitations energies similar to those of magnetic excitations in cuprates, a resolving power better than ≈105 is needed. Here, we describe the hard X-ray RIXS set-up at the ID16 beam line at the European Synchrotron Radiation Facility (ESRF), suitable for L3 edge RIXS studies of Ir oxides, with a combined energy-resolution of 36meV, i.e. a resolving power of 3×105.
NaOsO3 undergoes a metal-insulator transition (MIT) at 410 K, concomitant with the onset of antiferromagnetic order. The excitation spectra have been investigated through the MIT by resonant ...inelastic x-ray scattering (RIXS) at the Os L3 edge. Low resolution (ΔE∼300meV) measurements over a wide range of energies reveal that local electronic excitations do not change appreciably through the MIT. This is consistent with a picture in which structural distortions do not drive the MIT. In contrast, high resolution (ΔE∼56meV) measurements show that the well-defined, low-energy magnons in the insulating state weaken and dampen upon approaching the metallic state. Concomitantly, a broad continuum of excitations develops which is well described by the magnetic fluctuations of a nearly antiferromagnetic Fermi liquid. By revealing the continuous evolution of the magnetic quasiparticle spectrum as it changes its character from itinerant to localized, our results provide unprecedented insight into the nature of the MIT in NaOsO3. In particular, the presence of weak correlations in the paramagnetic phase implies a degree of departure from the ideal Slater limit.
NaOsO3 hosts a rare manifestation of a metal-insulator transition driven by magnetic correlations, placing the magnetic exchange interactions in a central role. We use resonant inelastic x-ray ...scattering to directly probe these magnetic exchange interactions. A dispersive and strongly gapped (58 meV) excitation is observed, indicating appreciable spin-orbit coupling in this 5d3 system. The excitation is well described within a minimal model Hamiltonian with strong anisotropy and Heisenberg exchange (J1=J2=13.9meV). The observed behavior places NaOsO3 on the boundary between localized and itinerant magnetism.
We present a combined experimental and theoretical study of the elementary magnetic excitations in Ba2YIrO6 and Sr2YIrO6-the two most intensively discussed candidates for a new type of magnetic ...instability caused by exciton condensation. For both materials, high-resolution resonant inelastic x-ray scattering (RIXS) at the Ir L3 edge reveals sharp excitations around 370 and 650 meV energy loss, which we identify as triplet and quintet spin-orbit excitons. While the momentum-dependent RIXS spectra reveal that both the triplet and the quintet propagate coherently within the nonmagnetic background of the singlet sites, these modes remain fully gapped. The Ir-Ir exchange interactions in both double perovskites are therefore not strong enough to overcome the magnetic gap and, hence, our results exclude an intrinsic magnetic instability due to a condensation of magnetic excitations for both Ba2YIrO6 and Sr2YIrO6.
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