| 1. |
- Ferrario, M., et al.
(författare)
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IRIDE : Interdisciplinary research infrastructure based on dual electron linacs and lasers
- 2014
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 740, s. 138-146
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the scientific aims and potentials as well as the preliminary technical design of RUDE, an innovative tool for multi-disciplinary investigations in a wide field of scientific, technological and industrial applications. IRIDE will be a high intensity "particles factory", based on a combination of high duty cycle radio-frequency superconducting electron linacs and of high energy lasers. Conceived to provide unique research possibilities for particle physics, for condensed matter physics, chemistry and material science, for structural biology and industrial applications, IRIDE will open completely new research possibilities and advance our knowledge in many branches of science and technology. [RIDE is also supposed to be realized in subsequent stages of development depending on the assigned priorities.
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| 2. |
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| 3. |
- Steeneken, P. G., et al.
(författare)
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Crossing the gap from p- to n-type doping : Nature of the states near the chemical potential in La2-xSrxCuO4 and Nd2-xCexCuO4-delta
- 2003
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 90:24
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Tidskriftsartikel (refereegranskat)abstract
- We report on an x-ray absorption and resonant photoemission study on single crystals of the high-T-c cuprates La2-xSrxCuO4 and Nd2-xCexCuO4-delta. Using an intrinsic energy reference, we find that the chemical potential of La2-xSrxCuO4 lies near the top of the La2CuO4 valence band whereas in Nd2-xCexCuO4-delta it is situated near the bottom of the Nd2CuO4 conduction band. The data clearly establish that the introduction of Ce in Nd2CuO4 results in electrons being doped into the CuO2 planes. We infer that the states closest to the chemical potential have a Cu 3d(10) singlet origin in Nd2-xCexCuO4-delta and a 3d(9) (L) under bar singlet origin in La2-xSrxCuO4.
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| 4. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Dynamical charge density fluctuations pervading the phase diagram of a Cu-based high-Tc superconductor
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 365:6456, s. 906-910
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Tidskriftsartikel (refereegranskat)abstract
- Charge density modulations have been observed in all families of high–critical temperature (Tc) superconducting cuprates. Although they are consistently found in the underdoped region of the phase diagram and at relatively low temperatures, it is still unclear to what extent they influence the unusual properties of these systems. Using resonant x-ray scattering, we carefully determined the temperature dependence of charge density modulations in YBa2Cu3O7–d and Nd1+xBa2–xCu3O7–d for several doping levels. We isolated short-range dynamical charge density fluctuations in addition to the previously known quasi-critical charge density waves. They persist up to well above the pseudogap temperature T*, are characterized by energies of a few milli–electron volts, and pervade a large area of the phase diagram.
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| 5. |
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| 6. |
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| 7. |
- Ghiringhelli, G., et al.
(författare)
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Probing the singlet character of the two-hole states in cuprate superconductors
- 2002
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 312, s. 34-35
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Tidskriftsartikel (refereegranskat)abstract
- Using spin-resolved resonant photoemission we have probed the singlet vs. triplet character of the two-hole state in the layered cuprates Bi2Sr2CaCu2O8+delta La2-xSrxCuO4 and Sr2CuO2Cl2. The combination of the photon circular polarization with the photoelectron spin detection gives access to the character of the photoemission final states, which correspond to the two-hole configurations localized at a (CuO4) site. In particular, the lowest energy state is found to have a very high singlet character in all the measured compounds. This can be considered as a strong indication of the existence and stability of the so-called Zhang-Rice singlets in the layered cuprates.
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| 8. |
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| 9. |
- Mizokawa, T., et al.
(författare)
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Spin-orbit coupling in the Mott insulator Ca2RuO4
- 2001
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 8707:7
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Tidskriftsartikel (refereegranskat)abstract
- O 1s x-ray absorption study of the Mott insulator Ca2RuO4 shows that the orbital population of the 4d t(2g) band dramatically changes with temperature. In addition, spin-resolved circularly polarized photoemission study of Ca2RuO4 shows that a substantial orbital angular momentum is induced in the Ru 4d t(2g) band. Based on the experimental results and model Hartree-Fock calculations, we argue that the cooperation between the strong spin-orbit coupling in the Ru 4d t(2g) band and the small distortion of the RuO6 octahedra causes the interesting changeover of the spin and orbital anisotropy as a function of temperature.
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| 10. |
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| 11. |
- Tjernberg, Oscar, et al.
(författare)
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Electrons, holes, and spin in Nd2-xCexCuO4-delta
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:10
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Tidskriftsartikel (refereegranskat)abstract
- The spin nature of the states at the top of the valence band in Nd2CuO4 and Nd1.85Ce0.15CuO4-delta has been investigated with spin polarized resonant photoemission. A clear Zhang-Rice singlet state is observed at the top of the valence band in the undoped compound showing that the parent compound of this electron doped superconductor is similar to the parent compounds of hole doped cuprate superconductors. Upon doping, the stability of the singlet is destroyed and the optimum doped compound Nd1.85Ce0.15CuO4-delta does not display any well-separated singlet state. These results indicate that hole contribution to the superconductivity in this system is not important in contrast to what has previously been suggested on the bases of transport measurements.
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| 12. |
- Braicovich, Lucio, et al.
(författare)
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Determining the electron-phonon coupling in superconducting cuprates by resonant inelastic x-ray scattering: Methods and results on Nd1+xBa2-xCu3O7-δ
- 2020
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Ingår i: Physical Review Research. - 2643-1564. ; 2:2
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Tidskriftsartikel (refereegranskat)abstract
- The coupling between lattice vibration quanta and valence electrons can induce charge-density modulations and decisively influence the transport properties of materials, e.g., leading to conventional superconductivity. In high-critical-temperature superconductors, where electronic correlation is the main actor, the actual role of electron-phonon coupling (EPC) is being intensely debated theoretically and investigated experimentally. We present an in-depth study of how the EPC strength can be obtained directly from resonant inelastic x-ray scattering (RIXS) data through the theoretical approach derived by Ament et al. [Europhys. Lett. 95, 27008 (2011)]. The role of the model parameters (e.g., phonon energy ω0, intermediate state lifetime 1/Γ, EPC matrix element M, and detuning energy Ω) is thoroughly analyzed, providing general relations among them that can be used to make quantitative estimates of the dimensionless EPC g=(M/ω0)2 without detailed microscopic modeling. We then apply these methods to very high-resolution Cu L3-edge RIXS spectra of three Nd1+xBa2−xCu3O7−δ films. For the insulating antiferromagnetic parent compound, the value of M as a function of the in-plane momentum transfer is obtained for Cu-O bond-stretching (breathing) and bond-bending (buckling) phonon branches. For the underdoped and the nearly optimally doped samples, the effects of Coulomb screening and of charge-density-wave correlations on M are assessed. In light of the anticipated further improvements of the RIXS experimental resolution, this work provides a solid framework for an exhaustive investigation of the EPC in cuprates and other quantum materials.
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| 13. |
- Brookes, N. B., et al.
(författare)
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Detection of Zhang-Rice singlets using spin-polarized photoemission
- 2001
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 8723:23
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Tidskriftsartikel (refereegranskat)abstract
- From a spin-resolved photoemission study on the Bi2Sr2CaCu2O8+delta superconductor, we show experimentally that the first ionization state is of nearly pure singlet character. This is true both above and below the superconducting transition and in the presence of doping and band formation. This provides direct support for the existence and stability of Zhang-Rice singlets in high-temperature superconductors, justifying the ansatz of single-band models. Moreover, we establish this technique as an important probe for a wide range of cuprates and strongly correlated materials.
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| 14. |
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| 15. |
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| 16. |
- Finazzi, M., et al.
(författare)
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Multiatomic resonant photoemission spectroscopy on CuO and NiO : Observation of antiresonant behavior
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 62:24, s. R16215-R16218
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Tidskriftsartikel (refereegranskat)abstract
- The intensity of the O 1s core photoemission peak has been measured for CuO and NiO as the photon energy is scanned across the L-3 absorption edge of the metal ion. In CuO, the O 1s peak shows a typical antiresonant behavior, with a sizable decrease of its cross section at photon energies below the Cu L-3 threshold. No detectable effect is observed for NiO. The CuO data are well reproduced by a multiatom resonant photoemission model based on resonant light scattering.
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| 17. |
- Finazzi, M., et al.
(författare)
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Photon energy dependence of the perpendicular geometry magnetic circular dichroism in the 2p3p3p resonant photoemission from Ni
- 2000
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 12:9, s. 2123-2133
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic circular dichroism in the perpendicular geometry of the resonant 2p3p3p photoemission (PE) spectroscopy has been investigated in metallic Ni as a function of the photon energy across the Ni Lj absorption edge. Within the experimental error bars, the photon energy dependence of the PE dichroism signal is the same as the one shown by the magnetic circular dichroism of the corresponding x-ray absorption (XMCD), obtained in the collinear geometry. This is attributed to the fact that, in metal Ni, the orbital [L-z] and dipolar [T-z] moments are smaller than the spin angular moment [S-z]. The latter is the dominating term in both the expressions that give the integrated values of the PE dichroism or XMCD intensities, Although the respective photon energy dependence is very similar, the normalized PE dichroism intensity is a factor similar to 5.6 smaller than the normalized XMCD signal, while only a factor similar to 1.6 is expected from theoretical considerations. This factor is observed even below the L-3 threshold, thus we exclude that the small intensity of the perpendicular geometry dichroism in the Ni 2p3p3p resonant photoemission is due to fast relaxation processes in the intermediate state.
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| 18. |
- Finazzi, M., et al.
(författare)
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Radiationless Raman versus Anger behavior at the Cu L-3 resonance of CuO and Cu2O
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:7, s. 4629-4635
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the behavior of the 2p3p3p and 2p3s3p Anger lines of CuO and Cu2O scanning the photon energy across the Cu L-3 resonance. For both samples, when the excitation energy is below the L-3 resonance, we observe the 2p3p3p and 2p3s3p peaks at constant binding energy. This behavior is typical of nonradiative resonant Raman scattering. If the photon energy is raised above the L-3 maximum, the two samples behave in different ways. In CuO, the Auger peaks are always observed at constant binding energy, while in Cu2O their kinetic energy first reaches a maximum at correspondence with the absorption threshold, and then stabilizes at a value slightly higher than the off-resonance Auger peaks. These differences are interpreted in terms of the different electronic structure of the Auger intermediate state at resonance. In CuO, the intermediate state corresponds to a single 2p(3/2) core hole, with the Cu 3d band completely filled. On the contrary, in Cu2O the intermediate state is represented by the combination of a 2p(3/2) hole with a 4sp electron in strong interaction with the O-2sp valence band. In CuO, for photon energies higher than 1.5 eV above the L-3-edge maximum, the constant binding energy radiationless Raman peaks are accompanied by constant kinetic energy replicas. These are attributed to the relaxation of the Auger intermediate state through electron-hole pair generation across the band gap of the material. Satellites that could be associated to relaxation precesses involving energies smaller than the band gap are not resolved. No variation of the lineshape of the Anger peaks is observed as a function of the sample temperature, indicating that different densities of thermally accessible excitations do not have a strong influence on the recombination process of the core hole.
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| 19. |
- Fumagalli, R., et al.
(författare)
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Mobile orbitons in Ca2CuO3: Crucial role of Hund's exchange
- 2020
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 101:20
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the CuL3 edge resonant inelastic x-ray scattering (RIXS) spectra of a quasi-1D antiferromagnet Ca2CuO3. In addition to the magnetic excitations, which are well-described by the two-spinon continuum, we observe two dispersive orbital excitations, the 3d(xy) and the 3d(yz) orbitons. We carry out a quantitative comparison of the RIXS spectra, obtained with two distinct incident polarizations, with a theoretical model. We show that any realistic spin-orbital model needs to include a finite, but realistic, Hund's exchange J(H) approximate to 0.5 eV. Its main effect is an increase in orbiton velocities, so that their theoretically calculated values match those observed experimentally. Even though Hund's exchange also mediates some interaction between spinon and orbiton, the picture of spin-orbit separation remains intact and describes orbiton motion in this compound.
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| 20. |
- Ghiringhelli, G., et al.
(författare)
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3d spin-orbit photoemission spectrum of nonferromagnetic materials : The test cases of CoO and Cu
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:7
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Tidskriftsartikel (refereegranskat)abstract
- The x-ray photoemission spectrum of the valence states of 3d transition-metal systems is spin polarized when using circularly polarized photons. The integral of the spin-orbit spectrum is proportional to the expectation value of the angular part of the 3d spin-orbit operator in the initial state. We show that this quantity can be used to get an estimate of the atomic orbital moment. While the measurement is sensitive to the magnetization axis, it does not require a net macroscopic magnetization nor the presence of a long-range magnetic order, and is therefore suitable for any transition-metal systems being antiferromagnetic or paramagnetic or magnetically disordered. In the case of full 3d shell the integral of the spin-orbit spectrum is zero, but the spectral shape can give a direct estimate of the 3d spin-orbit energy splitting DeltaE(SO). We have used Cu and CoO to experimentally test this technique. As expected Cu provides a vanishing result for , whereas for Co2+ in CoO we find =1.36h at 0 K. On the other hand we find DeltaE(SO)similar or equal to280 meV for Cu.
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| 21. |
- Krieger, G., et al.
(författare)
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Charge and Spin Order Dichotomy in NdNiO2 Driven by the Capping Layer
- 2022
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 129:2
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Tidskriftsartikel (refereegranskat)abstract
- Superconductivity in infinite-layer nickelates holds exciting analogies with that of cuprates, with similar structures and 3d-electron count. Using resonant inelastic x-ray scattering, we studied electronic and magnetic excitations and charge density correlations in Nd1-xSrxNiO2 thin films with and without an SrTiO3 capping layer. We observe dispersing magnons only in the capped samples, progressively dampened at higher doping. We detect an elastic resonant scattering peak in the uncapped x=0 compound at wave vector (∼⅓,0), remindful of the charge order signal in hole doped cuprates. The peak weakens at x=0.05 and disappears in the superconducting x=0.20 film. The role of the capping on the electronic reconstruction far from the interface remains to be understood.
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| 22. |
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| 23. |
- Martinelli, L., et al.
(författare)
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Collective Nature of Orbital Excitations in Layered Cuprates in the Absence of Apical Oxygens
- 2024
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 132:6
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the 3d orbital excitations in CaCuO2 (CCO), Nd2CuO4 (NCO), and La2CuO4 (LCO) using high-resolution resonant inelastic x-ray scattering. In LCO they behave as well-localized excitations, similarly to several other cuprates. On the contrary, in CCO and NCO the dxy orbital clearly disperses, pointing to a collective character of this excitation (orbiton) in compounds without apical oxygen. We ascribe the origin of the dispersion as stemming from a substantial next-nearest-neighbor (NNN) orbital superexchange. Such an exchange leads to the liberation of the orbiton from its coupling to magnons, which is associated with the orbiton hopping between nearest neighbor copper sites. Finally, we show that the exceptionally large NNN orbital superexchange can be traced back to the absence of apical oxygens suppressing the charge transfer energy.
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| 24. |
- Minar, J., et al.
(författare)
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Theoretical description of the Fano-effect in the angle-integrated valence-band photoemission of paramagnetic solids
- 2001
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 73:6, s. 663-666
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical description of the Fano-effect in the angle-integrated valence-band photoemission (VB XPS) of paramagnetic solids is presented that is based on the one-step model of photoemission and relativistic multiple scattering theory. Applications to fcc-Cu and fcc-Ag led to a very satisfying agreement with recent experimental data that show the Fano-effect, i.e., a finite spin polarisation of the photoelectrons is found for excitation with circularly polarised radiation. As can be demonstrated by model calculations, this finding is caused by the presence of spin-orbit coupling. To allow for a more detailed discussion of the spectra, a simplified description of the Fano-effect is presented that treats spin-orbit coupling as a perturbation.
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| 25. |
- Minar, J., et al.
(författare)
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Theoretical description of the Fano effect in the angle-integrated valence-band photoemission of paramagnetic solids
- 2001
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 6314:14
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical description of the Fano effect in the angle-integrated valence-band photoemission of paramagnetic solids is presented that is based on the one-step model of photoemission and relativistic multiple-scattering theory. Applications to fcc-Cu led to a very satisfying agreement with recent experimental data that show the Fano effect, i.e., a finite spin-polarization for the spectra is found for excitation with circularly polarized radiation. As can be demonstrated by model calculations. this finding is caused by the presence of spin-orbit coupling. To allow for a more detailed discussion of the spectra a simplified description of the Fano effect is presented that treats spin-orbit coupling as a perturbation.
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