| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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