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Instruments / Technical Area	Publication Details	Published
I21-Resonant Inelastic X-ray Scattering (RIXS)	Many-body physics of single and double spin-flip excitations in NiO A. Nag , H. C. Robarts , F. Wenzel , J. Li , H. Elnaggar , R.-p. Wang , A. Walters , M. Garcia-fernandez , F. M. F. De Groot , M. W. Haverkort , K. Zhou Physical Review Letters 124 DOI: 10.1103/PhysRevLett.124.067202 Open Access Show Abstract ▼ Abstract: Understanding many-body physics of elementary excitations has advanced our control over material properties. Here, we study spin-flip excitations in NiO using Ni L3-edge resonant inelastic x-ray scattering (RIXS) and present a strikingly different resonant energy behavior between single and double spin-flip excitations. Comparing our results with single-site full-multiplet ligand field theory calculations we find that the spectral weight of the double-magnon excitations originates primarily from the double spin-flip transition of the quadrupolar RIXS process within a single magnetic site. Quadrupolar spin-flip processes are among the least studied excitations, despite being important for multiferroic or spin-nematic materials due to their difficult detection. We identify intermediate state multiplets and intra-atomic core-valence exchange interactions as the key many-body factors determining the fate of such excitations. RIXS resonant energy dependence can act as a convincing proof of existence of nondipolar higher-ranked magnetic orders in systems for which, only theoretical predictions are available.	Feb 2020
I21-Resonant Inelastic X-ray Scattering (RIXS)	Electronic structure of the parent compound of superconducting infinite-layer nickelates M. Hepting , D. Li , C. J. Jia , H. Lu , E. Paris , Y. Tseng , X. Feng , M. Osada , E. Been , Y. Hikita , Y.-d. Chuang , Z. Hussain , K. J. Zhou , A. Nag , M. Garcia-fernandez , M. Rossi , H. Y. Huang , D. J. Huang , Z. X. Shen , T. Schmitt , H. Y. Hwang , B. Moritz , J. Zaanen , T. P. Devereaux , W. S. Lee Nature Materials 59 DOI: 10.1038/s41563-019-0585-z Diamond Proposal Number(s): [22009] Show Abstract ▼ Abstract: The search continues for nickel oxide-based materials with electronic properties similar to cuprate high-temperature superconductors. The recent discovery of superconductivity in the doped infinite-layer nickelate NdNiO2 has strengthened these efforts. Here, we use X-ray spectroscopy and density functional theory to show that the electronic structure of LaNiO2 and NdNiO2, while similar to the cuprates, includes significant distinctions. Unlike cuprates, the rare-earth spacer layer in the infinite-layer nickelate supports a weakly interacting three-dimensional 5d metallic state, which hybridizes with a quasi-two-dimensional, strongly correlated state with 3 d x 2 − y 2 3dx2−y2 symmetry in the NiO2 layers. Thus, the infinite-layer nickelate can be regarded as a sibling of the rare-earth intermetallics, which are well known for heavy fermion behaviour, where the NiO2 correlated layers play an analogous role to the 4f states in rare-earth heavy fermion compounds. This Kondo- or Anderson-lattice-like ‘oxide-intermetallic’ replaces the Mott insulator as the reference state from which superconductivity emerges upon doping.	Jan 2020
I21-Resonant Inelastic X-ray Scattering (RIXS)	Doping evolution of the charge excitations and electron correlations in electron-doped superconducting La2−xCexCuO4 Jiaqi Lin , Jie Yuan , Kui Jin , Zhiping Yin , Gang Li , Kejin Zhou , Xingye Lu , Marcus Dantz , Thorsten Schmitt , Hong Ding , Haizhong Guo , Mark P. M. Dean , Xuerong Liu Npj Quantum Materials 5 DOI: 10.1038/s41535-019-0205-9 Open Access Show Abstract ▼ Abstract: Electron correlations play a dominant role in the charge dynamics of the cuprates. We use resonant inelastic X-ray scattering (RIXS) to track the doping dependence of the collective charge excitations in electron doped La 2−x 2−x Ce x x CuO 4 4 (LCCO). From the resonant energy dependence and the out-of-plane momentum dependence, the charge excitations are identified as three-dimensional (3D) plasmons, which reflect the nature of the electronic structure and Coulomb repulsion on both short and long lengthscales. With increasing electron doping, the plasmon excitations increase monotonically in energy, a consequence of the electron correlation effect on electron structure near the Fermi surface (FS). Importantly, the plasmon excitations evolve from a broad feature into a well-defined peak with much increased life time, revealing the evolution of the electrons from incoherent states to coherent quasi-particles near the FS. Such evolution marks the reduction of the short-range electronic correlation, and thus the softening of the Mottness of the system with increasing electron doping.	Jan 2020
I21-Resonant Inelastic X-ray Scattering (RIXS)	Superstructure control of first-cycle voltage hysteresis in O-redox cathodes Robert A. House , Urmimala Maitra , Miguel A. Pérez-osorio , Juan G. Lozano , Liyu Jin , James W. Somerville , Laurent C. Duda , Abhishek Nag , Andrew Walters , Kejin Zhou , Matthew R. Roberts , Peter G. Bruce Nature DOI: 10.1038/s41586-019-1854-3 Show Abstract ▼ Abstract: Alkali-rich transition metal oxide intercalation cathodes can increase the energy density of Li and Na-ion batteries by storing charge on the oxide and transition metal (TM) ions1–10. The high voltage associated with oxidation of O2- on the first charge is not recovered on discharge, resulting in significantly reduced energy density11. Displacement of TM ions from the TM to alkali metal layers has been proposed to explain the first cycle voltage loss9,12–16. By comparing two closely related intercalation cathodes, Na0.75[Li0.25Mn0.75]O2 and Na0.6[Li0.2Mn0.8]O2, we show that the first cycle voltage hysteresis is determined by the superstructure, specifically the local ordering of Li/TM ions in the TM layers. The honeycomb superstructure of Na0.75[Li0.25Mn0.75]O2, present in almost all O-redox compounds, is lost on charging, driven, in part, by formation of molecular O2 inside the solid. The O2 molecules are cleaved on discharge reforming O2-, but the Mn ions have migrated in the plane changing the coordination around O2- significantly lowering the voltage on discharge (hysteresis). The ribbon superstructure in Na0.6[Li0.2Mn0.8]O2 inhibits Mn disorder and hence O2 formation, suppressing hysteresis and promoting stable electron holes on O2- which are revealed by XAS. The results show that voltage hysteresis can be avoided in O-redox cathodes by forming materials with a superstructure (cation ordering) in the TM layers that suppresses TM migration.	Dec 2019
I21-Resonant Inelastic X-ray Scattering (RIXS)	Anisotropic damping and wave vector dependent susceptibility of the spin fluctuations in La 2 − x Sr x CuO 4 studied by resonant inelastic x-ray scattering H. C. Robarts , M. Barthelemy , K. Kummer , Mirian Garcia-fernandez , J. Li , A. Nag , A. C. Walters , K. Zhou , S. M. Hayden Physical Review B 100 DOI: 10.1103/PhysRevB.100.214510 Diamond Proposal Number(s): [18469, 18512] Show Abstract ▼ Abstract: We report high-resolution resonant inelastic x-ray scattering (RIXS) measurements of the collective spin fluctuations in three compositions of the superconducting cuprate system La 2 − x Sr x CuO 4 . We have mapped out the excitations throughout much of the two-dimensional ( h , k ) Brillouin zone. The spin fluctuations in La 2 − x Sr x CuO 4 are found to be fairly well described by a damped harmonic oscillator model, thus our data allows us to determine the full wave vector dependence of the damping parameter. This parameter increases with doping and is largest along the ( h , h ) line, where it is peaked near ( 0.2 , 0.2 ) . We have used a new procedure to determine the absolute wave vector dependent susceptibility for the doped compositions La 2 − x Sr x CuO 4 ( x = 0.12 , 0.16 ) by normalizing our data to La 2 CuO 4 measurements made with inelastic neutron scattering (INS). We find that the evolution with doping of the intensity of high-energy excitations measured by RIXS and INS is consistent. For the doped compositions, the wave vector dependent susceptibility is much larger at ( 1 4 , 1 4 ) than at ( 1 2 , 0 ) . It increases rapidly along the ( h , h ) line towards the antiferromagnetic wave vector of the parent compound ( 1 2 , 1 2 ) . Thus, the strongest magnetic excitations, and those predicted to favor superconductive pairing, occur towards the ( 1 2 , 1 2 ) position as observed by INS.	Dec 2019
I21-Resonant Inelastic X-ray Scattering (RIXS)	High-resolution resonant inelastic x-ray scattering study of the electron-phonon coupling in honeycomb α − Li 2IrO3 J. G. Vale , C. D. Dashwood , E. Paris , L. S. I. Veiga , Mirian Garcia-fernandez , A. Nag , A. Walters , K. Zhou , I.-m. Pietsch , Anton Jesche , P. Gegenwart , R. Coldea , T. Schmitt , D. F. Mcmorrow Physical Review B 100 DOI: 10.1103/PhysRevB.100.224303 Diamond Proposal Number(s): [20569] Show Abstract ▼ Abstract: The excitations in honeycomb α − Li 2 IrO 3 have been investigated with high-resolution resonant inelastic x-ray scattering (RIXS) at the O K edge. The low-energy response is dominated by a fully resolved ladder of excitations, which we interpret as being due to multiphonon processes in the presence of strong electron-phonon coupling (EPC). At higher energies, the orbital excitations are shown to be dressed by phonons. The high quality of the data permits a quantitative test of the analytical model for the RIXS cross section, which has been proposed to describe EPC in transition-metal oxides (TMOs). We find that the magnitude of the EPC is comparable to that found for a range of 3 d TMOs. This indicates that EPC may be of equal importance in determining the phenomenology displayed by corresponding 5 d -based systems.	Dec 2019
	Probing multi-spinon excitations outside of the two-spinon continuum in the antiferromagnetic spin chain cuprate Sr2CuO3 J. Schlappa , U. Kumar , K. J. Zhou , S. Singh , M. Mourigal , V. N. Strocov , A. Revcolevschi , L. Patthey , H. M. Ronnow , S. Johnston , T. Schmitt Nature Communications 9 DOI: 10.1038/s41467-018-07838-y Open Access Show Abstract ▼ Abstract: One-dimensional (1D) magnetic insulators have attracted significant interest as a platform for studying quasiparticle fractionalization, quantum criticality, and emergent phenomena. The spin-1/2 Heisenberg chain with antiferromagnetic nearest neighbour interactions is an important reference system; its elementary magnetic excitations are spin-1/2 quasiparticles called spinons that are created in even numbers. However, while the excitation continuum associated with two-spinon states is routinely observed, the study of four-spinon and higher multi-spinon states is an open area of research. Here we show that four-spinon excitations can be accessed directly in Sr2CuO3 using resonant inelastic x-ray scattering (RIXS) in a region of phase space clearly separated from the two-spinon continuum. Our finding is made possible by the fundamental differences in the correlation function probed by RIXS in comparison to other probes. This advance holds promise as a tool in the search for novel quantum states and quantum spin liquids.	Dec 2018
Mechanical Engineering	A new procurement strategy to challenge the supplier constraints created when using a fully developed reference design G. E. Howell , N. Baker , S. Davies , M. Garcia-fernandez , H. C. Huang , S. M. Scott , A. Walters , K. Zhou MEDSI2018 DOI: 10.18429/JACoW-MEDSI2018-THOPMA04 Open Access Show Abstract ▼ Abstract: A common procurement strategy is to produce a fully optimised reference design that makes assumptions about the manufacturing process and supplier capability. This approach can restrict the opportunities for some companies to include their own specialist manufacturing capability to provide a more effective and cost efficient solution. A new approach is suggested following the recent experience at Diamond Light Source. The manufacture of high stiffness welded fabrications up to 13m in length for the I21 RIXS Spectrometer is used as an example. The I21 RIXS Spectrometer design was optimised for stiffness and control of vibration. The use of Finite Element Analysis enabled different design options and compromises to be explored utilising the supplier's capabilities. The final design was tested during manufacture to verify the FEA model. With the I21 RIXS Spectrometer commissioned the data collected shows the final stability performance of the system including detector stability over full experiment durations has met the scientific goals of the design.	Dec 2018
	Orbital breathing effects in the computation of x-ray d -ion spectra in solids by ab initio wave-function-based methods Nikolay A. Bogdanov , Valentina Bisogni , Roberto Kraus , Claude Monney , Kejin Zhou , Thorsten Schmitt , Jochen Geck , Alexander O Mitrushchenkov , Hermann Stoll , Jeroen Van Den Brink , Liviu Hozoi Journal Of Physics: Condensed Matter 29 DOI: 10.1088/1361-648X/29/3/035502 Show Abstract ▼ Abstract: 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 Li2CuO2, 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.	Jan 2017
	Beamline I21 – Resonant Inelastic X-ray Scattering (RIXS) at Diamond Ke-jin Zhou 9th international conference on Inelastic X-ray Scattering Show Abstract ▼ Abstract: Resonant inelastic soft X-ray scattering (RIXS) [1, 2] is a powerful bulk-sensitive photon-in / photonout spectroscopic and scattering probe of the electronic structure of condensed matter with elemental sensitivity. It is a unique tool for studying low energy excitations in complex correlated systems, being sensitive to charge-, orbital-, spin-, and lattice-degrees of freedom [3-7]. Dedicated instrumentation for soft X-ray RIXS with ultra-high resolution in energy and momentum spaces has become available thereby enabling characterization of collective excitations such as magnons and phonons. In this presentation I will give a brief introduction of the I21-RIXS beamline which is currently under construction at Diamond Light Source in the UK. Details of the key beamline performance, the optical design and the mechanical designs are to be presented.	Nov 2015

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