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Instruments / Technical Area	Publication Details	Published
I21-Resonant Inelastic X-ray Scattering (RIXS)	Dynamical spin susceptibility in La2CuO4 studied by resonant inelastic x-ray scattering H. C. Robarts , M. Garcia-Fernandez , J. Li , A. Nag , A. C. Walters , N. E. Headings , S. M. Hayden , K.-J. Zhou Physical Review B 103 DOI: 10.1103/PhysRevB.103.224427 Diamond Proposal Number(s): [18469] Open Access Show Abstract ▼ Abstract: Resonant inelastic x-ray scattering (RIXS) is a powerful probe of elementary excitations in solids. It is now widely applied to study magnetic excitations. However, its complex cross section means that RIXS has been more difficult to interpret than inelastic neutron scattering (INS). Here we report ∼ 37 meV resolution RIXS measurements of the magnetic excitations in La 2 CuO 4 , the antiferromagnetic parent of one system of high-temperature superconductors. At high energies ( ∼ 2 eV), the RIXS spectra show angular-dependent d d orbital excitations in agreement with previous RIXS studies but show new structure. They are interpreted with single-site multiplet calculations. At low energies ( ≲ 0.3 eV), we model the wave-vector-dependent single magnon RIXS intensity as the product of the calculated single-ion spin-flip RIXS cross section and the dynamical structure factor S ( Q , ω ) of the spin-wave excitations. When S ( Q , ω ) is extracted from our data, the wave-vector-dependence of the single-magnon pole intensity shows a similar variation to that observed by INS. Our results confirm that suitably corrected RIXS data can yield the genuine wave-vector and energy dependence of S ( Q , ω ) for a cuprate antiferromagnet. In addition to spin waves, our data show structured multimagnon excitations with dispersing peaks in the intensity at energies higher than the single-magnon excitations.	Jun 2021
I21-Resonant Inelastic X-ray Scattering (RIXS)	Detection of acoustic plasmons in hole-doped lanthanum and bismuth cuprate superconductors using resonant inelastic X-ray scattering A. Nag , M. Zhu , M. Bejas , J. Li , H. C. Robarts , H. Yamase , A. N. Petsch , D. Song , H. Eisaki , A. C. Walters , M. Garcia-Fernandez , A. Greco , S. M. Hayden , K. Zhou Physical Review Letters 125 DOI: 10.1103/PhysRevLett.125.257002 Diamond Proposal Number(s): [24587] Open Access Show Abstract ▼ Abstract: High T c superconductors show a rich variety of phases associated with their charge degrees of freedom. Valence charges can give rise to charge ordering or acoustic plasmons in these layered cuprate superconductors. While charge ordering has been observed for both hole- and electron-doped cuprates, acoustic plasmons have only been found in electron-doped materials. Here, we use resonant inelastic x-ray scattering to observe the presence of acoustic plasmons in two families of hole-doped cuprate superconductors ( La 1.84 Sr 0.16 CuO 4 and Bi 2 Sr 1.6 La 0.4 CuO 6 + δ ), crucially completing the picture. Interestingly, in contrast to the quasistatic charge ordering which manifests at both Cu and O sites, the observed acoustic plasmons are predominantly associated with the O sites, revealing a unique dichotomy in the behavior of valence charges in hole-doped cuprates.	Dec 2020
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
I05-ARPES	Direct observation of orbital hybridisation in a cuprate superconductor C. E. Matt , D. Sutter , A. M. Cook , Y. Sassa , Martin Mansson , O. Tjernberg , L. Das , M. Horio , D. Destraz , C. G. Fatuzzo , K. Hauser , M. Shi , M. Kobayashi , V. N. Strocov , T. Schmitt , P. Dudin , M. Hoesch , S. Pyon , T. Takayama , H. Takagi , O. J. Lipscombe , S. M. Hayden , T. Kurosawa , N. Momono , M. Oda , T. Neupert , J. Chang Nature Communications 9 DOI: 10.1038/s41467-018-03266-0 Diamond Proposal Number(s): [10550] Open Access Show Abstract ▼ Abstract: The minimal ingredients to explain the essential physics of layered copper-oxide (cuprates) materials remains heavily debated. Effective low-energy single-band models of the copper–oxygen orbitals are widely used because there exists no strong experimental evidence supporting multi-band structures. Here, we report angle-resolved photoelectron spectroscopy experiments on La-based cuprates that provide direct observation of a two-band structure. This electronic structure, qualitatively consistent with density functional theory, is parametrised by a two-orbital (d x 2 −y 2 dx2-y2 and d z 2 dz2 ) tight-binding model. We quantify the orbital hybridisation which provides an explanation for the Fermi surface topology and the proximity of the van-Hove singularity to the Fermi level. Our analysis leads to a unification of electronic hopping parameters for single-layer cuprates and we conclude that hybridisation, restraining d-wave pairing, is an important optimisation element for superconductivity.	Mar 2018
I16-Materials and Magnetism	Charge density wave fluctuations in La2-xSrxCuO4 and their competition with superconductivity Tom Croft , Christopher Lester , Mark Senn , Alessandro Bombardi , Stephen Hayden Physical Review B 89 (22) DOI: 10.1103/PhysRevB.89.224513 Show Abstract ▼ Abstract: We report hard (14 keV) x-ray diffraction measurements on three compositions (x=0.11,0.12,0.13) of the high-temperature superconductor La2-xSrxCuO4. All samples show charge-density-wave (CDW) order with onset temperatures in the range 51-80 K and ordering wavevectors close to (0.23,0,0.5). The CDW is strongest with the longest in-plane correlation length near 1/8 doping. On entering the superconducting state the CDW is suppressed, demonstrating the strong competition between the charge order and superconductivity. CDW order coexists with incommensurate magnetic order and wavevectors of the two modulations have the simple relationship $\delta_{charge}= 2\delta_{spin}$. The intensity of the CDW Bragg peak tracks the intensity of the low-energy (quasi-elastic) spin fluctuations. We present a phase diagram of La2-xSrxCuO4 including the pseudogap phase, CDW and magnetic order.	Jun 2014

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