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Instruments / Technical Area	Publication Details	Published
I21-Resonant Inelastic X-ray Scattering (RIXS)	Evolution of spin excitations from bulk to monolayer FeSe Jonathan Pelliciari , Seher Karakuzu , Qi Song , Riccardo Arpaia , Abhishek Nag , Matteo Rossi , Jiemin Li , Tianlun Yu , Xiaoyang Chen , Rui Peng , Mirian Garcia-Fernandez , Andrew C. Walters , Qisi Wang , Jun Zhao , Giacomo Ghiringhelli , Donglai Feng , Thomas A. Maier , Ke-Jin Zhou , Steven Johnston , Riccardo Comin Nature Communications 12 DOI: 10.1038/s41467-021-23317-3 Diamond Proposal Number(s): [18883] Open Access Show Abstract ▼ Abstract: In ultrathin films of FeSe grown on SrTiO3 (FeSe/STO), the superconducting transition temperature Tc is increased by almost an order of magnitude, raising questions on the pairing mechanism. As in other superconductors, antiferromagnetic spin fluctuations have been proposed to mediate SC making it essential to study the evolution of the spin dynamics of FeSe from the bulk to the ultrathin limit. Here, we investigate the spin excitations in bulk and monolayer FeSe/STO using resonant inelastic x-ray scattering (RIXS) and quantum Monte Carlo (QMC) calculations. Despite the absence of long-range magnetic order, bulk FeSe displays dispersive magnetic excitations reminiscent of other Fe-pnictides. Conversely, the spin excitations in FeSe/STO are gapped, dispersionless, and significantly hardened relative to its bulk counterpart. By comparing our RIXS results with simulations of a bilayer Hubbard model, we connect the evolution of the spin excitations to the Fermiology of the two systems revealing a remarkable reconfiguration of spin excitations in FeSe/STO, essential to understand the role of spin fluctuations in the pairing mechanism.	May 2021
I21-Resonant Inelastic X-ray Scattering (RIXS)	Strong superexchange in a d9−δ nickelate revealed by resonant inelastic X-ray scattering J. Q. Lin , P. Villar Arribi , G. Fabbris , A. s. Botana , D. Meyers , H. Miao , Y. Shen , D. G. Mazzone , J. Feng , G. S. Chiuzbaian , A. Nag , A. C. Walters , M. Garcia-Fernandez , K.-J. Zhou , J. Pelliciari , I. Jarrige , J. W. Freeland , J. Zhang , J. F. Mitchell , V. Bisogni , X. Liu , M. R. Norman , M. P. M. Dean Physical Review Letters 126 DOI: 10.1103/PhysRevLett.126.087001 Diamond Proposal Number(s): [18519] Show Abstract ▼ Abstract: The discovery of superconductivity in a d 9 − δ nickelate has inspired disparate theoretical perspectives regarding the essential physics of this class of materials. A key issue is the magnitude of the magnetic superexchange, which relates to whether cuprate-like high-temperature nickelate superconductivity could be realized. We address this question using Ni L -edge and O K -edge spectroscopy of the reduced d 9 − 1 / 3 trilayer nickelates R 4 Ni 3 O 8 (where R = La , Pr) and associated theoretical modeling. A magnon energy scale of ∼ 80 meV resulting from a nearest-neighbor magnetic exchange of J = 69 ( 4 ) meV is observed, proving that d 9 − δ nickelates can host a large superexchange. This value, along with that of the Ni-O hybridization estimated from our O K -edge data, implies that trilayer nickelates represent an intermediate case between the infinite-layer nickelates and the cuprates. Layered nickelates thus provide a route to testing the relevance of superexchange to nickelate superconductivity.	Feb 2021
I21-Resonant Inelastic X-ray Scattering (RIXS)	Multiorbital charge-density wave excitations and concomitant phonon anomalies in Bi2Sr2LaCuO6+δ Jiemin Li , Abhishek Nag , Jonathan Pelliciari , Hannah Robarts , Andrew Walters , Mirian Garcia-Fernandez , Hiroshi Eisaki , Dongjoon Song , Hong Ding , Steven Johnston , Riccardo Comin , Ke-Jin Zhou Proceedings Of The National Academy Of Sciences 89 DOI: 10.1073/pnas.2001755117 Diamond Proposal Number(s): [19886, 21184, 21277] Open Access Show Abstract ▼ Abstract: Charge-density waves (CDWs) are ubiquitous in underdoped cuprate superconductors. As a modulation of the valence electron density, CDWs in hole-doped cuprates possess both Cu-3d and O-2p orbital character owing to the strong hybridization of these orbitals near the Fermi level. Here, we investigate underdoped Bi2Sr1.4La0.6CuO6+δ using resonant inelastic X-ray scattering (RIXS) and find that a short-range CDW exists at both Cu and O sublattices in the copper-oxide (CuO2) planes with a comparable periodicity and correlation length. Furthermore, we uncover bond-stretching and bond-buckling phonon anomalies concomitant to the CDWs. Comparing to slightly overdoped Bi2Sr1.8La0.2CuO6+δ, where neither CDWs nor phonon anomalies appear, we highlight that a sharp intensity anomaly is induced in the proximity of the CDW wavevector (QCDW) for the bond-buckling phonon, in concert with the diffused intensity enhancement of the bond-stretching phonon at wavevectors much greater than QCDW. Our results provide a comprehensive picture of the quasistatic CDWs, their dispersive excitations, and associated electron-phonon anomalies, which are key for understanding the competing electronic instabilities in cuprates.	Jun 2020
I21-Resonant Inelastic X-ray Scattering (RIXS)	Strongly correlated charge density wave in La2−xSrxCuO4 evidenced by doping-dependent phonon anomaly J. Q. Lin , H. Miao , D. G. Mazzone , G. d. Gu , A. Nag , A. C. Walters , M. Garcia-Fernandez , A. Barbour , J. Pelliciari , I. Jarrige , M. Oda , K. Kurosawa , N. Momono , K. Zhou , V. Bisogni , X. Liu , M. P. M. Dean Physical Review Letters 124 DOI: 10.1103/PhysRevLett.124.207005 Diamond Proposal Number(s): [22261] Show Abstract ▼ Abstract: The discovery of charge-density-wave-related effects in the resonant inelastic x-ray scattering spectra of cuprates holds the tantalizing promise of clarifying the interactions that stabilize the electronic order. Here, we report a comprehensive resonant inelastic x-ray scattering study of La 2 − x Sr x CuO 4 finding that charge-density wave effects persist up to a remarkably high doping level of x = 0.21 before disappearing at x = 0.25 . The inelastic excitation spectra remain essentially unchanged with doping despite crossing a topological transition in the Fermi surface. This indicates that the spectra contain little or no direct coupling to electronic excitations near the Fermi surface, rather they are dominated by the resonant cross section for phonons and charge-density-wave-induced phonon softening. We interpret our results in terms of a charge-density wave that is generated by strong correlations and a phonon response that is driven by the charge-density-wave-induced modification of the lattice.	May 2020
	Doping dependence of the magnetic excitations in La2−x Srx CuO4 D. Meyers , H. Miao , A. Walters , V. Bisogni , R. S. Springell , M. D'Astuto , M. Dantz , J. Pelliciari , H. Y. Huang , J. Okamoto , D. J. Huang , J. P. Hill , X. He , I. Božović , T. Schmitt , M. P. M. Dean Physical Review B 95 DOI: 10.1103/PhysRevB.95.075139 Show Abstract ▼ Abstract: The magnetic correlations within the cuprates have undergone intense scrutiny as part of efforts to understand high-temperature superconductivity. We explore the evolution of the magnetic correlations along the nodal direction of the Brillouin zone in La 2 − x Sr x CuO 4 , spanning the doping phase diagram from the antiferromagnetic Mott insulator at x = 0 to the metallic phase at x = 0.26 . Magnetic excitations along this direction are found to be systematically softened and broadened with doping, at a higher rate than the excitations along the antinodal direction. This phenomenology is discussed in terms of the nature of the magnetism in the doped cuprates. Survival of the high-energy magnetic excitations, even in the overdoped regime, indicates that these excitations are marginal to pairing, while the influence of the low-energy excitations remains ambiguous.	Feb 2017

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