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Instruments / Technical Area	Publication Details	Published
	Spin fluctuations associated with the collapse of the pseudogap in a cuprate superconductor M. Zhu , D. J. Voneshen , S. Raymond , O. J. Lipscombe , C. C. Tam , S. M. Hayden Nature Physics 19, 99 - 105 DOI: 10.1038/s41567-022-01825-3 Show Abstract ▼ Abstract: Theories of the origin of superconductivity in cuprates depend on an understanding of their normal state, which exhibits various competing orders. Transport and thermodynamic measurements on La2 − xSrxCuO4 show signatures of a quantum critical point and the associated fluctuations, including a peak in the electronic specific heat versus doping, near the doping p* where the pseudogap collapses. The fundamental nature of these quantum fluctuations is unclear. Here we use inelastic neutron scattering to show that, close to the superconducting critical temperature and near p, there are very-low-energy collective spin excitations with characteristic energies of ~5 meV. Cooling and applying a magnetic field creates a mixed state with a stronger magnetic response below 10 meV. We conclude that the low-energy spin fluctuations are due to the collapse of the pseudogap combined with an underlying tendency to magnetic order. We show that the large specific heat near p can be understood in terms of collective spin fluctuations. The spin fluctuations we measure exist across the superconducting phase diagram and may be related to the strange metal behaviour observed in overdoped cuprates.	Jan 2023
I19-Small Molecule Single Crystal Diffraction	Pronounced interplay between intrinsic phase-coexistence and octahedral tilt magnitude in hole-doped lanthanum cuprates Jeremiah P. Tidey , En-Pei Liu , Yen-Chung Lai , Yu-Chun Chuang , Wei-Tin Chen , Lauren J. Cane , Chris Lester , Alexander N. D. Petsch , Anna Herlihy , Arkadiy Simonov , Stephen M. Hayden , Mark Senn Scientific Reports 12 DOI: 10.1038/s41598-022-18574-1 Diamond Proposal Number(s): [27647] Open Access Show Abstract ▼ Abstract: Definitive understanding of superconductivity and its interplay with structural symmetry in the hole-doped lanthanum cuprates remains elusive. The suppression of superconductivity around 1/8th doping maintains particular focus, often attributed to charge-density waves (CDWs) ordering in the low-temperature tetragonal (LTT) phase. Central to many investigations into this interplay is the thesis that La1.875Ba0.125CuO4 and particularly La1.675Eu0.2Sr0.125CuO4 present model systems of purely LTT structure at low temperature. However, combining single-crystal and high-resolution powder X-ray diffraction, we find these to exhibit significant, intrinsic coexistence of LTT and low-temperature orthorhombic domains, typically associated with superconductivity, even at 10 K. Our two-phase models reveal substantially greater tilting of CuO6 octahedra in the LTT phase, markedly buckling the CuO2 planes. This would couple significantly to band narrowing, potentially indicating a picture of electronically driven phase segregation, reminiscent of optimally doped manganites. These results call for reassessment of many experiments seeking to elucidate structural and electronic interplay at 1/8 doping.	Aug 2022
	Charge density waves and Fermi surface reconstruction in the clean overdoped cuprate superconductor Tl2Ba2CuO6+δ C. C. Tam , M. Zhu , J. Ayres , K. Kummer , F. Yakhou-Harris , J. R. Cooper , A. Carrington , S. M. Hayden Nature Communications 13 DOI: 10.1038/s41467-022-28124-y Open Access Show Abstract ▼ Abstract: Hall effect and quantum oscillation measurements on high temperature cuprate superconductors show that underdoped compositions have small Fermi surface pockets whereas when heavily overdoped, a single much larger pocket is found. The origin of this change in electronic structure has been unclear, but may be related to the high temperature superconductivity. Here we show that the clean overdoped single-layer cuprate Tl2Ba2CuO6+δ (Tl2201) displays CDW order with a remarkably long correlation length ξ ≈ 200 Å which disappears above a hole doping of pCDW ≈ 0.265. We show that the evolution of the electronic properties of Tl2201 as the doping is lowered may be explained by a Fermi surface reconstruction which accompanies the emergence of the CDW below pCDW. Our results demonstrate importance of CDW correlations in understanding the electronic properties of overdoped cuprates.	Jan 2022
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 La2-x Srx CuO4 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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