Author: Martin Maxmilian Passer Bluschke
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Martin Bluschke
Publisher: Springer Nature
ISBN: 3030479021
Category : Science
Languages : en
Pages : 170

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In this thesis chemical and epitaxial degrees of freedom are used to manipulate charge and spin ordering phenomena in two families of transition metal oxides, while taking advantage of state-of-the-art resonant x-ray scattering (RXS) methods to characterize their microscopic origin in a comprehensive manner. First, the relationship of charge density wave order to both magnetism and the "pseudogap" phenomenon is systematically examined as a function of charge-carrier doping and isovalent chemical substitution in single crystals of a copper oxide high-temperature superconductor. Then, in copper oxide thin films, an unusual three-dimensionally long-range-ordered charge density wave state is discovered, which persists to much higher temperatures than charge-ordered states in other high-temperature superconductors. By combining crystallographic and spectroscopic measurements, the origin of this phenomenon is traced to the epitaxial relationship with the underlying substrate. This discovery opens new perspectives for the investigation of charge order and its influence on the electronic properties of the cuprates. In a separate set of RXS experiments on superlattices with alternating nickel and dysprosium oxides, several temperature- and magnetic-field-induced magnetic phase transitions are discovered. These observations are explained in a model based on transfer of magnetic order and magneto-crystalline anisotropy between the Ni and Dy subsystems, thus establishing a novel model system for the interplay between transition-metal and rare-earth magnetism.

Author: Min Gu Kang (S.M.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 104

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After 30 years of extensive scrutiny from their discovery in 1986, copper oxide high-temperature superconductors remain one of the most enigmatic and captivating platforms for emergent many-body phases in condensed matter physics. Understanding the emergent physics of collective electronic orders and excitations across the cuprate phase diagram is a key to decode the puzzle of high-temperature superconductivity and how it arises from the strongly correlated Mott state. With the advance of soft X-ray instrumentations during the last decade, resonant elastic and inelastic X-ray scattering (REXS and RIXS) have rapidly established as highly sensitive and versatile probes of electronic orders and excitations in quantum materials. Using REXS at the Cu-L3 resonance, we investigated the evolution of momentum-space topology of charge correlation in electron-doped cuprates T'-(Nd,Pr)2CuO4[subscript delta] as a function of carrier doping. We revealed that, upon doping the parent Mott insulator, charge correlations first emerge in the form of rotationally-symmetric spatial density modulations, which evolve to more conventional long-ranged checkerboard order at higher doping levels. Our charge susceptibility calculations uncover a close link between the topology of charge correlations and the underlying fermiology in electron-doped cuprates and also suggest that the nature of charge correlations changes from locally incoherent charge ripples to a long-ranged broken symmetry state upon carrier doping. Using RIXS, we developed an experimental method to disentangle various electronic excitations in cuprates based on their nature. Our approach is built on the tensorial nature of the RIXS scattering matrix, whose form is imprinted onto the angular dependence of RIXS signal. Applying this method to prototypical magnetically-ordered and superconducting cuprates T'-(Nd,Pr)2CuO4[subscript -][subscript delta] and YBa2Cu3O6.75, we resolved the charge, spin, and orbital character of elastic scattering, (para-)magnon/bimagnon modes, and higher-energy intraband orbital excitations.

Author: David Shai Ellis
Publisher:
ISBN: 9780494677124
Category :
Languages : en
Pages : 354

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Excitations of the valence electrons in the high-temperature superconducting cuprate La2--xSr xCuO4 were measured by Resonant Inelastic X-ray Scattering (RIXS). Several types of electronic excitations resonant at the Cu 1s→4p transition were studied over a wide range of dopings 0 ≤ x ≤ 0.35.A 500 meV excitation was observed at a reduced momentum transfer q=(pi 0) corresponding to the zone boundary, whose temperature and doping dependence was the same as the two-magnon Raman scattering mode. The momentum dependence of this 2-magnon excitation agrees with recent theoretical calculations.Momentum resolved measurements of the x=0 sample revealed a broad range of excitations above and below the main charge transfer peak, and their dispersions were measured across the Brillouin zone. These include a dispersionless ∼1.8 eV peak, which is either a local crystal field ( d-d excitation) or dipole-forbidden charge transfer excitation, and a dispersive 2.2 eV peak identified as a Zhang-Ng type charge-transfer exciton. The 2.2 eV peak was less dispersive than predicted from the theoretical models, due to electron-phonon coupling, as illustrated by the temperature dependent shift in the peak position.With increased hole doping, the RIXS spectral weight transfers from higher to lower energies, analogous to earlier optical conductivity studies. At the finite momentum of q=(pi 0), however, the changes are most systematic: an isosbestic point was observed at 2.2 eV where the spectra of all dopings cross, and spectral weight is transferred from high to low energies, with near-linear dependence on x, in a manner suggesting that the integrated RIXS intensity is preserved. The intensity and energy variations of the spectral peaks, as well as the isosbestic point and possible sum rule, could be explained qualitatively by a rigid three-band model which includes the non-bonding oxygen, upper Hubbard, and Zhang-Rice singlet bands. The estimated properties of the bands, such as width and energy separation, are in reasonably quantitative agreement with current theoretical models and angle-resolved photoemission measurements. Moreover, anomalies in the doping dependence are similar to those observed in other types of spectroscopies. These results underscore the relevance of the RIXS method in understanding the electronic behavior of the Lanthanum cuprates.

Author: David Shai Ellis
Publisher:
ISBN: 9780494677124
Category :
Languages : en
Pages : 0

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Excitations of the valence electrons in the high-temperature superconducting cuprate La2--xSr xCuO4 were measured by Resonant Inelastic X-ray Scattering (RIXS). Several types of electronic excitations resonant at the Cu 1s & rarr;4p transition were studied over a wide range of dopings 0 & le; x & le; 0.35.A 500 meV excitation was observed at a reduced momentum transfer q=(pi 0) corresponding to the zone boundary, whose temperature and doping dependence was the same as the two-magnon Raman scattering mode. The momentum dependence of this 2-magnon excitation agrees with recent theoretical calculations. Momentum resolved measurements of the x=0 sample revealed a broad range of excitations above and below the main charge transfer peak, and their dispersions were measured across the Brillouin zone. These include a dispersionless & sim;1.8 eV peak, which is either a local crystal field (d-d excitation) or dipole-forbidden charge transfer excitation, and a dispersive 2.2 eV peak identified as a Zhang-Ng type charge-transfer exciton. The 2.2 eV peak was less dispersive than predicted from the theoretical models, due to electron-phonon coupling, as illustrated by the temperature dependent shift in the peak position. With increased hole doping, the RIXS spectral weight transfers from higher to lower energies, analogous to earlier optical conductivity studies. At the finite momentum of q=(pi 0), however, the changes are most systematic: an isosbestic point was observed at 2.2 eV where the spectra of all dopings cross, and spectral weight is transferred from high to low energies, with near-linear dependence on x, in a manner suggesting that the integrated RIXS intensity is preserved. The intensity and energy variations of the spectral peaks, as well as the isosbestic point and possible sum rule, could be explained qualitatively by a rigid three-band model which includes the non-bonding oxygen, upper Hubbard, and Zhang-Rice singlet bands. The estimated properties of the bands, such as width and energy separation, are in reasonably quantitative agreement with current theoretical models and angle-resolved photoemission measurements. Moreover, anomalies in the doping dependence are similar to those observed in other types of spectroscopies. These results underscore the relevance of the RIXS method in understanding the electronic behavior of the Lanthanum cuprates.

Author: Valentina Bisogni
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 3

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We found that in underdoped cuprate superconductors, a rich competition occurs between superconductivity and charge density wave (CDW) order. Whether rotational symmetry-breaking (nematicity) occurs intrinsically and generically or as a consequence of other orders is under debate. Here, we employ resonant x-ray scattering in stripe-ordered superconductors (La, M)2CuO4 to probe the relationship between electronic nematicity of the Cu 3d orbitals, structure of the (La, M)2O2 layers, and CDW order. We find distinct temperature dependences for the structure of the (La, M)2O2 layers and the electronic nematicity of the CuO2 planes, with only the latter being enhanced by the onset of CDW order. Our results identify electronic nematicity as an order parameter that is distinct from a purely structural order parameter in underdoped striped cuprates.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 23

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This family of intermetallic compounds is ideal for the study of the interplay between superconductivity and magnetism since, in several of these compounds (Ho, Er, Tm, Dy), superconductivity coexists with magnetic ordering. The most important findings of the scattering studies are (a) in the Ho-compound, a complex magnetic structure characterized by two incommensurate wave vectors, {rvec k}{sub a} = 0.585 {rvec a}* and {rvec k}{sub c} = 0.915 {rvec c}*, exists in the vicinity of 5 K, where the almost reentrant behavior of this compound occurs; (b) an incommensurate magnetic structure with wave vector along {rvec a}*, close to the zone boundary, is observed in several of these compounds; and (c) pronounced soft-phonon behavior was observed for both the acoustic and first optical [Delta]4[[xi]00] branches in the superconducting Lu and Ho compounds, a behavior characteristic of strongly coupled conventional superconductors. Furthermore, these phonon anomalies occur at wave vectors close to those of the incommensurate magnetically ordered structures observed in the magnetic compounds of this family. This observation suggests that both the magnetic ordering and phonon softening originate from common nesting features of the Fermi surfaces of these compounds. Band theoretical calculations are in qualitative agreement with these results.

Author: Ioannis Zegkinoglou
Publisher:
ISBN:
Category :
Languages : en
Pages : 199

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Author:
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Category :
Languages : en
Pages :

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