51 research outputs found
Dispersive charge density wave excitations and temperature dependent commensuration in Bi2Sr2CaCu2O8+{\delta}
Experimental evidence on high-Tc cuprates reveals ubiquitous charge density
wave (CDW) modulations, which coexist with superconductivity. Although the CDW
had been predicted by theory, important questions remain about the extent to
which the CDW influences lattice and charge degrees of freedom and its
characteristics as functions of doping and temperature. These questions are
intimately connected to the origin of the CDW and its relation to the
mysterious cuprate pseudogap. Here, we use ultrahigh resolution resonant
inelastic x-ray scattering (RIXS) to reveal new CDW character in underdoped
Bi2Sr2CaCu2O8+{\delta} (Bi2212). At low temperature, we observe dispersive
excitations from an incommensurate CDW that induces anomalously enhanced phonon
intensity, unseen using other techniques. Near the pseudogap temperature T*,
the CDW persists, but the associated excitations significantly weaken and the
CDW wavevector shifts, becoming nearly commensurate with a periodicity of four
lattice constants. The dispersive CDW excitations, phonon anomaly, and
temperature dependent commensuration provide a comprehensive momentum space
picture of complex CDW behavior and point to a closer relationship with the
pseudogap state
Influence of apical oxygen on the extent of in-plane exchange interaction in cuprate superconductors
In high Tc superconductors the magnetic and electronic properties are
determined by the probability that valence electrons virtually jump from site
to site in the CuO2 planes, a mechanism opposed by on-site Coulomb repulsion
and favored by hopping integrals. The spatial extent of the latter is related
to transport properties, including superconductivity, and to the dispersion
relation of spin excitations (magnons). Here, for three antiferromagnetic
parent compounds (single-layer Bi2Sr0.99La1.1CuO6+delta, double-layer
Nd1.2Ba1.8Cu3O6 and infinite-layer CaCuO2) differing by the number of apical
atoms, we compare the magnetic spectra measured by resonant inelastic x-ray
scattering over a significant portion of the reciprocal space and with
unprecedented accuracy. We observe that the absence of apical oxygens increases
the in-plane hopping range and, in CaCuO2, it leads to a genuine 3D
exchange-bond network. These results establish a corresponding relation between
the exchange interactions and the crystal structure, and provide fresh insight
into the materials dependence of the superconducting transition temperature.Comment: 9 pages, 4 figures, 1 Table, 42 reference
Intense paramagnon excitations in a large family of high-temperature superconductors
In the search for the mechanism of high-temperature superconductivity,
intense research has been focused on the evolution of the spin excitation
spectrum upon doping from the antiferromagnetic insulating to the
superconducting states of the cuprates. Because of technical limitations, the
experimental investigation of doped cuprates has been largely focused on
low-energy excitations in a small range of momentum space. Here we use resonant
inelastic x-ray scattering to show that a large family of superconductors,
encompassing underdoped YBaCuO and overdoped YBaCuO,
exhibits damped spin excitations (paramagnons) with dispersions and spectral
weights closely similar to those of magnons in undoped cuprates. %The results
are in excellent agreement with the spin excitations obtained by exact
diagonalization of the Hamiltonian on finite-sized clusters. The
comprehensive experimental description of this surprisingly simple spectrum
permits quantitative tests of magnetic Cooper pairing models. A numerical
solution of the Eliashberg equations for the magnetic spectrum of
YBaCuO reproduces its superconducting transition temperature
within a factor of two, a level of agreement comparable to Eliashberg theories
of conventional superconductors.Comment: Main text (11 pages, 4 figures) + supplementary information (4 pages,
4 figures, 1 table). An updated version will appear in Nature Physic
Spin-Orbital Separation in the quasi 1D Mott-insulator Sr2CuO3
As an elementary particle the electron carries spin \hbar/2 and charge e.
When binding to the atomic nucleus it also acquires an angular momentum quantum
number corresponding to the quantized atomic orbital it occupies (e.g., s, p or
d). Even if electrons in solids form bands and delocalize from the nuclei, in
Mott insulators they retain their three fundamental quantum numbers: spin,
charge and orbital[1]. The hallmark of one-dimensional (1D) physics is a
breaking up of the elementary electron into its separate degrees of freedom[2].
The separation of the electron into independent quasi-particles that carry
either spin (spinons) or charge (holons) was first observed fifteen years
ago[3]. Using Resonant Inelastic X-ray Scattering on the 1D Mott-insulator
Sr2CuO3 we now observe also the orbital degree of freedom separating. We
resolve an orbiton liberating itself from spinons and propagating through the
lattice as a distinct quasi-particle with a substantial dispersion of ~0.2 eV.Comment: 35 pages, 8 figure
Quartz-based flat-crystal resonant inelastic x-ray scattering spectrometer with sub-10 meV energy resolution
Momentum and polarization dependence of single-magnon spectral weight for Cu L-3-edge resonant inelastic x-ray form layered cuprates
Momentum and polarization dependence of single-magnon spectral weight for Cu L-3-edge resonant inelastic x-ray form layered cuprate
Momentum and polarization dependence of single-magnon spectral weight for Cu L3 -edge resonant inelastic x-ray scattering from layered cuprates
Recently it was predicted theoretically and confirmed experimentally that in cuprates single-magnon dispersions can be mapped out with resonant inelastic x-ray scattering (RIXS) at the copper L(3) edge. To further establish RIXS as a viable technique we investigate the momentum and
incident photon polarization dependence of the single-magnon spectral weight in a variety of layered undoped antiferromagnetic compounds. The agreement of experimental and theoretical results bolsters the assignment
of RIXS spectral features to single magnons. This detailed analysis allows
to disentangle single-magnon scattering from other spectral contributions.
Moreover, it is a necessary premise for future research aimed at
investigating processes that modulate spectral weights beyond the
predictions of linear spin-wave theory
Raman and fluorescence characteristics of resonant inelastic X-ray scattering from doped superconducting cuprates
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