The concept that superconductivity competes with other orders in cuprate superconductors has become increasingly apparent, but obtaining direct evidence with bulk-sensitive probes is challenging. We ...have used resonant soft x-ray scattering to identify two-dimensional charge fluctuations with an incommensurate periodicity of ∼3.2 lattice units in the copper-oxide planes of the superconductors (Y,Nd)Ba 2 Cu 3 O 6+x , with hole concentrations of 0.09 to 0.13 per planar Cu ion. The intensity and correlation length of the fluctuation signal increase strongly upon cooling down to the superconducting transition temperature (T c ); further cooling below T c abruptly reverses the divergence of the charge correlations. In combination with earlier observations of a large gap in the spin excitation spectrum, these data indicate an incipient charge density wave instability that competes with superconductivity.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
In high-Tc superconductors the magnetic and electronic properties are determined by the probability that valence electrons jump virtually from site to site in the CuO2 planes, a mechanism opposed by ...on-site Coulomb repulsion and favoured 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 Bi2 Sr0.9 La1.1 CuO6+δ , double-layer Nd1.2 Ba1.8 Cu3 O6 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 three-dimensional (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.
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IJS, NUK, SBMB, UL, UM, UPUK
The electron-phonon interaction is a major factor influencing the competition between collective instabilities in correlated-electron materials, but its role in driving high-temperature ...superconductivity in the cuprates remains poorly understood. We have used high-resolution inelastic X-ray scattering to monitor low-energy phonons in YBa2Cu3O6.6 (superconducting transition temperature Tc = 61 K), which is close to a charge-density-wave (CDW) instability. Phonons in a narrow range of momentum space around the CDW ordering vector exhibit extremely large superconductivity-induced line-shape renormalizations. These results imply that the electron-phonon interaction has sufficient strength to generate various anomalies in electronic spectra, but does not contribute significantly to Cooper pairing. In addition, a quasi-elastic 'central peak' due to CDW nanodomains is observed in a wide temperature range above and below Tc, suggesting that the gradual onset of a spatially inhomogeneous CDW domain state with decreasing temperature is a generic feature of the underdoped cuprates.
High-temperature copper oxide superconductors consist of stacked CuO
planes, with electronic band structures and magnetic excitations that are primarily two-dimensional
, but with superconducting ...coherence that is three-dimensional. This dichotomy highlights the importance of out-of-plane charge dynamics, which has been found to be incoherent in the normal state
within the limited range of momenta accessible by optics. Here we use resonant inelastic X-ray scattering to explore the charge dynamics across all three dimensions of the Brillouin zone. Polarization analysis of recently discovered collective excitations (modes) in electron-doped copper oxides
reveals their charge origin, that is, without mixing with magnetic components
. The excitations disperse along both the in-plane and out-of-plane directions, revealing its three-dimensional nature. The periodicity of the out-of-plane dispersion corresponds to the distance between neighbouring CuO
planes rather than to the crystallographic c-axis lattice constant, suggesting that the interplane Coulomb interaction is responsible for the coherent out-of-plane charge dynamics. The observed properties are hallmarks of the long-sought 'acoustic plasmon', which is a branch of distinct charge collective modes predicted for layered systems
and argued to play a substantial part in mediating high-temperature superconductivity
.
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Although charge density waves (CDWs) are omnipresent in cuprate high-temperature superconductors, they occur at significantly different wave vectors, confounding efforts to understand their formation ...mechanism. Here, we use resonant inelastic x-ray scattering to investigate the doping- and temperature-dependent CDW evolution inLa2−xBaxCuO4(x=0.115–0.155). We discover that the CDW develops in two stages with decreasing temperature. A precursor CDW with a quasicommensurate wave vector emerges first at high temperature. This doping-independent precursor CDW correlation originates from the CDW phase mode coupled with a phonon and “seeds” the low-temperature CDW with a strongly doping-dependent wave vector. Our observation reveals the precursor CDW and its phase mode as the building blocks of the highly intertwined electronic ground state in the cuprates.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM, UPUK
One of the most intensely studied scenarios of high-temperature superconductivity (HTS) postulates pairing by exchange of magnetic excitations1. Indeed, such excitations have been observed up to ...optimal doping in the cuprates2, 3, 4, 5, 6, 7. In the heavily overdoped regime, neutron scattering measurements indicate that magnetic excitations have effectively disappeared8, 9, 10, and this has been argued to cause the demise of HTS with overdoping1, 8, 10. Here we use resonant inelastic X-ray scattering, which is sensitive to complementary parts of reciprocal space, to measure the evolution of the magnetic excitations in La2-xSrxCuO4 across the entire phase diagram, from a strongly correlated insulator (x = 0) to a non-superconducting metal (x = 0.40). For x = 0, well-defined magnon excitations are observed11. These magnons broaden with doping, but they persist with a similar dispersion and comparable intensity all the way to the non-superconducting, heavily overdoped metallic phase. The destruction of HTS with overdoping is therefore caused neither by the general disappearance nor by the overall softening of magnetic excitations. Other factors, such as the redistribution of spectral weight, must be considered. PUBLICATION ABSTRACT
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IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We used resonant inelastic x-ray scattering (RIXS) with and without analysis of the scattered photon polarization, to study dispersive spin excitations in the high temperature superconductor ...YBa_{2}Cu_{3}O_{6+x} over a wide range of doping levels (0.1≤x≤1). The excitation profiles were carefully monitored as the incident photon energy was detuned from the resonant condition, and the spin excitation energy was found to be independent of detuning for all x. These findings demonstrate that the largest fraction of the spin-flip RIXS profiles in doped cuprates arises from magnetic collective modes, rather than from incoherent particle-hole excitations as recently suggested theoretically Benjamin et al. Phys. Rev. Lett. 112, 247002 (2014). Implications for the theoretical description of the electron system in the cuprates are discussed.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Charge density modulations have been observed in all families of high-critical temperature (
) superconducting cuprates. Although they are consistently found in the underdoped region of the phase ...diagram and at relatively low temperatures, it is still unclear to what extent they influence the unusual properties of these systems. Using resonant x-ray scattering, we carefully determined the temperature dependence of charge density modulations in YBa
Cu
O
and Nd
Ba
Cu
O
for several doping levels. We isolated short-range dynamical charge density fluctuations in addition to the previously known quasi-critical charge density waves. They persist up to well above the pseudogap temperature
, are characterized by energies of a few milli-electron volts, and pervade a large area of the phase diagram.
•A Transfer Matrix Method for infinite multilayered cylinders has been developed.•Interactions with internal and external fluid media are modelled analytically.•Diffuse acoustic field excitation has ...been considered.•The method was validated by comparison with analytical solutions.•The acoustic transmission through heterogeneous cylinders has been predicted.
This paper discusses the use of a Transfer Matrix (TM) method for predicting the acoustic behavior of infinite cylinders consisting of a generic arrangement of homogeneous and heterogeneous periodic layers of various nature (fluid, solid, poroelastic). A through-radius TM is derived for a layer characterized by cylindrical periodicity by manipulating the dynamic stiffness matrix related to a finite element model of a unit cell. The proposed technique is equally appealing for homogeneous layers since few elements are needed in this case. In such a framework, different layers can be combined to form multilayered systems and the related acoustic radiation or transmission due to an external plane wave or a diffuse acoustic field can be assessed. The proposed approach is validated in case of cylinders consisting of homogeneous layers by comparison with alternative approaches. In order to demonstrate the usefulness of the approach, the sound transmission through a cylindrical structure with resonators is presented.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Electronic inhomogeneity appears to be an inherent characteristic of the enigmatic cuprate superconductors. Here we report the observation of charge-density-wave correlations in the model cuprate ...superconductor HgBa2 CuO4+δ (Tc =72 K) via bulk Cu L3 -edge-resonant X-ray scattering. At the measured hole-doping level, both the short-range charge modulations and Fermi-liquid transport appear below the same temperature of about 200 K. Our result points to a unifying picture in which these two phenomena are preceded at the higher pseudogap temperature by q=0 magnetic order and the build-up of significant dynamic antiferromagnetic correlations. The magnitude of the charge modulation wave vector is consistent with the size of the electron pocket implied by quantum oscillation and Hall effect measurements for HgBa2 CuO4+δ and with corresponding results for YBa2 Cu3 O6+δ , which indicates that charge-density-wave correlations are universally responsible for the low-temperature quantum oscillation phenomenon.
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