The concept that superconductivity competes with other orders in cuprate superconductors has beco... more 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_2Cu_3O_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.
We have performed a detailed resonant x-ray scattering ͑RXS͒ study at the Mn K edge of LaMnO 3 by... more We have performed a detailed resonant x-ray scattering ͑RXS͒ study at the Mn K edge of LaMnO 3 by measuring the ͑h ,0,0͒, ͑0,k ,0͒ and ͑0,0,l͒ forbidden reflections ͑h , k , l =3,5͒ between 10 and 300 K in the channel. For all three types of reflections we observed strong resonant peaks presenting the sin 2 intensity modulation as a function of the azimuth scanning angle , characteristic of dipolar transitions. Their origin was ascribed to anisotropic tensor scattering, since no change either in energy line shape or in intensity was observed when crossing the Néel temperature at ϳ140 K. Integrated intensities were roughly constant up to 300 K, contrary to previous reports found in the literature. The energy dependence of the scattered intensity for the ͑h ,0,0͒ and ͑0,k ,0͒ reflections was identical but different from the ͑0,0,l͒ reflection. All reflections have been explained within multiple scattering theory in terms of long-range structural distortions around Mn atoms, without invoking any kind of 3d orbital ordering. We also studied the energy dependence of the principal axes of the anomalous-scattering tensor in a case, like the present one, where the scattering atoms do not possess any point-symmetry axes. We found that they are not constant with the photon energy, implying the absence of a direct correlation between RXS and quadrupolar charge distribution in the ground state.
Recently, charge density wave (CDW) order in the CuO 2 planes of underdoped YBa 2 Cu 3 O 6þ was d... more Recently, charge density wave (CDW) order in the CuO 2 planes of underdoped YBa 2 Cu 3 O 6þ was detected using resonant soft x-ray scattering. An important question remains: is the chain layer responsible for this charge ordering? Here, we explore the energy and polarization dependence of the resonant scattering intensity in a detwinned sample of YBa 2 Cu 3 O 6:75 with ortho-III oxygen ordering in the chain layer. We show that the ortho-III CDW order in the chains is distinct from the CDW order in the planes. The ortho-III structure gives rise to a commensurate superlattice reflection at Q ¼ ½0:33 0 L whose energy and polarization dependence agrees with expectations for oxygen ordering and a spatial modulation of the Cu valence in the chains. Incommensurate peaks at [0.30 0 L] and [0 0.30 L] from the CDW order in the planes are shown to be distinct in Q as well as their temperature, energy, and polarization dependence, and are thus unrelated to the structure of the chain layer. Moreover, the energy dependence of the CDW order in the planes is shown to result from a spatial modulation of energies of the Cu 2p to 3d x 2 Ày 2 transition, similar to stripe-ordered 214 cuprates.
In order to better constrain the interpretation and the nature of the seismic reflectors, experim... more In order to better constrain the interpretation and the nature of the seismic reflectors, experimental measurements at high confining pressure (up to 300 MPa) and room temperature of the compressional wave velocity (Vp) on 10 samples representative of the most common lithologies along the Aurina (Ahrntal), Tures (Tauferer Tal), and Badia (Abtei Tal) Valleys profile (Eastern Alps, Italy) have been performed. For each sample, the speed of ultrasonic waves was measured in three mutually perpendicular directions, parallel and normal to the rock foliation and lineation.
We report here on a detailed coherent x-ray diffraction study of the charge-density wave in K 0.3... more We report here on a detailed coherent x-ray diffraction study of the charge-density wave in K 0.3 MoO 3 as a function of an external current. At threshold current, the charge-density wave undergoes a strong decrease of average amplitude keeping large correlation lengths. At the same time, an extra electronic modulation with large periodicity appears directly related to the sliding of the charge-density wave. This effect is interpreted as the formation of a soliton lattice and its evolution with respect to external current is investigated. The charge-density wave phase is found to undergo an anharmonic to harmonic transition when a current is injected.
We present a direct study of the Co charge order and Na ordering in three Co-layers NaxCoO2 ( xti... more We present a direct study of the Co charge order and Na ordering in three Co-layers NaxCoO2 ( xtilde (5)/(6)) single crystals. From diffuse scattering measurements, we propose a model of Na supercell which rules out the ones previously suggested in parent cobaltates with double Co layers. Via a direct measurement of the Co charge state using anomalous x-ray scattering, we also evidence a Co charge order which evolves between 200 and 290 K.
Journal of Superconductivity and Novel Magnetism, 2011
Non-resonant and element specific magnetic X-ray scattering has been used to determine the orient... more Non-resonant and element specific magnetic X-ray scattering has been used to determine the orientation of Eu and Fe magnetic moments in EuFe 2 As 2 iron pnictide. Experiments have been carried out on single crystal samples at the ESRF.
We investigated the electric field gradient tensor at the Cu nuclei by Zeeman perturbed nuclear q... more We investigated the electric field gradient tensor at the Cu nuclei by Zeeman perturbed nuclear quadrupole resonance in orbitally ordered KCuF3. Our data show the presence of two inequivalent crystallographic sites with distinct orientations of the copper wave function, compatibly with the proposed orbital order for this compound. An unusual behaviour of the paramagnetic NQR signal at the Néel transition
The European Physical Journal Special Topics, 2012
The polarization of x-rays plays an outstanding role in experimental techniques such as non-reson... more The polarization of x-rays plays an outstanding role in experimental techniques such as non-resonant magnetic x-ray scattering and resonant x-ray scattering of magnetic and multipolar order. Different instrumental methods applied to synchrotron light can transform its natural polarization into an arbitrary polarization state. Several synchrotron applications, in particular in the field of magnetic and resonant scattering rely on the improvement in the signal/noise ratio or the deeper insight into the ordered state and the scattering process made possible through these polarization techniques. Here, we present the mathematical framework for the description of fully and partially polarized x-rays, with some applications such as linear x-ray polarization analysis for the determination of the scattered beam's polarization, and the Ge K-edge resonant scattering.
Biotites from metapelitic xenoliths included within trachytes from the Euganean Hills (Italy) wer... more Biotites from metapelitic xenoliths included within trachytes from the Euganean Hills (Italy) were analyzed by single-crystal X-ray diffraction (XRD), electron microprobe (EMP), scanning electron microscope (SEM), secondary ion mass spectrometry (SIMS), and Mössbauer spectroscopy. These biotites are Ti-rich and occur in gneissic xenoliths that underwent regional high-T/low-P metamorphism, at about 750 °C, followed by pyrometamorphism during incorporation in the melt at temperatures close to 950 °C.
Pseudomorphic sericite aggregates after staurolite have been observed in garnet + staurolite +/- ... more Pseudomorphic sericite aggregates after staurolite have been observed in garnet + staurolite +/- kyanite micaschists from the Austroalpine basement outcropping in the Quaira (Karbach) Valley (Eastern Alps, Bolzano, Italy). Microstructural analysis, mineral assemblages and geothermobarometry give constraints on the Variscan metamorphic peak conditions (T = 600-650° C; P = 0.7-0.8 GPa) and on the subsequent retrogressive P-T path. Reaction microstructures have been analysed by optical microscopy and SEM, and a developing model has been proposed. Such a model resulted to be satisfactory although some approximations have been introduced. These are related to inhomogeneous distribution of mineral phases in the matrix and to the exclusion of some mineral phases (garnet and plagioclase) believed to be not relevant to the pseudomorph formation. The following reaction is predicted by the model: 1.00 St + 2.42 Bt + 4.76 Qtz + 26.2 H2O = 2.73 Ms + 3.56 Chl + 0.24 Ilm. Congruently to observations, this reaction predicts that staurolite porphyroblasts decomposition to sericite is strictly connected to biotite decomposition to chlorite + ilmenite in the matrix. In fact, although channelised fluids probably drove the reaction, the extent of staurolite decomposition resulted to be controlled by the availability of biotite in the matrix.
The concept that superconductivity competes with other orders in cuprate superconductors has beco... more 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_2Cu_3O_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.
We have performed a detailed resonant x-ray scattering ͑RXS͒ study at the Mn K edge of LaMnO 3 by... more We have performed a detailed resonant x-ray scattering ͑RXS͒ study at the Mn K edge of LaMnO 3 by measuring the ͑h ,0,0͒, ͑0,k ,0͒ and ͑0,0,l͒ forbidden reflections ͑h , k , l =3,5͒ between 10 and 300 K in the channel. For all three types of reflections we observed strong resonant peaks presenting the sin 2 intensity modulation as a function of the azimuth scanning angle , characteristic of dipolar transitions. Their origin was ascribed to anisotropic tensor scattering, since no change either in energy line shape or in intensity was observed when crossing the Néel temperature at ϳ140 K. Integrated intensities were roughly constant up to 300 K, contrary to previous reports found in the literature. The energy dependence of the scattered intensity for the ͑h ,0,0͒ and ͑0,k ,0͒ reflections was identical but different from the ͑0,0,l͒ reflection. All reflections have been explained within multiple scattering theory in terms of long-range structural distortions around Mn atoms, without invoking any kind of 3d orbital ordering. We also studied the energy dependence of the principal axes of the anomalous-scattering tensor in a case, like the present one, where the scattering atoms do not possess any point-symmetry axes. We found that they are not constant with the photon energy, implying the absence of a direct correlation between RXS and quadrupolar charge distribution in the ground state.
Recently, charge density wave (CDW) order in the CuO 2 planes of underdoped YBa 2 Cu 3 O 6þ was d... more Recently, charge density wave (CDW) order in the CuO 2 planes of underdoped YBa 2 Cu 3 O 6þ was detected using resonant soft x-ray scattering. An important question remains: is the chain layer responsible for this charge ordering? Here, we explore the energy and polarization dependence of the resonant scattering intensity in a detwinned sample of YBa 2 Cu 3 O 6:75 with ortho-III oxygen ordering in the chain layer. We show that the ortho-III CDW order in the chains is distinct from the CDW order in the planes. The ortho-III structure gives rise to a commensurate superlattice reflection at Q ¼ ½0:33 0 L whose energy and polarization dependence agrees with expectations for oxygen ordering and a spatial modulation of the Cu valence in the chains. Incommensurate peaks at [0.30 0 L] and [0 0.30 L] from the CDW order in the planes are shown to be distinct in Q as well as their temperature, energy, and polarization dependence, and are thus unrelated to the structure of the chain layer. Moreover, the energy dependence of the CDW order in the planes is shown to result from a spatial modulation of energies of the Cu 2p to 3d x 2 Ày 2 transition, similar to stripe-ordered 214 cuprates.
In order to better constrain the interpretation and the nature of the seismic reflectors, experim... more In order to better constrain the interpretation and the nature of the seismic reflectors, experimental measurements at high confining pressure (up to 300 MPa) and room temperature of the compressional wave velocity (Vp) on 10 samples representative of the most common lithologies along the Aurina (Ahrntal), Tures (Tauferer Tal), and Badia (Abtei Tal) Valleys profile (Eastern Alps, Italy) have been performed. For each sample, the speed of ultrasonic waves was measured in three mutually perpendicular directions, parallel and normal to the rock foliation and lineation.
We report here on a detailed coherent x-ray diffraction study of the charge-density wave in K 0.3... more We report here on a detailed coherent x-ray diffraction study of the charge-density wave in K 0.3 MoO 3 as a function of an external current. At threshold current, the charge-density wave undergoes a strong decrease of average amplitude keeping large correlation lengths. At the same time, an extra electronic modulation with large periodicity appears directly related to the sliding of the charge-density wave. This effect is interpreted as the formation of a soliton lattice and its evolution with respect to external current is investigated. The charge-density wave phase is found to undergo an anharmonic to harmonic transition when a current is injected.
We present a direct study of the Co charge order and Na ordering in three Co-layers NaxCoO2 ( xti... more We present a direct study of the Co charge order and Na ordering in three Co-layers NaxCoO2 ( xtilde (5)/(6)) single crystals. From diffuse scattering measurements, we propose a model of Na supercell which rules out the ones previously suggested in parent cobaltates with double Co layers. Via a direct measurement of the Co charge state using anomalous x-ray scattering, we also evidence a Co charge order which evolves between 200 and 290 K.
Journal of Superconductivity and Novel Magnetism, 2011
Non-resonant and element specific magnetic X-ray scattering has been used to determine the orient... more Non-resonant and element specific magnetic X-ray scattering has been used to determine the orientation of Eu and Fe magnetic moments in EuFe 2 As 2 iron pnictide. Experiments have been carried out on single crystal samples at the ESRF.
We investigated the electric field gradient tensor at the Cu nuclei by Zeeman perturbed nuclear q... more We investigated the electric field gradient tensor at the Cu nuclei by Zeeman perturbed nuclear quadrupole resonance in orbitally ordered KCuF3. Our data show the presence of two inequivalent crystallographic sites with distinct orientations of the copper wave function, compatibly with the proposed orbital order for this compound. An unusual behaviour of the paramagnetic NQR signal at the Néel transition
The European Physical Journal Special Topics, 2012
The polarization of x-rays plays an outstanding role in experimental techniques such as non-reson... more The polarization of x-rays plays an outstanding role in experimental techniques such as non-resonant magnetic x-ray scattering and resonant x-ray scattering of magnetic and multipolar order. Different instrumental methods applied to synchrotron light can transform its natural polarization into an arbitrary polarization state. Several synchrotron applications, in particular in the field of magnetic and resonant scattering rely on the improvement in the signal/noise ratio or the deeper insight into the ordered state and the scattering process made possible through these polarization techniques. Here, we present the mathematical framework for the description of fully and partially polarized x-rays, with some applications such as linear x-ray polarization analysis for the determination of the scattered beam's polarization, and the Ge K-edge resonant scattering.
Biotites from metapelitic xenoliths included within trachytes from the Euganean Hills (Italy) wer... more Biotites from metapelitic xenoliths included within trachytes from the Euganean Hills (Italy) were analyzed by single-crystal X-ray diffraction (XRD), electron microprobe (EMP), scanning electron microscope (SEM), secondary ion mass spectrometry (SIMS), and Mössbauer spectroscopy. These biotites are Ti-rich and occur in gneissic xenoliths that underwent regional high-T/low-P metamorphism, at about 750 °C, followed by pyrometamorphism during incorporation in the melt at temperatures close to 950 °C.
Pseudomorphic sericite aggregates after staurolite have been observed in garnet + staurolite +/- ... more Pseudomorphic sericite aggregates after staurolite have been observed in garnet + staurolite +/- kyanite micaschists from the Austroalpine basement outcropping in the Quaira (Karbach) Valley (Eastern Alps, Bolzano, Italy). Microstructural analysis, mineral assemblages and geothermobarometry give constraints on the Variscan metamorphic peak conditions (T = 600-650° C; P = 0.7-0.8 GPa) and on the subsequent retrogressive P-T path. Reaction microstructures have been analysed by optical microscopy and SEM, and a developing model has been proposed. Such a model resulted to be satisfactory although some approximations have been introduced. These are related to inhomogeneous distribution of mineral phases in the matrix and to the exclusion of some mineral phases (garnet and plagioclase) believed to be not relevant to the pseudomorph formation. The following reaction is predicted by the model: 1.00 St + 2.42 Bt + 4.76 Qtz + 26.2 H2O = 2.73 Ms + 3.56 Chl + 0.24 Ilm. Congruently to observations, this reaction predicts that staurolite porphyroblasts decomposition to sericite is strictly connected to biotite decomposition to chlorite + ilmenite in the matrix. In fact, although channelised fluids probably drove the reaction, the extent of staurolite decomposition resulted to be controlled by the availability of biotite in the matrix.
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Papers by C. Mazzoli