We report a comprehensive Cu L3-edge resonant x-ray scattering (RXS) study of two- and three-dimensional (2D and 3D) incommensurate charge correlations in single crystals of the underdoped ...high-temperature superconductor YBa2Cu3O6.67 under uniaxial compression up to 1% along the two inequivalent Cu─O─Cu bond directions (a and b) in the CuO2 planes. We confirm the strong in-plane anisotropy of the 2D charge correlations and observe their symmetric response to pressure: pressure along a enhances correlations along b, and vice versa. Our results imply that the underlying order parameter is uniaxial. In contrast, 3D long-range charge order is only observed along b in response to compression along a. Spectroscopic RXS measurements show that the 3D charge order resides exclusively in the CuO2 planes and may thus be generic to the cuprates. We discuss implications of these results for models of electronic nematicity and for the interplay between charge order and superconductivity.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
The Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) is a new generation high-resolution γ-ray spectrometer consisting of electrically segmented high-purity germanium crystals. GRETINA is ...capable of reconstructing the energy and position of each γ-ray interaction point inside the crystal with high resolution. This enables γ-ray energy tracking which in turn provides an array with large photopeak efficiency, high resolution and good peak-to-total ratio. GRETINA is used for nuclear structure studies with demanding γ-ray detection requirements and it is suitable for experiments with radioactive-ion beams with high recoil velocities. The GRETINA array has a 1π solid angle coverage and constitutes the first stage towards the full 4π array GRETA. We present in this paper the main parts and the performance of the GRETINA system.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Resonant optical excitation of apical oxygen vibrational modes in the normal state of underdoped YBa2Cu3O6+x induces a transient state with optical properties similar to those of the equilibrium ...superconducting state. Amongst these, a divergent imaginary conductivity and a plasma edge are transiently observed in the photo-stimulated state. Femtosecond hard x-ray diffraction experiments have been used in the past to identify the transient crystal structure in this non-equilibrium state. Here, we start from these crystallographic features and theoretically predict the corresponding electronic rearrangements that accompany these structural deformations. Using density functional theory, we predict enhanced hole-doping of the CuO2 planes. The empty chain Cu dy2-z2
orbital is calculated to strongly reduce in energy, which would increase c-axis transport and potentially enhance the interlayer Josephson coupling as observed in the THz-frequency response. From these results, we calculate changes in the soft x-ray absorption spectra at the Cu L-edge. Femtosecond x-ray pulses from a free electron laser are used to probe changes in absorption at two photon energies along this spectrum and provide data consistent with these predictions.
Abstract
To provide a foundation for theoretical models of high-temperature superconductivity, experimental research has sought to establish correspondences between macroscopic transport coefficients ...on the one hand, and atomic-scale correlation functions measured by spectroscopic and scattering probes on the other hand. This research avenue has been confounded by the gradual onset of electronic ordering phenomena and of the corresponding transport anomalies. We report measurements of the uniaxial-stress dependence of the normal-state resistivity and Hall coefficient of the underdoped high-temperature superconductor YBa
2
Cu
3
O
6.67
. We observe a remarkable correspondence between the differential stress responses of the transport coefficients and resonant X-ray diffraction features indicative of charge ordering, which parallels the phenomenology of classical charge-density-wave compounds. However, our observations imply that static charge order is not responsible for a sign reversal of the Hall coefficient, and suggest that the interplay with liquid-like, dynamical charge correlations is essential for the prominent transport anomalies in the underdoped cuprates.
We study the model high-temperature superconductor HgBa(2)CuO(4+δ) with electronic Raman scattering and optical ellipsometry over a wide doping range. The dependence of the resonant Raman cross ...section on the incident photon energy changes drastically as a function of doping, in a manner that corresponds to a rearrangement of the interband optical transitions seen with ellipsometry. This doping-dependent Raman resonance allows us to reconcile the apparent discrepancy between Raman and x-ray detection of magnetic fluctuations in superconducting cuprates. Intriguingly, the strongest variation occurs across the doping level where the antinodal superconducting gap appears to reach its maximum.
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We report on the effects of hydrostatic pressure (HP) on the charge density wave observed in underdoped cuprates. We studied YBa2Cu3O6.6(Tc=61 K) using high-resolution inelastic x-ray scattering ...(IXS), and reveal an extreme sensitivity of the phonon anomalies related to the charge density wave (CDW) order to HP. The amplitudes of the normal state broadening and superconductivity-induced phonon softening at QCDW rapidly decrease as HP is applied, resulting in the complete suppression of signatures of the CDW below ∼10 kbar. Additional IXS measurements on YBa2Cu3O6.75 demonstrate that this very rapid effect cannot be explained by pressure-induced modification of the doping level and highlight the different role of external pressure and doping in tuning the phase diagram of the cuprates. Our results provide insights into the mechanisms underlying the CDW formation and its interplay with superconductivity.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
In outer space down to the altitudes routinely flown by larger aircrafts, radiation can pose serious issues for microelectronics circuits. The 88-Inch Cyclotron at Lawrence Berkeley National ...Laboratory is a sector-focused cyclotron and home of the Berkeley Accelerator Space Effects Facility, where the effects of energetic particles on sensitive microelectronics are studied with the goal of designing electronic systems for the space community. This paper describes the flexibility of the facility and its capabilities for testing the bombardment of electronics by heavy ions, light ions, and neutrons. Experimental capabilities for the generation of neutron beams from deuteron breakups and radiation testing of carbon nanotube field effect transistor will be discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Overworking is one of the most frequent stressors. The purpose of this study was to determine the effectiveness of behavioural/psycho-educational group training in men who are chronically stressed ...from overworking.
Of 72 male subjects, 36 were randomly assigned to training for 8 weeks and another 36 formed the control group, which received a placebo intervention. Primary outcome measures were systolic blood pressure, salivary cortisol concentration upon awakening, and self-reported changes on the scales of the Trier Inventory for the Assessment of Chronic Stress (TICS), the State-Trait Anger Expression Inventory (STAXI) and the 36-item Short Form Health Survey (SF-36).
A significant reduction in mean values was observed in daily systolic blood pressure and salivary cortisol concentration on all the TICS and most of the STAXI and SF-36 scales.
Behavioural/psycho-educational group training appears to be effective in the treatment of men suffering from chronic stress due to overworking.
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