No abstract

Recent theories of charge-density-wave (CDW) order in high-temperature superconductors have predicted a primarily d CDW orbital symmetry. Here, we report on the orbital symmetry of CDW order in the canonical cuprate superconductors La1.875Ba0.125CuO4 (LBCO) and YBa2Cu3O6.67 (YBCO), using resonant soft X-ray scattering and a model mapped to the CDW orbital symmetry. From measurements sensitive to the O sublattice, we conclude that LBCO has predominantly s' CDW orbital symmetry, in contrast to the d orbital symmetry recently reported in other cuprates. Furthermore, we show for YBCO that the CDW orbital symmetry differs along the a and b crystal axes and that these both differ from LBCO. This work highlights CDW orbital symmetry as an additional key property that distinguishes the different cuprate families. We discuss how the CDW symmetry may be related to the '1/8-anomaly' and to static spin ordering.

The competition between superconductivity and charge density wave (CDW) order in underdoped cuprates has now been widely reported, but the role of disorder in this competition has yet to be fully resolved. A central question is whether disorder sets the length scale of the CDW order, for instance by pinning charge density fluctuations or disrupting an otherwise long range order. Using resonant soft x-ray scattering, we investigate the sensitivity of CDW order in YBa2Cu3O6+x (YBCO) to varying levels of oxygen disorder. We find that quench cooling YBCO6.67 (YBCO6.75) crystals to destroy their o-V and o-VIII (o-III) chains decreases the intensity of the CDW superlattice peak by a factor of 1.9 (1.3), but has little effect on the CDW correlation length, incommensurability, and temperature dependence. This reveals that while quenched oxygen disorder influences the CDW order parameter, the spatial extent of the CDW order is insensitive to the level of quenched oxygen disorder and may instead be a consequence of competition with superconductivity.Charge density wave (CDW) order has been solidified as a generic property and principal competitor to superconductivity (SC) [5] Within such interpretations, the common short range character of CDW order in the cuprates is associated with each material's specific defect properties and crystal structure. However, it is also possible that such descriptions only apply due to the high defect strength, masking a more generic and intrinsic origin of this length scale, such as the competition of CDW order with superconductivity. [20,21] To address this question, we turn to high-purity, oxygen ordered YBCO. With regards to defects, YBCO represents a special case in the cuprates since stoichiometric, ultra-high purity crystals can be grown with low levels of cation disorder.[22] Doping of the CuO 2 planes occurs by the addition of oxygen atoms into the chain layer, which can organize into a number of ortho-ordered phases depending on the oxygen content. [23][24][25] Disorder in these CuO chains have been shown by microwave conductivity studies of quasiparticle scattering in YBCO 6.5 to be the dominant source of weak-limit scattering, [26] indicating that the most influential defects in YBCO reside in the chain layer.[15] As previously established, the oxygen ordered states can be intentionally destroyed by heating YBCO crystals to modest temperatures and subsequently quench cooling to prevent the formation of chain order. [25][26][27][28] This allows for individual crystals of YBCO to be investigated with varying degrees of disorder.In this Letter, we exploit this means of controlling disorder in YBCO to study the effect of quenched disorder on CDW order in the cuprates using resonant soft x-ray scattering (RSXS). Our main finding is that disordering the chains decreases the CDW scattering intensity, but has little impact on the CDW correlation length (ξ CDW ), incommensurability or T dependence. This reveals that while disorder influences the CDW order parameter, the length scale of...

A 4-section semiconductor laser with integrated optical feedback has been shown experimentally to be capable of operating in either the short- or long-cavity regime, by controlling the device relaxation oscillation frequency relative to the external cavity frequency. Systematic increase of the laser injection current, and the resulting increase in relaxation oscillation frequency, allowed the transition between the two regimes of operation to be observed. The system displayed a gradual transition from a dynamic dominated by regular pulse packages in the short-cavity regime to one dominated by broadband chaotic output when operating in the long-cavity regime. This suggests that the "short cavity" regular pulse packages continue to co-exist with the "long cavity" broadband chaotic dynamic in the system studied. It is the relative power associated with each of these dynamics that changes. This may occur more generally in similar systems.

We report C(1s) and O(1s) surface sensitive x-ray photoelectron spectroscopy (XPS) and C and O K-edge partial-electron yield near-edge x-ray absorption fine structure (NEXAFS) measurements for (100) and (110) oxidized diamond surfaces, etched by a laser two-photon ultraviolet (UV) desorption process. Etched regions of the (100) surface show increased oxygen coverage with a higher fraction of singly bonded termination species than unetched regions. Similar changes are observed for the (110) but with smaller magnitude. For both surfaces, no major change in sp 2 bonded carbon is observed. We show that the terminations observed for etched surfaces are consistent with the formation of oxidized {111} facets. For deeply etched samples, atomic force microscopy and scanning electron microscopy confirm the presence of {111}-like facets and reveals the development of nanoscale facetted ridges directed perpendicular to the etching beam polarization. An etching mechanism is proposed involving localized optical absorption by surface electronic states, with the probability for subsequent desorption events varying according to the relative directions of laser polarization and lattice orientation.