N. Athanassopoulou

Specific heat and susceptibility determination of the pseudogap in YBCO7−δ

Abstract Based on the electronic specific heat and the bulk susceptibility data of oxygen-deficient YBa 2 Cu 3 O 7−δ , we present clear evidence of a pseudogap in the single-particle density of states (DOS) above T c in this system of oxide superconductors. Further analysis shows that the most likely shape of the gap is one in which the normal state DOS is zero at the Fermi level, then rises linearly and symmetrically to a cusp above the unmodified background. The size of the pseudogap is directly related with the number of lost carriers available for superconductivity and is proportional to δ. By comparing the measured entropy and the spin component of the susceptibility, we further conclude that spin and charge excitations do not separate in YBCO, and in the normal state, in this respect at least, they behave like an ordinary Fermi liquid.

Surface-quality dependence of the low temperature magnetisation of YBa2Cu3O7

Abstract The effect of the surface structure and chemistry of YBa2Cu3O7 on the low temperature (T) low field susceptibility (χ) measurements was studied. Grinding sintered material in air into particles of average radius 5 μm caused a small upturn in χ below 12 K and a larger effect was observed for smaller particles. These upturns could be removed by a suitable annealing treatment and a linear T dependence in χ, and consequently in the magnetic penetration depth was then observed. High resolution electron microscopy was used to monitor the corresponding changes in the surface structure of the particles.

Charting Exploitation Strategies for Emerging Technology

OVERVIEW: Strategy development for early-stage technology and innovation is challenging, with a need to maintain flexibility in the face of high levels of technical and commercial uncertainty. There is a demand for lightweight, agile methods that can support strategic dialogue at this stage, particularly between business functions and collaborating organizations. We have developed an “emergence roadmapping” workshop method that helps organizations to clarify the nature of a potential future value opportunity and articulate the route towards it as a series of demonstration-based milestones. The approach builds on a study of how a variety of current industries have emerged from the science and technology base in the past, allowing characterization of the phases, transitions, milestones, patterns, enablers, and barriers that may apply to current and future emergence.

High-resolution X-ray diffraction analysis of magnetically aligned high-Tc superconducting ceramics

Abstract A large range of magnetically treated superconducting ceramics has been investigated using new high-resolution X-ray diffractometers in combination with different integration techniques to obtain quantitative and qualitative results on the degree of alignment. The diffractometers combine and enhance the flexibility of a 4-circle diffractometer with the possibility to use it as a bond camera and as grazing incidence surface diffractometer. The X-ray beam is strictly monochromatic (CuKα 1 ) and focused with a long focal length on the sample. The sample goniometer can be rotated and shifted around three perpendicular axes and two translation directions, respectively. The instruments are equipped with 1D and 2D detectors and their distance to the sample can be varied between 10 and 30 cm. In our contribution we describe the experimental methods connected with this special equipment, their application to the analysis of the degree of alignment in high T c superconducting ceramics and compare the results to those obtained by standard diffraction methods.

Temperature-dependent anisotropic magnetic penetration depth of oxygen-depleted YBa2Cu3O7−δ

Abstract We have carried out systematic measurements of the anisotropic magnetic penetration depth λ ( T ) as a function of oxygen deficiency in YBa 2 Cu 3 O 7−δ on magnetically aligned powders using a direct AC susceptibility method. The oxygen-depletion range varied from δ  0 to 0.61. Although, the absolute values of λ(0) for fully oxygenated YBa 2 Cu 3 O 7−δ are consistent with previous reports, our results show a more rapid increase of the penetration depth in the ab plane, λ ab (0) with δ than previously reported. The temperature dependence of λ ( T ) is found to obey an AT + BT 2 dependence at low temperatures ( 0.04 T T c ), which is not expected for conventional s wave superconductors.

System-of-system approaches and challenges for multi-site manufacturing

In the multi-site manufacturing domain, systems-of-systems (SoS) are rarely called so. However, there exist a number of collaborative manufacturing paradigms which closely relate to system-of-system principles. These include distributed manufacturing, dispersed network manufacturing, virtual enterprises and cloud manufacturing/manufacturing-as-a-service. This paper provides an overview of these terms and paradigms, exploring their characteristics, overlaps and differences. These manufacturing paradigms are then considered in relation to five key system-of-systems characteristics: autonomy, belonging, connectivity, diversity and emergence. Data collected from two surveys of academic and industry experts is presented and discussed, with key challenges and barriers to multi-site manufacturing SoS identified.

A Thermodynamic Investigation of the Normal State Spectrum of YBa2Cu3O6+x

From a detailed comparison of the electronic specific heat and magnetic susceptibility χ of YBa2Cu3O6+x we find broad numerical agreement between the normal state electronic entropy S and aχT over a wide range of x and T, where a is the Wilson ratio for non-interacting electrons. This demonstrates that charge and spin excitations make a comparable contribution to the entropy and that the normal state pseudogap develops in both spin and charge spectra. From both S and χ we deduce a loss of ~0.338 fermion states relative to a flat band, and a pseudogap half-width ∆~440δ (K), where δ=1−x.

Cu NMR and NQR study of impurity-doped YBa2Cu3O7

Abstract The superconducting property in impurity-doped YBa 2 (Cu 1− x M x ) 3 O 7 (M=Zn and Ni) has been investigated by measuring the nuclear spin-lattice relaxation time T 1 and the Knight shift of 63 Cu in the CuO 2 plane. We have found that Zn doping into the CuO 2 plane in YBa 2 Cu 3 O 7 causes gapless superconductivity at low T , giving rise to a finite density of states at the Fermi surface, while magnetic Ni doping into the CuO 2 plane reduces T c moderately, although Ni spins behave as local moments. The gapless feature in Zn-doped YBCo 7 can be consistently interpreted in the framework of the d-wave model with gap zeros of lines at the Fermi surface, as argued for heavy-fermion superconductors.

Improving the light extraction efficiency of polymer LEDs using microcavities and photonic crystals

A significant fraction of light generated within an organic light emitting diode (OLED) is often trapped within the structure within waveguide modes and is unable to escape usefully from the device. Addressing this issue is of significant importance, as it potentially offers a route to improve the external efficiency of OLEDs. Here, we discuss a number of methods to improve light extraction efficiency from conjugated-polymer LEDs. Firstly we explore the use of low finesse optical microcavities to redistribute trapped-light into externally propagating modes. The improvements obtained by simply adopting a microcavity structure on its own are rather small, however we then show that they can be improved significantly by improving the reflectivity of the cathode. Finally, we show that by engineering a photonic crystal beneath the anode of a polymer LED, a significant improvement in external efficiency (by a factor of 2) can be achieved. Such an approach is anticipated to be readily scalable to a manufacturing environment.

Magnetoresistance and dc magnetic susceptibility of Y0.9Ca0.1Ba2Cu3O7−δ

Abstract The substitution of calcium for yttrium in YBCO has the effect of increasing the planar hole concentration. When fully oxygenated, such samples are more overdoped than normal YBCO, with optimal doping (δopt) at δ = 0.19. Specific heat data on these compounds has shown an opening of a gap in the electron density of states (the ‘pseudogap’) for δ ≥ δopt. Magnetoresistance and dc magnetic susceptibility measurements have been performed on Y0.9Ca0.1Ba2Cu3O7−δ for a range of δ from ≈ 0 to 0.92 to see if any aspects of these properties correlate with the opening of the pseudogap. In the normal state, the resistivity displays an ‘S’ shaped curve in the underdoped region. This feature has been linked to the pseudogap, but may also be analysed in terms of the increase in fluctuation conductivity; both interpretations are discussed. From the resistivity, Tc (onset) peaks for δ = δopt (at 88.7K) then drops sharply as the sample becomes underdoped. The zero field transition width begins to widen above the same point, and in 7T, field broadening, relative to Tc (onset), increases rapidly for δ > δopt. The dc magnetic susceptibility has been studied for the δ values up to 0.37, where preliminary results show the opening of a pseudogap in underdoped samples.