Scaling of the superfluid density in severely underdoped YBa2Cu3O6+y

Recent measurements on extremely-underdoped YBa2Cu3O6+y [Phys. Rev. Lett. 99, 237003 (2007)] have allowed the critical temperature (T_c), superfluid density [rho_0 (T << T_c)] and dc conductivity [sigma_dc (T ~ T_c)] to be determined for a series of electronic dopings for T_c ~ 3 - 17 K. The general scaling relation rho_0/8 ~ 4.4 sigma_dc T_c is observed, extending the validity of both the ab-plane and c-axis scaling an order of magnitude and creating a region of overlap. This suggests that severely underdoped materials may constitute a Josephson phase; as the electronic doping is increased a more uniform superconducting state emerges.Comment: 5 pages, 3 figure

Charge order, metallic behavior and superconductivity in La_{2-x}Ba_xCuO_4 with x=1/8

The ab-plane optical properties of a cleaved single crystal of La_{2-x}Ba_xCuO_4 for x=1/8 (T_c ~ 2.4 K) have been measured over a wide frequency and temperature range. The low-frequency conductivity is Drude-like and shows a metallic response with decreasing temperature. However, below ~ 60 K, corresponding to the onset of charge-stripe order, there is a rapid loss of spectral weight below about 40 meV. The gapping of single-particle excitations looks surprisingly similar to that observed in superconducting La_{2-x}Sr_{x}CuO_4, including the presence of a residual Drude peak with reduced weight; the main difference is that the lost spectral weight moves to high, rather than zero, frequency, reflecting the absence of a bulk superconducting condensate.Comment: 4 pages, with 1 table and 3 figure

Risk, commercialism and social purpose: Repositioning the English housing association sector

Originally seen as the ‘third arm’ of UK housing policy, the independent, not-for-profit housing association sector had long been seen as effective in ‘filling the gap’ where the state or market were unable to provide for households in need. Since the 1980s in particular, successive governments had viewed housing associations in favourable terms as efficient, semi-autonomous social businesses, capable of leveraging significant private funding. By 2015, in contrast, central government had come to perceive the sector as inefficient, bureaucratic and wasteful of public subsidy. Making use of institutional theory, this paper considers this paradigm shift and examines the organisational responses to an increasingly challenging operating environment. By focusing, in particular, on large London housing associations, the paper analyses their strategic decision-making to address the opportunities and threats presented. The paper argues that in facing an era of minimal subsidy, low security and high risk, the 2015 reforms represent a critical juncture for the sector. Housing organisations face a stark dilemma about whether to continue a strategy of ‘profit for purpose’ or to embrace an unambiguously commercial ethos. The article contends that the trajectory of decision-making (although not unidirectional) leads ultimately towards an increased exposure to risk and vulnerability to changes in the housing market. More fundamentally, the attempt to reconcile social and commercial logics is likely to have wider consequences for the legitimacy of the sector

Infrared Optical Properties of Ferropericlase (Mg1-xFexO): Experiment and Theory

The temperature dependence of the reflectance spectra of magnesium oxide (MgO) and ferropericlase (Mg1-xFexO, for x=0.06 and x=0.27) have been measured over a wide frequency range (~50 to 32000 cm-1) at 295 and 6 K. The complex dielectric function has been determined from a Kramers-Kronig analysis of the reflectance. The spectra of the doped materials resembles pure MgO in the infrared region, but with much broader resonances. We use a shell model to calculate the dielectric function of ferropericlase, including both anharmonic phonon-phonon interactions and disorder scattering. These data are relevant to understanding the heat conductivity of ferropericlase in the earth's lower mantle.Comment: 17 pages, 6 figure

Doping of a One-Dimensional Mott Insulator: Photoemision and Optical Studies of Sr2_2CuO3+δ_{3+\delta}

The spectral properties of a one-dimensional (1D) single-chain Mott insulator Sr$_2$CuO$_{3}$ have been studied in angle-resolved photoemission and optical spectroscopy, at half filling and with small concentrations of extra charge doped into the chains via high oxygen pressure growth. The single- particle gap is reduced with oxygen doping, but the metallic state is not reached. The bandwidth of the charge-transfer band increases with doping, while the state becomes narrower, allowing unambiguous observation of separated spinon and holon branches in the doped system. The optical gap is not changed upon doping, indicating that a shift of chemical potential rather than decrease of corelation gap is responsible for the apparent reduction of the photoemission gap.Comment: 4 pages, 2 figure

Perfect separation of intraband and interband excitations in PdCoO2_2

The temperature dependence of the optical properties of the delafossite PdCoO$_2$ has been measured in the a-b planes over a wide frequency range. The optical conductivity due to the free-carrier (intraband) response falls well below the interband transitions, allowing the plasma frequency to be determined from the $f$-sum rule. Drude-Lorentz fits to the complex optical conductivity yield estimates for the free-carrier plasma frequency and scattering rate. The in-plane plasma frequency has also been calculated using density functional theory. The experimentally-determined and calculated values for the plasma frequencies are all in good agreement; however, at low temperature the optically-determined scattering rate is much larger than the estimate for the transport scattering rate, indicating a strong frequency-dependent renormalization of the optical scattering rate. In addition to the expected in-plane infrared-active modes, two very strong features are observed that are attributed to the coupling of the in-plane carriers to the out-of-plane longitudinal optic modes.Comment: 7 pages with five figures and three tables; 4 pages of supplementary materia

Comprehensive Animal Control

In 1974 the Executive Committee of the Vancouver Regional Branch of the B.C.S.P.C.A. began investigating factors that influence the pet population. Specific attention was given to the changing sociological environment of the area as well as techniques for the control of the pet population and its growth. Some of the sociological problems found in the survey were as follows. Massive increases in multi-unit dwellings such as condominiums and apartment blocks had changed the living space available for both humans and animals. In addition, the actual role of the dog in society had changed in many instances. People were choosing larger dogs to fulfill the role of both pet and guard dog. Dog sizes increased over five years from 22.4 pounds to 51.8 pounds

Quantifying the state of the coral reef ecosystem in relation to biophysical benthic and pelagic indicators and biological drivers of change in the Saba National Marine Park, Dutch Caribbean

Coral reefs are experiencing large scale degradation. Motivated by the need for regular data monitoring and for quantification of the state and change of benthic and pelagic organisms, the Global Coral Reef Monitoring Network protocol was executed on 18 dive sites in fished and unfished areas around the island of Saba in the Saba National Marine Park (SNMP) in the Dutch Caribbean from March to May 2019. Pictures of the benthos were taken and analysed with the Coral Point Count Excel extension software and fish biomass was calculated through the Bayesian length-weight-relationship. Although considerably below the Caribbean-wide average, coral cover around the island seems to be slowly recovering from past diseases and hurricane events. Coral species richness positively correlates with reef fish density and Serranidae species richness. As in other parts of the Caribbean, macroalgae in the SNMP are rapidly spreading and increasingly compete for space with habitat-providing gorgonians, sponges and other benthic organisms. In contrast to expectations, fish density and biomass continue to increase, even in zones where fishing is allowed. This might be explained by the higher availability of macroalgae that serve as food for various herbivorous fish species, which in turn are, amongst others, the prey of predatory fish and those higher up in the trophic cascade. However, with the exception of the commercially important fish family Lutjanidae all key fish species have declined in average size in recent years. Another finding is the increase of coral diseases. The results indicate the need for further species-specific research in order to identify the factors that are causing the degradation of the reefs in the SNMP. A better understanding of the interactions, ecological roles and functions of benthic and fish communities is therefore essential for the protection of reefs, that are of high value to Saba. The results of this study contribute to the adaptive management of the Saba Conservation Foundation that manages the SNMP

The fate of quasiparticles in the superconducting state

Quasiparticle properties in the superconducting state are masked by the superfluid and are not directly accessible to infrared spectroscopy. We show how one can use a Kramers--Kronig transformation to separate the quasiparticle from superfluid response and extract intrinsic quasiparticle properties in the superconducting state. We also address the issue of a narrow quasiparticle peak observed in microwave measurements, and demonstrate how it can be combined with infrared measurements to obtain unified picture of electrodynamic properties of cuprate superconductors