Possible Microscopic Doping Mechanism in Tl-2201

X-ray absorption spectroscopy on oxygen-annealed, self-flux-grown single crystals of Tl-2201 suggests a microscopic doping mechanism whereby interstitial oxygens are attracted to copper substituted on the thallium site, contributing holes to both the planes and to these coppers, and typically promoting only one hole to the plane rather than two. These copper substituents would provide an intrinsic hole doping. The evidence for this is discussed, along with an alternative interpretation.Comment: 2 pages, 1 figure, submitted as conference proceedings for M2S-IX, Toky

Field-induced thermal metal-to-insulator transition in underdoped LSCO

The transport of heat and charge in cuprates was measured in undoped and heavily-underdoped single crystal La_{2-x}Sr_xCuO_{4+delta} (LSCO). In underdoped LSCO, the thermal conductivity is found to decrease with increasing magnetic field in the T --> 0 limit, in striking contrast to the increase observed in all superconductors, including cuprates at higher doping. The suppression of superconductivity with magnetic field shows that a novel thermal metal-to-insulator transition occurs upon going from the superconducting state to the field-induced normal state.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding

Multiband superconductivity in NbSe_2 from heat transport

The thermal conductivity of the layered s-wave superconductor NbSe_2 was measured down to T_c/100 throughout the vortex state. With increasing field, we identify two regimes: one with localized states at fields very near H_c1 and one with highly delocalized quasiparticle excitations at higher fields. The two associated length scales are most naturally explained as multi-band superconductivity, with distinct small and large superconducting gaps on different sheets of the Fermi surface.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding

Doping dependence of superconducting gap in YBa_2Cu_3O_y from universal heat transport

Thermal transport in the T -> 0 limit was measured as a function of doping in high-quality single crystals of the cuprate superconductor YBa_2Cu_3O_y. The residual linear term kappa_0/T is found to decrease as one moves from the overdoped regime towards the Mott insulator region of the phase diagram. The doping dependence of the low-energy quasiparticle gap extracted from kappa_0/T is seen to scale closely with that of the pseudogap, arguing against a non-superconducting origin for the pseudogap. The presence of a linear term for all dopings is evidence against the existence of a quantum phase transition to an order parameter with a complex (ix) component.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding

Revealing orbital and magnetic phase transitions in Pr0.5Ca0.5MnO3 epitaxial thin films by resonant soft x-ray scattering

Coherent epitaxial growth allows us to produce strained crystalline films with structures that are unstable in the bulk. Thereby, the overlayer lattice parameters in the interface plane, (a, b), determine theminimum-energy out-of-plane lattice parameter, cmin (a, b).We showbymeans of density-functional total energy calculations that this dependence can be discontinuous and predict related firstorder phase transitions in strained tetragonal films of the elements V, Nb, Ru, La, Os, and Ir. The abrupt change of cmin can be exploited to switch properties specific to the overlayer material. This is demonstrated for the example of the superconducting critical temperature of a vanadium film which we predict to jump by 20% at a discontinuity of cmin

Field-induced quantum critical point in CeCoIn_5

The resistivity of CeCoIn_5 was measured down to 20 mK in magnetic fields of up to 16 T. With increasing field, we observe a suppression of the non-Fermi liquid behavior, rho~T, and the development of a Fermi liquid state, with its characteristic rho=rho_0+AT^2 dependence. The field dependence of the T^2 coefficient shows critical behavior with an exponent of ~4/3. This is evidence for a new field-induced quantum critical point, occuring in this case at a critical field which coincides with the superconducting upper critical field H_c2.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding

Magnetic Frustration in a Mn Honeycomb Lattice Induced by Mn-O-O-Mn Pathways

We investigated the electronic structure of layered Mn oxide Bi3Mn4O12(NO3) with a Mn honeycomb lattice by x-ray absorption spectroscopy. The valence of Mn was determined to be 4+ with a small charge-transfer energy. We estimated the values of superexchange interactions up to the fourth nearest neighbors (J1, J2, J3, and J4) by unrestricted Hartree-Fock calculations and a perturbation method. We found that the absolute values of J1 through J4 are similar with positive (antiferromagnetic) J1 and J4, and negative (ferromagnetic) J2 and J3, due to Mn-O-O-Mn pathways activated by the smallness of charge-transfer energy. The negative J3 provides magnetic frustration in the honeycomb lattice to prevent long-range ordering.Comment: 4 pages, 3 figure

Fully Gapped Single-Particle Excitations in the Lightly Doped Cuprates

The low-energy excitations of the lightly doped cuprates were studied by angle-resolved photoemission spectroscopy. A finite gap was measured over the entire Brillouin zone, including along the d_{x^2 - y^2} nodal line. This effect was observed to be generic to the normal states of numerous cuprates, including hole-doped La_{2-x}Sr_{x}CuO_{4} and Ca_{2-x}Na_{x}CuO_{2}Cl_{2} and electron-doped Nd_{2-x}Ce_{x}CuO_{4}. In all compounds, the gap appears to close with increasing carrier doping. We consider various scenarios to explain our results, including the possible effects of chemical disorder, electronic inhomogeneity, and a competing phase.Comment: To appear in Phys. Rev.

What Coexists with the Ferromagnetic Metallic Phase in Manganites?

Colossal magnetoresistance, whereby the application of a magnetic field reduces the resistivity of a manganite by orders of magnitude, is generally believed to occur because of coexisting phases. Development of a complete theory to explain the phenomenon requires that the exact nature of these phases be known. We used resonant elastic soft x-ray scattering to examine the superlattice order that exists in La{sub 0.35}Pr{sub 0.275}Ca{sub 0.375}MnO{sub 3} above and below the Curie temperature. By measuring the resonance profile of the scattered x-rays at different values of q, we disentangle the contributions of orbital order and antiferromagnetism to the scattering signal above the Curie temperature. Below the Curie temperature, we see no signal from orbital order, and only antiferromagnetism coexists with the dominant ferromagnetic metallic phase

Environmental baseline monitoring : Phase III final report (2017-2018)

High-quality environmental baseline monitoring data are being collected in areas around two proposed shale gas sites near Kirby Misperton, North Yorkshire and Little Plumpton Lancashire. Monitoring has now been on-going for over two years and has produced an internationally unique data set that will allow any future changes that arise from industrial activities at either or both shale gas sites to be detected and characterised, as well as providing a significant resource for future research. The monitoring includes: water quality, air quality, seismicity, ground motion, soil gas and radon in air. This report presents the results of monitoring in the Vale of Pickering, within which the Kirby Misperton shale gas site (KM8) is located, for the period April 2017–March 2018. It also includes the results of atmospheric composition measurements made near the Little Plumpton (Preston New Road) site. Earlier results and other monitoring in Lancashire are reported elsewhere and can be accessed from the British Geological Survey’s website1. As well as providing valuable insight into the importance of establishing robust information on the conditions before shale gas operations start, it also highlights the challenges in establishing effective monitoring and producing reliable results. For groundwater, this includes the importance of: developing and flushing newly installed boreholes; the spatial variation in water quality and; the selection of monitoring and measuring techniques. Having two years of data has allowed comparison between years. The preliminary analysis reported here has shown that sample populations were not significantly different between the two years. This is directly relevant to the duration of monitoring required by legislation, with the evidence supporting a baseline monitoring period of at least 12 months before any site operations start. The seismic monitoring network installed for measuring background seismicity has operated successfully throughout the reporting period. All but one station show levels of data completeness over 90% which represents a high-quality dataset. There has been no significant change in recorded noise levels at any of the stations in the network. This combined with instrument performance means the network is capable of detecting seismic events with magnitudes of 0.5 ML or less around Kirby Misperton. The monitoring has detected successfully a number of earthquakes around both the Vale of Pickering and the Fylde peninsula. However, all of these are at some distance from the shale gas sites. The Vale of Pickering network has also detected a number of other seismic events that have been attributed to quarry blasts. The magnitudes of these events range from 0.7 ML to 1.6 ML. We have also developed and applied a new magnitude scale to correct for overestimation of magnitudes at small epicentral distances. This results in a significant reduction of the magnitudes of quarry blasts in the Vale of Pickering by over 0.5 magnitude units in some cases. The variance in the magnitude estimates is also slightly reduced. This issue is critical for correct estimation of the magnitudes of any earthquakes that might be induced by hydraulic fracturing. The greenhouse gas monitoring continues to reinforce the conclusion that a baseline at one location is not applicable to other locations. However, the consistency of the baseline measurements (and baseline variability within each year) at both sites clearly suggests that 12 months of baseline monitoring is sufficient to establish a meaningful climatology to compare with analogous climatologies during the operational lifetime of the shale gas sites. Twelve months of data allow differentiation of local and long-range sources of greenhouse gases. At both sites, local (<10 km) sources dominate the contribution to statistically elevated concentration observations. We conclude that: the consistency of the baseline statistics year-to-year at each site separately, strongly validates the utility of these statistics in future comparative work; repeatability and similarity in both mean and statistical variability at each individual site across both annual periods suggests that 12 months of monitoring is sufficient to characterise the baseline at future sites usefully and; the large differences between the baselines at both sites, due to influence of local sources, demonstrate that careful thought and further work may be required to assess the spatial scale over which baselines can be usefully applicable. The baseline distribution of air pollutants measured at the Lancashire site has been broadly similar in 2017 to previous years, but there have been substantial changes observed at Kirby Misperton. There was a noticeable increase in NOx from Autumn 2017 as the site was prepared for hydraulic fracturing operations to begin. The high level of vehicle movements and operation of equipment during this period led to enhanced local NOx emissions. The equipment was removed after operations were suspended and the NOx concentrations returned to broadly the same concentrations seen previously during the baseline period. This highlights the importance of measuring the whole shale-gas operational cycle for air quality as the preparative operations can have a substantial impact on air pollution. In the Vale of Pickering, 133 households volunteered to have detectors for measuring indoor radon concentrations. The results were consistent with the usual log-normal distribution for indoor radon and reflected the locations of the monitoring with respect to whether they were in Radon Affected Areas or not, i.e. radon levels above 200 Bq/m3 were measured in homes in Malton which confirmed the PHE/BGS classification of this location as a Radon Affected Area. Outdoor radon was also measured. There is no indication of elevated outdoor radon concentrations in either the Pickering or Malton Radon Affected Areas, or elsewhere. Results from an active monitor and passive detectors, placed on the Kirby Misperton well site were in good agreement with the average outdoor radon concentrations for the area around Kirby Misperton. The active monitoring showed significant short-term variations over time. However the annual average was consistent, whichever of the techniques was used. Seasonal variability in baseline soil gas and flux values continues to be observed as well as shorter-term diurnal changes and event-driven variations, for example related to the passage of weather systems. The longer-time-series data and the preliminary geostatistical appraisal of selected data suggest that any emissions related to shale gas operations will be easiest to detect in the autumn when baseline biological activity is lower and the soil remains dry. Saturation of the ground in the winter months precludes free gas measurements. A further component of the study is to characterise ground motion (subsidence and/or uplift) in the study areas using satellite data. The objective being to determine what the current situation is, so that any changes that might be caused by hydraulic fracturing, if it takes place, can be identified. The baseline conditions have previously been reported (Ward et al, 2018) and as now hydraulic fracturing has yet taken place, no further analysis has been carried out during this reporting period