Electron pockets and pseudogap asymmetry observed in the thermopower of underdoped cuprates

We calculate the diffusion thermoelectric power of high-Tc cuprates using the resonating-valence-bond spin-liquid model developed by Yang, Rice and Zhang (YRZ). In this model, reconstruction of the energy-momentum dispersion results in a pseudogap in the density of states that is heavily asymmetric about the Fermi level. The subsequent asymmetry in the spectral conductivity is found to account for the large magnitude and temperature dependence of the thermopower observed in underdoped cuprates. In addition we find evidence in experimental data for electron pockets in the Fermi surface, arising from a YRZ-like reconstruction, near the onset of the pseudogap in the slightly overdoped regime.Comment: 6 pages, 7 figures, accepted for publication in EP

Observations of far-infrared fine structure lines: o III88.35 micrometer and oI 63.2 micrometer

Observations of the O III 88.35 micrometer line and the O I63.2 micrometer were made with a far infrared spectrometer. The sources M17, NGC 7538, and W51 were mapped in the O III line with 1 arc minute resolution and the emission is found to be quite widespread. In all cases the peak of the emission coincides with the maximum radio continuum. The far infrared continuum was mapped simultaneously and in M17, NGC 7538, and W51 the continuum peak is found to be distinct from the center of ionization. The O III line was also detected in W3, W49, and in a number of positions in the Orion nebula. Upper limits were obtained on NGS 7027, NGC 6572, DR21, G29.9-0.0 and M82. The 63.2 micrometer O I line was detected in M17, M42, and marginally in DR21. A partial map of M42 in this line shows that most of the emission observed arises from the Trapezium and from the bright optical bar to the southeast

Detection of interstellar NH sub 3 in the far-warm and dense gas in Orion-KL

The detection of the (J,K) = a(4,3) yields s(3,3) rotation inversion transition of ammonia at 124.6 microns toward the center of the Orion-KL region is reported. The line is in emission and has a FWHM or = to 30 km s 0.15. The far IR ammonia line emission probably comes mainly from the 'hot core', a compact region of warm, very dense gas previously identified by the radio inversion lines of NH3. The a(4,3) yields s(3,3) line is very optically thick, and since it is seen in emission, radiative excitation of the (4,3) NH3 level by far IR emission from dust within the source can be ruled out. Radiative excitation via the 10 microns of vibrational transitions of NH3 also seems unlikely. Hence, the (4,3) level is probably collisionally excited and the gas in the hot core region is warmer than the dust. Since the far IR line emission is highly trapped, densities of approximately 10 to the 7th power cu cm are high enough to explain the observations. Shock heating by the mass outflow from IRc2 may account for the high gas temperatures in the hot core region

Saddle-point van Hove singularity and the phase diagram of high-Tc cuprates

We examine the generic phase behavior of high-Tc cuprate superconductors in terms a universal van Hove singularity in the strongly overdoped region. Using a rigid ARPES-derived dispersion we solve the BCS gap equation and show that the pairing interaction or pairing energy cutoff must be a rapidly declining function of doping. This result is prejudicial to a phonon-based pairing interaction and more consistent with a magnetic or magnetically enhanced interaction.Comment: 5 pages, 2 figures, submitted to Physical Review

Far-infrared rotational emission by carbon monoxide

Accurate theoretical collisional excitation rates are used to determine the emissivities of CO rotational lines 10 to the 4th power/cu cm n(H2), 100 K T 2000 K, and J 50. An approximate analytic expression for the emissitivities which is valid over most of this region is obtained. Population inversions in the lower rotational levels occur for densities n(H2) approximately 10 (to the 3rd to 5th power)/cu cm and temperatures T approximately 50 K. Interstellar shocks observed edge on are a potential source of millimeter wave CO maser emission. The CO rotational cooling function suggested by Hollenbach and McKee (1979) is verified, and accurate numerical values given. Application of these results to other linear molecules should be straightforward

Overcoming the boundary layer turbulence at Dome C: ground-layer adaptive optics versus tower

The unique atmospheric conditions present at sites such as Dome C on the Antarctic plateau are very favorable for high spatial resolution astronomy. At Dome C, the majority of the optical turbulence is confined to a 30 to 40 m thick stable boundary layer that results from the strong temperature inversion created by the heat exchange between the air and the ice-covered ground. To fully realize the potential of the exceptionally calm free atmosphere, this boundary layer must be overcome. In this article we compare the performance of two methods proposed to beat the boundary layer: mounting a telescope on a tower that physically puts it above the turbulent layer, and installing a telescope at ground level with a ground-layer adaptive optics system. A case is also made to combine these two methods to further improve the image quality

Thermodynamic properties of Bi2Sr2CaCu2O8 calculated from the electronic dispersion

The electronic dispersion for Bi2Sr2CaCu2O(8+d) has been determined from angle-resolved photoelectron spectroscopy (ARPES). From this dispersion we calculate the entropy and superfluid density. Even with no adjustable parameters we obtain an exceptional match with experimental data across the entire phase diagram, thus indirectly confirming both the ARPES and thermodynamic data. The van Hove singularity is crossed in the overdoped region giving a distinctive linear-in-T temperature dependence in the superfluid density there.Comment: 5 pages, 4 figures, submitted to Physical Review Letter

Double layer in ionic liquids: Overscreening vs. crowding

We develop a simple Landau-Ginzburg-type continuum theory of solvent-free ionic liquids and use it to predict the structure of the electrical double layer. The model captures overscreening from short-range correlations, dominant at small voltages, and steric constraints of finite ion sizes, which prevail at large voltages. Increasing the voltage gradually suppresses overscreening in favor of the crowding of counterions in a condensed inner layer near the electrode. The predicted ion profiles and capacitance-voltage relations are consistent with recent computer simulations and experiments on room-temperature ionic liquids, using a correlation length of order the ion size.Comment: 4 pages + supplementary informatio