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

BiOCuS: A new superconducting compound with oxypnictide - related structure

The discovery of about 50 K superconductivity in the tetragonal Fe-based pnictides has stimulated the search for superconductivity in a wide class of materials with similar structure. Copper forms compounds isostructural to LaOFeAs. Single phase BiOCuS can be prepared by a solid state reaction at temperature lower than 500 C from a mixture of Bi2O3, Bi2S3 and Cu2S. The samples have been characterized by means of EDX analysis, X-ray diffraction, magnetic and electrical measurements. The cell parameters are a = 3.8708 A, c = 8.565 A. Charge carrier doping can be realized either by F substitutions for O, or by Cu off-stoichiometry. The latter doping route leads to the occurrence of superconductivity below Tc = 5.8 K

Induction methods used in low temperature physics

A study has been made of induction bridges used in low temperature physics.\ud \ud In Part 1 the design of a mutual inductance bridge of the Hartshorn type is discussed. This design is based on a critical analysis of impurity effects of the different parts of the Hartshorn bridge. With this equipment frequencies up to 0.5 MHz can be used. Two methods have been developed to examine the secondary signal. In one of these use has been made of AD conversion techniques. In the other one, the secondary signal, produced by a superconducting sample, which is generally distorted, is analysed by using a Fourier expansion.\ud \ud In Part 2 equipment is described which enables us to measure the phase and amplitude of the harmonics of the output signal of the bridge. For synchronous detection a reference signal of the same frequency of the harmonic of interest is required. This reference signal is generated from the input signal of the bridge by means of a digital frequency multiplier with programmable multiplication factor N.\ud \ud In Part 3 some experimental results, showing the possibilities of the equipment, on some superconductors are presented

The black hole in IC 1459 from HST observations of the ionized gas disk

The peculiar elliptical galaxy IC 1459 (M_V = -21.19, D = 16.5 Mpc) has a fast counterrotating stellar core, stellar shells and ripples, a blue nuclear point source and strong radio core emission. We present results of a detailed HST study of IC 1459, and in particular its central gas disk, aimed a constraining the central mass distribution. We obtained WFPC2 narrow-band imaging centered on the Halpha+[NII] emission lines to determine the flux distribution of the gas emission at small radii, and we obtained FOS spectra at six aperture positions along the major axis to sample the gas kinematics. We construct different dynamical models for the Halpha+[NII] and Hbeta kinematics that include a supermassive black hole, and in which the stellar mass distribution is constrained by the observed surface brightness distribution and ground-based stellar kinematics. All models are consistent with a black hole mass in the range Mbh=1-4 x 10^8 Msun, and models without a black hole are always ruled out at high confidence.Comment: 40 pages including 14 figures, Latex; submitted to A

Black Hole Masses and Host Galaxy Evolution of Radio-loud Active Galactic Nuclei

We report stellar velocity dispersion measurements for a sample of 28 AGN host galaxies including our previous work. Using the mass-dispersion ($M_{\bullet}-\sigma$) and the fundamental plane relations, we estimate the black hole mass for a sample of 66 BL Lac objects and investigate the role of black hole mass in the energetics of BL Lac objects. The black hole mass range for different BL Lac spectral types is similar, $10^{7} < M_{\bullet} < 4 \times 10^{9}$. Neither X-ray nor radio luminosity correlates with black hole mass. Low-frequency-peaked BL Lac objects have higher Eddington ratios on average, because of either more beaming or higher intrinsic power. For the black hole mass range $3 \times 10^{7} < M_{\bullet} < 10^{9}$, the radio luminosity of BL Lac objects and flat-spectrum radio quasars spans over 4 orders of magnitude, with BL Lac objects being low-power AGNs. We also investigate the evolution of host galaxies for 39 AGNs out to $z \approx 0.5$ with measuredstellar velocity dispersions. Comparing the mass-to-light ratio evolution in the observed frame with population synthesis models, we find that single burst star formation models with $z_{form} = 1.4^{+0.9}_{-0.2}$ are consistent with the observations. From our $z_{form}=1.4$ model, we estimated the intrinsic mass-to-light ratio evolution in the Cousins $R$ band, $\Delta log (M/L)/ \Delta z = -0.502 \pm 0.08$, consistent with that of normal early type galaxies.Comment: ApJ accepted, 22 pages, 11 figure

An Accreting Black Hole in the Nuclear Star Cluster of the Bulgeless Galaxy NGC 1042

We present spectroscopic evidence for a low-luminosity, low-excitation active galactic nucleus (AGN) in NGC 1042, powered by an intermediate-mass black hole. These findings are significant in that the AGN is coincident with a compact star cluster known to reside in the nucleus, thus providing an example where the two types of central mass concentration coexist. The existence of a central black hole is additionally remarkable in that NGC 1042 lacks a stellar bulge. Objects such as NGC 1042 may have an important role in testing theories for the genesis of massive black holes in galaxy nuclei, and the extent to which they are in symbiosis with the larger stellar host.Comment: 15 pages, 6 figures, accepted for publication in Ap