Pressure cycle of superconducting Cs0.8Fe2Se2 : A transport study

We report measurements of the temperature and pressure dependence of the electrical resistivity (ρ) of single-crystalline iron-based chalcogenide Cs_0.8Fe₂Se₂. In this material, superconductivity with a transition temperature develops from a normal state with extremely large resistivity. At ambient pressure, a large “hump” in the resistivity is observed around 200 K. Under pressure, the resistivity decreases by two orders of magnitude, concomitant with a sudden T_c suppression around . Even at 9 GPa a metallic resistivity state is not recovered, and the ρ(T) “hump” is still detected. A comparison of the data measured upon increasing and decreasing the external pressure leads us to suggest that the superconductivity is not related to this hump.     

Diode laser spectroscopy of CO2 at 790 nm

Absorption lines of ¹²C¹⁶O₂ have been examined by using a tunable diode laser spectrometer in the region around (790 nm). The spectrometer sources are commercially available double heterostructure InGaAlAs tunable diode lasers (TDLs) operating in the “free-running” mode, which allowed the detection of the line positions within . The observed carbon dioxide absorption lines belong to the combination overtone 2ν₂+5ν₃ ro-vibrational band with intensities ranging around .     

MRCI studies on the electronic structure of AlN and AlN, and the electron affinity of AlN

Using multireference configuration-interaction methods and double to triple-zeta basis sets with semidiffuse and polarization functions, potential energies and spectroscopic constants for low-lying doublet, and quartet states of AlN⁻ were calculated. has R_e=3.280 bohr and . lies 0.17 eV above the ground state. Using an estimated electron affinity of 2.1 eV for AlN, four states of AlN⁻ are found to be stable, namely , , , and . Comparisons with the isovalent anions BN⁻ (three stable states) and AlP⁻ (seven stable states) are made. Photo-detachment of an electron from the state of AlN⁻ can lead to an accurate determination of the energy difference between the two close-lying lowest states of AlN, and , predicted here to be 0.09 eV apart.     

On the large N limit of conformal field theory

Following recent advances in large N matrix mechanics, I discuss here the free (Cuntz) algebraic formulation of the large N limit of two-dimensional conformal field theories of chiral adjoint fermions and bosons. One of the central results is a new affine free algebra which describes a large N limit of affine Lie algebra. Other results include the associated free-algebraic partition functions and characters, a free-algebraic coset construction, free-algebraic construction of , free-algebraic vertex operator constructions in the large N Bose systems, and a provocative new free-algebraic factorization of the ordinary Koba-Nielsen factor.     

Diode laser overtone spectroscopy of CO2 at 780 nm

Overtone absorption lines of ¹²C¹⁶O₂ have been examined by using a tunable diode laser (TDL) spectrometer in the region around . The spectrometer sources are commercially available double heterostructure InGaAlAs TDLs operating in the “free-running” mode, which allowed the detection of the line positions within . The observed carbon dioxide absorption lines belong to the ν₁+5ν₃ ro-vibrational band with rotational quantum number J up to 48. The minimum absorbance detected by the spectrometer (?5×10^-6) permitted to observe the weakest lines having the absorption cross section of the order of .     

Microwave study of the rotational spectrum of oxygen molecule in the range up to 1.12 THz

Microwave study of the rotational transitions of oxygen molecule in its electronic and vibrational ground states is reported. Eight transitions belonging to N=3-1, N=5-3, and N=7-5 groups were investigated. Central line frequencies and pressure broadening parameters for O₂ and N₂ as perturbers were determined. The highest frequency of measured transition (N,J)=(7,6)-(5,6) has been 1.12 THz. Spectrometer with backward wave oscillator (BWO) and acoustic detector (RAD) was used. Since this experiment has more than doubled the number of previously measured rotational lines of oxygen molecule and better accuracy was achieved, the fitting of new set of rotational transition frequencies has been performed and new more accurate molecular constants for in , v=0 state have been obtained.     

The quark model and b baryons

The recent observation at the Tevatron of (uub and ddb) baryons within 2 MeV of the predicted Σ_b-Λ_b splitting and of baryons at the Tevatron within a few mega electron volts (MeV) of predictions has provided strong confirmation for a theoretical approach based on modeling the color hyperfine interaction. The prediction of  = 5790-5800 MeV is reviewed and similar methods used to predict the masses of the excited states and . The main source of uncertainty is the method used to estimate the mass difference m_b-m_c from known hadrons. We verify that corrections due to the details of the interquark potential and to Ξ_b- mixing are small. For S-wave qqb states we predict , and . For states with one unit of orbital angular momentum between the b quark and the two light quarks we predict , and . Results are compared with those of other recent approaches.