Superconductivity in a disordered metal with Coulomb interactions

We study the electronic densities of states (DOS) of strongly disordered superconducting thin films of TiN. We find, using Scanning Tunneling Microscopy (STM) that the DOS decreases towards the Fermi level in the normal phase obtained by applying magnetic fields. The DOS shows spatial fluctuations whose length scale is related to the energy dependent DOS and is similar in normal and superconducting phases. This suggests that Coulomb interactions lead to a spatially varying DOS in the normal phase of a disordered superconductor

The Circumstellar Material around the Type IIP SN 2021yja

International audienceThe majority of Type II-plateau supernovae (SNe IIP) have light curves that are not compatible with the explosions of stars in a vacuum; instead, the light curves require the progenitors to be embedded in circumstellar matter (CSM). We report on the successful fitting of the well-observed SN IIP 2021yja as a core-collapse explosion of a massive star with an initial mass of ∼15 M$_{⊙}$ and a pre-explosion radius of 631 R$_{⊙}$. To explain the early-time behavior of the broadband light curves, the presence of 0.55 M$_{⊙}$ CSM within ∼2 × 10$^{14}$ cm is needed. Like many other SNe IIP, SN 2021yja exhibits an early-time flux excess including ultraviolet wavelengths. This, together with the short rise time (<2 days) in the gri bands, indicates the presence of a compact component in the CSM, essentially adjacent to the progenitor. We discuss the origin of the preexisting CSM, which is most likely a common property of highly convective red supergiant envelopes. We argue that the difficulty in fitting the entire light curve with one spherical distribution indicates that the CSM around the SN 2021yja progenitor was asymmetric

Two-Color VR CCD Photometry of the Intermediate Polar 1RXS J062518.2+733433

Results of 7 nights of CCD VR photometry of the intermediate polar 1RXS J062518.2 +733433 obtained at the Korean 1.8m telescope are reported. The corrected ephemeris for the orbital minimum is BJD (Orb.min) = 2453023.6159 (42)+0.1966431 (33) (E- 1735). The corrected ephemeris for the spin maximum is BJD (spin max) = 2452893 .78477 (10)+0.01374116815 (17) (E-15382) (cycle numbering corresponds to that of Staude et al.~2003). The variations of the shape of the individual spin variations are highly correlated in V and R. The phase of the spin maximum is found to be dependent on the orbital phase. The corresponding semi-amplitude of sinusoidal variations of phase is 0.11±0.03. This new phenomenon is explained by the changing viewing conditions of the accreting magnetic white dwarf, and should be checked in further observations this star and for other intermediate polars. To avoid influence of this effect on the analysis of the long-term spin period variations, the runs of at least one orbital period are recommended. Results of time series analysis are presented in tables

Decomposition Pathways of Titanium Isopropoxide Ti(OⁱPr)₄: New Insights from UV-Photodissociation Experiments and Quantum Chemical Calculations

The UV-photodissociation at 266 nm of a widely used TiO₂ precursor, titanium tetraisopropoxide (Ti­(OⁱPr)₄, TTIP), was studied under molecular-beam conditions. Using the MS-TOF technique, atomic titanium and titanium­(II) oxide (TiO) were detected among the most abundant photofragments. Experimental results were rationalized with the aid of quantum chemical calculations (DLPNO–CCSD­(T) and DFT). Contrary to the existing data in the literature, the new four-centered acetone-elimination reaction was found to be the primary decomposition process of TTIP. According to computational results, the effective activation barrier of this channel was ∼49 kcal/mol, which was ∼13 kcal/mol lower than that of the competing propylene elimination. The former process, followed by the dissociative loss of an H atom, was a dominating channel of TTIP unimolecular decay. The sequential loss of isopropoxy moieties via these two-step processes was supposed to produce the experimentally observed titanium atoms. In turn, the combination of these reactions with propylene elimination can lead to another detected species, TiO. These results indicate that the existing mechanisms of TTIP thermal and photoinitiated decomposition in the chemical-vapor deposition (CVD) of titanium dioxide should be reconsidered

Quantum Yield and Mechanism of Singlet Oxygen Generation via UV Photoexcitation of O₂–O₂ and N₂–O₂ Encounter Complexes

The mechanism and spectral dependence of the quantum yield of singlet oxygen O₂(a ¹Δ_g) photogenerated by UV radiation in gaseous oxygen at elevated pressure (32–130 bar) have been experimentally investigated within the 238–285 nm spectral region overlapping the range of the Wulf bands in the absorption spectrum of oxygen. The dominant channel of singlet oxygen generation with measured quantum yield up to about 2 is attributed to the one-quantum absorption by the encounter complexes O₂–O₂. This absorption gives rise to oxygen in the Herzberg III state O₂(A′ ³Δ_u), which is assumed to be responsible for singlet oxygen production in the relaxation process O₂(A′ ³Δ_u, υ) + O₂(X ³Σ_g^–) → O₂({a ¹Δ_g}, {b ¹Σ_g⁺}) + O₂({a ¹Δ_g, υ = 0}, {b ¹Σ_g⁺, υ = 0}) with further collisional relaxation of b to a state. This mechanism is deduced from the analysis of the avoiding crossing locations on the potential energy surface of colliding O₂–O₂ pair. The observed drop of the O₂(a ¹Δ_g) yield near spectral threshold for O₂ dissociation is explained by the competition between above relaxation and reaction giving rise to O₃ + O (O + O + O₂) supposed in literature. The quantum yield of O₂(a ¹Δ_g) formation from encounter complex N₂–O₂ measured at λ = 266 nm was found to be the same as that for O₂–O₂