Superconducting properties of (NH₃)_yLi_xFeSe_0.5Te_0.5 under pressure

Abstract

We prepared two superconducting phases of (NH 3 ) y Li x FeSe 0.5 Te 0.5 , which show superconducting transition temperatures (T c 's) as high as 20.2 and 29.5 K at ambient pressure, here called the 'low-T c phase' and 'high-T c phase'. The temperature dependence of electrical resistance (R) was measured for the low-T c phase of (NH 3 ) y Li x FeSe 0.5 Te 0.5 over a pressure (p) range of 0-14 GPa, and for the high-T c phase of (NH 3 ) y Li x FeSe 0.5 Te 0.5 over 0-19 GPa, yielding double-dome superconducting T c -p phase diagrams, i.e. two superconducting phases (SC-I and SC-II) were found for both the low-T c and high-T c phases under pressure. For the low-T c phase, the maximum T c was 20.2 K at 0 GPa for SC-I, and 19.9 K at 8.98 GPa for SC-II. For the high-T c phase, the maximum T c was 33.0 K at 1.00 GPa for SC-I, and 24.0 K at 11.5-13.2 GPa for SC-II. These results imply that the maximum T c value of the high pressure phase (SC-II) does not exceed the maximum value of the SC-I, unlike what was shown in the T c -p phase diagrams of (NH 3 ) y Li x FeSe and (NH 3 ) y Cs x FeSe investigated previously. Nevertheless, the double-dome T c -p phase diagram was found in metal-doped FeSe 0.5 Te 0.5 , indicating that this feature is universal in metal-doped FeSe 1−z Te z . Moreover, no structural phase transitions were observed for either the low-T c or high-T c phases of (NH 3 ) y Li x FeSe 0.5 Te 0.5 over the wide pressure range of 0-15.3 GPa, and the T c -lattice constant (c) plots for both phases were recorded to determine the critical point separating SC-I and SC-II.

A New Technique for Measuring Polycyclic Aromatic Hydrocarbon Emission in Different Environments

“…For example, the PAH bands of laboratory-measured spectra, which are commonly detected in absorption, are too narrow to be compatible with astronomical spectra, which are commonly seen in emission. On the other hand, the quantum-chemically computed spectra suffer from the fact that the band positions and strength are often not accurate and need to be scaled (Yang et al 2017a(Yang et al , 2017b. Finally, the laboratory measurements are so far limited to PAHs smaller than ∼ 50 C atoms (Hudgins & Allamandola 2005), while interstellar PAHs can be much larger (see Figure 7 of Draine & Li 2007).…”