Ren-Shu Wang

Structural and Bonding Characteristics of Potassium-Doped p-Terphenyl Superconductors

Recently, there is a series of reports by Wang et al. on the superconductivity in K-doped p-terphenyl (KxC18H14) with the transition temperatures ranging from 7 to 123 K. Identifying the structural and bonding characteristics is the key to understand the superconducting phases and the related properties. Therefore, we carried out an extensive study on the crystal structures with different doping levels and investigated the thermodynamic stability, structural, electronic, and magnetic properties by the first-principles calculations. Our calculated structures capture most features of the experimentally observed X-ray diffraction patterns. The K-doping concentration is constrained to within the range of 2–3. The obtained formation energy indicates that the system at x = 2.5 is more stable. The strong ionic bonding interaction is found in between K atoms and organic molecules. The charge transfer accounts for the metallic feature of the doped materials. For a small amount of charge transferred, the tilting fo...

Vibrational Properties of p-Terphenyl

Vibrational properties associated with the intra- and intermolecular terms of pristine p-terphenyl at low temperatures are analyzed in detail by Raman spectroscopy. Nearly all of the vibrational modes exhibit anomalous behaviors at the transition temperature of about 193 K on the frequencies, widths, and intensities. Meanwhile, the drastic drops of the spectrum weight result in the splits of many peaks like the lattice vibrational peaks and the peaks located at around 1220, 1280, and 1600 cm-1. All the anomalies result from the drastic decrease of the vibrational anharmonic coupling effects in the crystalline p-terphenyl after entering into the ordered state. The rapidly declining anharmonicity also makes contributions to the anomalous behaviors of the intensity ratios of the 1220, 1280, and 1600 cm-1 modes, as well as the energy separations between the combination bands and the fundamental bands. Our work is of great significance to understand the internal vibrational properties of p-terphenyl.

Superconductivity at 3.5 K and/or 7.2 K in potassium-doped triphenylbismuth

We develop a two-step synthesis method-ultrasound treatment and low temperature annealing to explore superconductivity in potassium-doped triphenylbismuth, which is composed of one bismuth atom and three phenyl rings. The combination of dc and ac magnetic measurements reveals that one hundred percent of synthesized samples exhibit superconductivity at 3.5 K and/or 7.2 K at ambient pressure. The magnetization hysteresis loops provide a strong piece of evidence of type-II superconductors. It is found that the doped materials crystallize into the triclinic P1 structure, with a mole ratio of 4:1 between potassium and triphenylbismuth. Both the calculated electronic structure and measured Raman spectra indicate that superconductivity is realized by transferring electrons from the K-4s to C-2p orbital. Our study opens an encouraging window for the search of organic superconductors in organometallic molecules.