Anisotropic Thermal Expansion of p-Terphenyl: a Self-Assembled Supramolecular Array of Poly-p-phenyl Nanoribbons

Abstract

The recent discovery of superconductivity in a metallic aromatic hydrocarbon, alkali-doped p-Terphenyl, has attracted considerable interest. The critical temperature T c ranges from few to 123 K, the record for organic superconductors, due to uncontrolled competition of multiple phases and dopants concentrations. In the proposed mechanism of Fano resonance in a superlattice of quantum wires with coexisting polarons and Fermi particles, the lattice properties play a key role. Here we report a study of the temperature evolution of the parent compound p-Terphenyl crystal structure proposed to be made of a self-assembled supramolecular network of nanoscale nanoribbons. Using temperature dependent synchrotron radiation x-ray diffraction we report the anisotropic thermal expansion in the ab plane, which supports the presence of a nanoscale network of one-dimensional nanoribbons running in the b-axis direction in the P21/a structure. Below the enantiotropic phase transition at 193 K the order parameter of the C-1 structure follows a power law behaviour with the critical exponent α = 0.34±0.02 and the thermal expansion of the a-axis and b-axis show major changes supporting the formation of a two-dimensional bonds network. The large temperature range of the orientation fluctuations in a double well potential of the central phenyl has been determined.

Vibrational Properties of p-Terphenyl

“…According to previous theoretical works, , the planarity plays an important role in the vibrational properties. The p -terphenyl molecules exhibit strong thermal librations around the c axes in the disorder state, and they suddenly quiet down after the “order–disorder” type transition. ,− In our work, the intensity ratio of the 1280 cm –1 mode and the 1220 cm –1 mode, as well as the intensity ratio of the two modes at around 1600 cm –1 , remains constant down to the transition temperature. This indicates that the amplitude of the interring librations does not change until 193 K. Upon cooling, almost all the modes rapidly decrease their fwhms.…”

Potassium-Doped Para-Terphenyl: Structure, Electrical Transport Properties and Possible Signatures of a Superconducting Transition

“…The room temperature (RT) structure was described as a packing of nanoribbons, made of p-terphenyl molecules, in the crystallographic b direction. Therefore, the structure of the molecule can be interpreted as a realization of a nanoscale architecture of low dimensional systems 11,12 described as a self-organized array of polymeric quantum stripes 13,14 . While pristine p-terphenyl is electrically insulating, it behaves as a metal upon K-doping 15 .…”

Evolution of Complexity in Out-of-Equilibrium Systems by Time-Resolved or Space-Resolved Synchrotron Radiation Techniques

“…Moreover, they allow us to prevent radiation damage on biological samples providing new key information [70][71][72]. In this work, we present some relevant results showing the relationship between new geometries developing at nano/mesoscale and the emerging macroscopic properties in complex and heterogeneous systems in different fields opening new fundaments in natural sciences [73][74][75][76][77][78][79][80][81][82][83][84].…”